Providing a computationally derived, mechanically optimised target correction during preoperative planning can improve joint contact mechanics of hip dysplasia treated with periacetabular osteotomy

AIM

Preoperative identification of acetabular corrections that optimally improve joint stability and reduce elevated contact stresses could further reduce osteoarthritis progression in patients with hip dysplasia who are treated with periacetabular osteotomy (PAO). The purpose of this study was to investigate how providing patient-specific, mechanically optimal acetabular reorientations to the surgeon during preoperative planning affected the surgically achieved correction.

METHODS

Preoperative CT scans were used to create patient-specific hip models for 6 patients scheduled for PAO. A simulated acetabular fragment was extracted from the preoperative pelvis model and computationally rotated to simulate candidate acetabular reorientations. For each candidate, discrete element analysis was used to compute contact stresses during walking, which were summed over the gait cycle and scaled by patient age to obtain chronic contact stress-time exposure. The ideal patient-specific reorientation was identified using a cost function that balances minimising chronic stress exposures and achieving surgically acceptable acetabular coverage angles. The optimal reorientation angles and associated contact mechanics were provided to the surgeon preoperatively. After PAO was performed, a model of the surgically achieved correction was created from a postoperative CT scan. Radiographic coverage and contact mechanics were compared between preoperative, optimal, and surgically achieved orientations.

RESULTS

While surgically achieved reorientations were not significantly different from optimal reorientations in radiographically measured lateral (p = 0.094) or anterior (p = 0.063) coverage, surgically achieved reorientations had significantly (p = 0.031) reduced total contact area compared to optimal reorientations. The difference in lateral coverage and peak chronic exposure between surgically achieved and optimal reorientations decreased with increasing surgeon experience using the models (R² = 0.758, R2 = 0.630, respectively).

CONCLUSIONS

Providing hip surgeons with a patient-specific, computationally optimal reorientation during preoperative planning may improve contact mechanics after PAO, which may help reduce osteoarthritis progression in patients with hip dysplasia.

Does Patient-specific Functional Pelvic Tilt Affect Joint Contact Pressure in Hip Dysplasia? A Finite-element Analysis Study

BACKGROUND

Although individual and postural variations in the physiologic pelvic tilt affect the acetabular orientation and coverage in patients with hip dysplasia, their effect on the mechanical environment in the hip has not been fully understood. Individual-specific, finite-element analyses that account for physiologic pelvic tilt may provide valuable insight into the contact mechanics of dysplastic hips, which can lead to further understanding of the pathogenesis and improved treatment of this patient population.

QUESTION/PURPOSE

We used finite-element analysis to ask whether there are differences between patients with hip dysplasia and patients without dysplasia in terms of (1) physiologic pelvic tilt, (2) the pelvic position and joint contact pressure, and (3) the morphologic factors associated with joint contact pressure.

METHODS

Between 2016 and 2019, 82 patients underwent pelvic osteotomy to treat hip dysplasia. Seventy patients with hip dysplasia (lateral center-edge angle ≥ 0° and < 20° on supine AP pelvic radiographs) were included. Patients with advanced osteoarthritis, femoral head deformity, prior hip or supine surgery, or poor-quality imaging were excluded. Thirty-two patients (32 hips) were eligible to this finite-element analysis study. For control groups, we reviewed 33 female volunteers without a history of hip disease. Individuals with frank or borderline hip dysplasia (lateral center-edge angle < 25°) or poor-quality imaging were excluded. Sixteen individuals (16 hips) were eligible as controls. Two board-certified orthopaedic surgeons measured sagittal pelvic tilt (the angle between the anterior pelvic plane and vertical axis: anterior pelvic plane [APP] angle) and acetabular version and coverage using pelvic radiographs and CT images. Intra- and interobserver reliabilities, evaluated using the kappa value and intraclass correlation coefficient, were good or excellent. We developed individual-specific, finite-element models using pelvic CT images, and performed nonlinear contact analysis to calculate the joint contact pressure on the acetabular cartilage during the single-leg stance with respect to three pelvic positions: standardized (anterior pelvic plane), supine, and standing. We compared physiologic pelvic tilt between patients with and without dysplasia using a t-test or the Wilcoxon rank sum test. A paired t-test or the Wilcoxon signed rank test with a Bonferroni correction was used to compare joint contact pressure between the three pelvic positions. We correlated joint contact pressure with morphologic parameters and pelvic tilt using the Pearson or the Spearman correlation coefficients.

RESULTS

The APP angle in the supine and standing positions varied widely among individuals. It was greater in patients with hip dysplasia than in patients in the control group when in the standing position (3° ± 6° versus -2° ± 8°; mean difference 5° [95% CI 1° to 9°]; p = 0.02) but did not differ between the two groups when supine (8° ± 5° versus 5° ± 7°; mean difference 3° [95% CI 0° to 7°]; p = 0.06). The mean pelvic tilt was 6° ± 5° posteriorly when shifting from the supine to the standing position in patients with hip dysplasia. The median (range) maximum contact pressure was higher in dysplastic hips than in control individuals (in standing position; 7.3 megapascals [MPa] [4.1 to 14] versus 3.5 MPa [2.2 to 4.4]; difference of medians 3.8 MPa; p < 0.001). The median maximum contact pressure in the standing pelvic position was greater than that in the supine position in patients with hip dysplasia (7.3 MPa [4.1to 14] versus 5.8 MPa [3.5 to 12]; difference of medians 1.5 MPa; p < 0.001). Although the median maximum joint contact pressure in the standardized pelvic position did not differ from that in the standing position (7.4 MPa [4.3 to 15] versus 7.3 MPa [4.1 to 14]; difference of medians -0.1 MPa; p > 0.99), the difference in the maximum contact pressure varied from -3.3 MPa to 2.9 MPa, reflecting the wide range of APP angles (mean 3° ± 6° [-11° to 14°]) when standing. The maximum joint contact pressure in the standing position was negatively correlated with the standing APP angle (r = -0.46; p = 0.008) in patients with hip dysplasia.

CONCLUSION

Based on our findings that individual and postural variations in the physiologic pelvic tilt affect joint contact pressure in the hip, future studies on the pathogenesis of hip dysplasia and joint preservation surgery should not only include the supine or standard pelvic position, but also they need to incorporate the effect of the patient-specific pelvic tilt in the standing position on the biomechanical environment of the hip.

CLINICAL RELEVANCE

We recommend assessing postural change in sagittal pelvic tilt when diagnosing hip dysplasia and planning preservation hip surgery because assessment in a supine or standard pelvic position may overlook alterations in the hip's contact mechanics in the weightbearing positions. Further studies are needed to elucidate the effect of patient-specific functional pelvic tilt on the degeneration process of dysplastic hips, the acetabular reorientation maneuver, and the clinical result of joint preservation surgery.

Does Cup Position at the High Hip Center or Anatomic Hip Center in THA for Developmental Dysplasia of the Hip Result in Better Harris Hip Scores and Revision Incidence? A Systematic Review

BACKGROUND

One goal of THA is to restore the anatomic hip center, which can be achieved in hips with developmental dysplasia by placing cups at the level of the native acetabulum. However, this might require adjuvant procedures such as femoral shortening osteotomy. Another option is to place the cup at the high hip center, potentially reducing surgical complexity. Currently, no clear consensus exists regarding which of these cup positions might offer better functional outcomes or long-term survival.

QUESTION/PURPOSE

We performed a systematic review to determine whether (1) functional outcomes as measured by the Harris hip score, (2) revision incidence, and (3) complications that do not result in revision differ based on the position of the acetabular cup (high hip center versus anatomic hip center) in patients undergoing THA for developmental dysplasia of the hip (DDH).

METHODS

We performed a systematic review using Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines, including studies comparing the functional outcomes, revision incidence, and complications of primary THA in dysplastic hips with acetabular cups placed at the high hip center versus those placed at the anatomic hip center, over any time frame. The review protocol was registered with PROSPERO (registration number CRD42020168183) before commencement. Of 238 records, eight comparative, retrospective nonrandomized studies of interventions were eligible for our systematic review, reporting on 207 hips with cups placed at the high hip center and 268 hips with cups at the anatomic hip center. Risk of bias within eligible studies was assessed using the Risk Of Bias In Non-randomized Studies of Interventions tool. Due to low comparability between studies, data could not be pooled, so these studies were assessed without summary effects.

RESULTS

Six studies compared Harris hip scores, two of which favored high hip center cup placement and three of which favored anatomic hip center cup placement, although none of the differences between cohorts met the minimum clinically important difference. Five studies reliably compared revision incidence, which ranged from 2% to 9% for high hip center at 7 to 15 years and 0% to 5.9% for anatomic hip center at 6 to 16 years. Five studies reported intra- and postoperative complications, with the high hip center being associated with higher incidence of dislocation and lower incidence of neurological complications. No clear difference was observed in intraoperative complications between the high hip center and anatomic hip center.

CONCLUSION

No obvious differences could be observed in Harris hip score or revision incidence after THA for osteoarthritis secondary to DDH between cups placed at the anatomic hip center and those placed at the high hip center. Placement of the acetabular cup in the high hip center may lead to higher risk of dislocation but lower risk of neurologic complications, although no difference in intraoperative complications was observed. Surgeons should be able to achieve satisfactory functional scores and revision incidence using either technique, although they should be aware of how their choice influences hip biomechanics and the need for adjunct procedures and associated risks and operative time. These recommendations should be considered with respect to the several limitations in the studies reviewed, including the presence of serious confounding factors and selection biases, inconsistent definitions of the high hip center, variations in dysplasia severity, small sample sizes, and follow-up periods. These weaknesses should be addressed in well-designed future studies.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Does the Rule of Thirds Adequately Detect Deficient and Excessive Acetabular Coverage?

BACKGROUND

Assessment of AP acetabular coverage is crucial for choosing the right surgery indication and for obtaining a good outcome after hip-preserving surgery. The quantification of anterior and posterior coverage is challenging and requires either other conventional projections, CT, MRI, or special measurement software, which is cumbersome, not widely available and implies additional radiation. We introduce the "rule of thirds" as a promising alternative to provide a more applicable and easy method to detect an excessive or deficient AP coverage. This method attributes the intersection point of the anterior (posterior) wall to thirds of the femoral head radius (diameter), the medial third suggesting deficient and the lateral third excessive coverage.

QUESTION/PURPOSE

What is the validity (area under the curve [AUC], sensitivity, specificity, positive/negative likelihood ratios [LR(+)/LR(-)], positive/negative predictive values [PPV, NPV]) for the rule of thirds to detect (1) excessive and (2) deficient anterior and posterior coverages compared with previously established radiographic values of under-/overcoverage using Hip2Norm as the gold standard?

METHODS

We retrospectively evaluated all consecutive patients between 2003 and 2015 from our institutional database who were referred to our hospital for hip pain and were potentially eligible for joint-preserving hip surgery. We divided the study group into six specific subgroups based on the respective acetabular pathomorphology to cover the entire range of anterior and posterior femoral coverage (dysplasia, overcoverage, severe overcoverage, excessive acetabular anteversion, acetabular retroversion, total acetabular retroversion). From this patient cohort, 161 hips were randomly selected for analysis. Anterior and posterior coverage was determined with Hip2Norm, a validated computer software program for evaluating acetabular morphology. The anterior and posterior wall indices were measured on standardized AP pelvis radiographs, and the rule of thirds was applied by one observer.

RESULTS

The detection of excessive anterior and posterior acetabular wall using the rule of thirds revealed an AUC of 0.945 and 0.933, respectively. Also the detection of a deficient anterior and posterior acetabular wall by applying the rule of thirds revealed an AUC of 0.962 and 0.876, respectively. For both excessive and deficient anterior and posterior acetabular coverage, we found high specificities and PPVs but low sensitivities and NPVs.

CONCLUSION

We found a high probability for an excessive (deficient) acetabular wall when this intersection point lies in the lateral (medial) third, which would qualify for surgical correction. On the other hand, if this point is not in the lateral (medial) third, an excessive (deficient) acetabular wall cannot be categorically excluded. Thus, the rule of thirds is very specific but not as sensitive as we had expected.

LEVEL OF EVIDENCE

Level II, diagnostic study.

High Risk of Conversion to THA After Femoroacetabular Osteoplasty for Femoroacetabular Impingement in Patients Older than 40 Years

BACKGROUND

Femoroacetabular impingement (FAI) is a recognized cause of hip pain and decreased quality of life and has been linked to primary idiopathic hip osteoarthritis (OA). Although the operative indications for FAI have expanded to include older patients, we do not know whether there is an increased risk of conversion to THA after femoroacetabular osteoplasty (FAO) via the mini-open approach for FAI in patients older than 40 years compared with younger patients, after controlling for other confounding variables.

QUESTIONS/PURPOSES

(1) After matching for gender, BMI, preoperative symptomatic period, surgeon experience, Tönnis grade, and degree of chondral lesion, are patients older than 40 years who undergo FAO for FAI more likely to be revised to THA at a minimum of 2 years' follow-up than are patients younger than 40? (2) Is there a difference in delta (postoperative minus preoperative) improvement in functional outcome scores in those patients who did not go on to THA between patients older than and younger than 40 years?

METHODS

Between 2003 and 2017, one surgeon performed 281 FAOs via the mini-open approach in patients older than 40 years and 544 of the same procedure in patients younger than 40 years. During that period, the general indications for FAO were the same in both age groups: (1) history and physical exam consistent with FAI, (2) radiographic evidence of focal impingement (cam, pincer, or both), (3) evidence of labral or chondrolabral tears, and (4) minimal to no arthritic changes (all four criteria required). In general, age was not used as a contraindication for surgery. A total of 86% (241 of 281) of patients older than 40 and 91% (494 of 544) of those younger than 40 were available for minimum of 2 years' follow-up, had complete datasets (radiographs as well as preoperative and most recent patient-reported outcomes scores) at a minimum of 2 years after surgery, and were considered eligible for the match. Propensity score matching was used to match for BMI, gender, preoperative symptomatic period, surgeon experience, Tönnis grade, and degree of intraoperative chondral lesion. We matched at a 1:2 ratio 130 patients older than age 40 with 260 patients younger than age 40. The mean ± SD follow-up duration for both groups was 5 ± 2 years. The mean age of the cohort of interest was 47 ± 5 years compared with 28 ± 7 years in the control. Fifty-four percent (70 of 130) of patients older than 40 years were women and 46% (60 of 130) were men; for those younger than 40, 51% (133 of 260) of participants were women and 49% (127 of 260) were men. Tönnis grade distribution for patients older than 40 was as follows: 46% (60 of 130) had Grade 0, 42% (55 of 130) had Grade 1, and 12% (15 of 130) had Grade 2. In comparison, Tönnis grade for patients younger than 40 was as follows: 52% (136 of 260) had Grade 0, 38% (100 of 260) had Grade 1, and 9% (24 of 260) had Grade 2 (p = 0.49). Chondral lesion degree was determined intraoperatively as none, a partial-thickness tear, or a full-thickness tear. Tönnis grade was determined based on preoperative plain AP hip radiographs. We then compared the percentage of patients who converted to THA during the surveillance period (our primary study outcome). We also compared the difference in delta (preoperative minus postoperative) improvement in functional outcome scores using the modified Harris Hip Score (mHHS) between the groups, excluding those who had already been converted to THA.

RESULTS

In patients older than 40 years, 16% (21 of 130) converted to THA at a mean time to conversion of 2 ± 1 years compared with 7% (17 of 260) at a mean time of 2 ± 2 years in patients younger than 40 years (p = 0.01). At a mean of 5 ± 2 years after FAO, among those patients who had not undergone conversion to THA, the mean delta mHHS score for patients older than 40 was 11 ± 17, compared with 20 ± 26 for patients younger than 40 (p = 0.04).

CONCLUSION

Since approximately 1 in 6 patients older than 40 years in this series who underwent FAO for FAI opted for early conversion to THA at a mean time of 2 years after the osteoplasty procedure, and the remaining patients who did not undergo THA reported lower improvement in functional outcomes, we recommend surgeons avoid this procedure in patients in this age group until or unless we can better refine our indications. This is especially true because loss to follow-up causes us to believe that, if anything, our estimates of the risk of conversion to THA are conservative.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Can the Femoro-Epiphyseal Acetabular Roof (FEAR) Index Be Used to Distinguish Dysplasia from Impingement?

BACKGROUND

Classifying hips with structural deformity on the spectrum from impingement to dysplasia is often subjective and frequently inexact. Currently used radiographic measures may inaccurately predict a hip's morphological stability in borderline hips. A recently described radiographic measure, the Femoro-Epiphyseal Acetabular Roof (FEAR) index, has demonstrated an ability to predict stability in the borderline hip. This measure is attractive to clinicians because procedures can be used on the basis of a hip's pathomechanics. This study was designed to further validate and characterize the FEAR index in a skeletally immature population, in hips with dysplasia/femoroacetabular impingement (FAI), and in asymptomatic hips.

QUESTIONS/PURPOSES

(1) What are the characteristics of the FEAR index in children and how does the index change with skeletal maturation? (2) How does the FEAR index correlate with clinical diagnosis and surgical treatment in a large cohort of symptomatic hips and asymptomatic controls? (3) How does the FEAR index correlate with clinical diagnosis in the borderline hip (lateral center-edge angle [LCEA] 20°-25°) group?

METHODS

A total of 220 participants with symptomatic investigational hips with a clinical diagnosis of dysplasia or FAI between January 2008 and January 2018 were retrospectively collected from the senior author's practice. Investigational hips were excluded if they had any femoral head abnormalities preventing LCEA measurement (for example, Perthes disease), Tönnis osteoarthritis grade greater than 1, prior hip surgery, or prior femoral osteotomy. In the 220 participants, 395 hips met inclusion criteria. Once exclusion criteria were applied, 15 hips were excluded due to prior hip surgery or prior femoral osteotomy, and 12 hips were excluded due to femoral head deformity. A single hip was then randomly selected from each participant, resulting in 206 investigational hips with a mean age of 13 ± 3 years. Between January 2017 and December 2017, 70 asymptomatic control participants were retrospectively collected from the senior author's institutional trauma database. Control hips were included if the AP pelvis film had the coccyx centered over the pubic symphysis and within 1 to 3 cm of the superior aspect of the symphysis. Control hips were excluded if there was any fracture to the pelvis or ipsilateral femur or the participant had prior hip/pelvis surgery. After exclusion criteria were applied, 16 hips were excluded due to fracture. One hip was then randomly selected from each participant, resulting in 65 control hips with a mean age of 16 ± 8 years. Standardized standing AP pelvis radiographs were used to measure the FEAR index, LCEA, and Tönnis angle in the investigational cohort. Standardized false-profile radiographs were used to measure the anterior center-edge angle (ACEA) in the investigational cohort. Two blinded investigators measured the FEAR index with an intraclass correlation coefficient of 0.92 [95% CI 0.84 to 0.96]. Question 1 was answered by comparing the above radiographic measures in age subgroups (childhood: younger than 10 years; adolescence: 10 to 14 years old; maturity: older than 14 years) of dysplastic, FAI, and control hips. Question 2 was answered by comparing the radiographic measures in all dysplastic, FAI, control hips, and a subgroup of operatively or nonoperatively managed dysplasia and FAI hips. Question 3 was answered by comparing the radiographic measures in borderline (LCEA 20°-25°) dysplastic, FAI, and control hips.

RESULTS

The FEAR index was lower in older dysplastic of hips (younger than 10 years, 6° ± 9°; 10 to 14 years, 4° ± 10°; older than 14 years, 5° ± 9°; p < 0.001) and control hips (younger than 10 years, -6° ± 5°; 10 to 14 years, -15° ± 4°; older than 14 years, -16° ± 7°; p < 0.001). The diagnosis and age groups were independently correlated with the FEAR index (p < 0.001). The relationship between the FEAR index and diagnosis remained consistent in each age group (p = 0.11). The FEAR index was higher in all dysplastic hips (mean 5° ± 10°) than in asymptomatic controls (mean -13° ± 7°; p < 0.001) and FAI hips (mean -10° ± 11°; p < 0.001). Using -1.3° as a cutoff for FAI/control hips and dysplastic hips, 81% (112 of 139) of hips with values below this threshold were FAI/control, and 89% (117 of 132) of hips with values above -1.3° were dysplastic. The receiver operator characteristics area under the curve (ROC-AUC) was 0.91. Similarly, the FEAR index was higher in borderline dysplastic hips than in both asymptomatic borderline controls (p < 0.001) and borderline FAI hips (p < 0.001). Eighty-nine percent (33 of 37) of hips with values below this threshold were FAI/control, and 90% (37 of 41) of hips with values above -1.3° were dysplastic. The ROC-AUC for borderline hips was 0.86.

CONCLUSION

The FEAR index was associated with the diagnosis of hip dysplasia and FAI in a patient cohort with a wide age range and with varying degrees of acetabular deformity. Specifically, a FEAR index greater than -1.3° is associated with a dysplastic hip and a FEAR index less than -1.3° is associated with a hip displaying FAI. Using this reliable, developmentally based radiographic measure may help hip preservation surgeons establish a correct diagnosis and more appropriately guide treatment.

LEVEL OF EVIDENCE LEVEL

III, diagnostic study.

What Mid-term Patient-reported Outcome Measure Scores, Reoperations, and Complications Are Associated with Concurrent Hip Arthroscopy and Periacetabular Osteotomy to Treat Dysplasia with Associated Intraarticular Abnormalities?

BACKGROUND

Periacetabular osteotomy (PAO) is a well-accepted treatment for acetabular dysplasia, but treatment success is not uniform. Concurrent hip arthroscopy has been proposed for select patients to address intraarticular abnormalities. The patient-reported outcomes, complications, and reoperations for concurrent arthroscopy and PAO to treat acetabular dysplasia remain unclear.

QUESTIONS/PURPOSES

(1) What are the functional outcome scores among select patients treated with PAO plus concurrent hip arthroscopy at mid-term follow-up? (2) What factors are associated with conversion to THA or persistent symptoms (modified Harris hip score ≤ 70 or WOMAC pain subscore ≥ 10)? (3) What proportion of patients underwent further hip preservation surgery at mid-term follow-up? (4) What are the complications associated with the procedure?

METHODS

Between November 2005 and December 2012, 78 patients (81 hips) who presented with symptomatic acetabular dysplasia-defined as a lateral center-edge angle less than 20° with hip pain for more than 3 months that interfered with daily function-had undergone unsuccessful nonsurgical treatment, had associated intraarticular abnormalities on MRI, and underwent combined hip arthroscopy and PAO. Eleven patients did not have minimum 4-year follow-up and were excluded, leaving 67 patients (70 hips) who met our inclusion criteria and had a mean follow-up duration of 6.5 ± 1.6 years. We retrospectively evaluated patient-reported outcomes at final follow-up using the University of California Los Angeles (UCLA) activity score, the modified Harris Hip Score (mHHS), and the WOMAC pain subscore. Conversion to THA or persistent symptoms were considered clinical endpoints. Repeat surgical procedures were drawn from a prospectively maintained database, and major complications were graded according to the validated Clavien-Dindo classification (Grade III or IV). Student t-tests, chi-square tests, and Fisher exact tests identified the association of patient factors, radiographic measures, and surgical details with clinical endpoints. For patients who underwent bilateral procedures, only the first hip was included in our analyses.

RESULTS

At final follow-up, the mean mHHS for all patients improved from a mean ± SD of 55 ± 19 points to 85 ± 17 points (p < 0.001), the UCLA activity score improved from 6.5 ± 2.7 points to 7.5 ± 2.2 points (p = 0.01), and the WOMAC pain score improved from 9.1 ± 4.3 points to 3.2 ± 3.9 points (p < 0.001). Three percent (2 of 67) of patients underwent subsequent THA, while 21% (15 of 70) of hips were persistently symptomatic, defined as mHHS less than or equal to 70 or WOMAC pain subscore greater than or equal to 10. Univariate analyses indicated that no patient demographics, preoperative or postoperative radiographic metrics, or intraoperative findings or procedures were associated with subsequent THA or symptomatic hips. Worse baseline mHHS and WOMAC pain scores were associated with subsequent THA or symptomatic hips. Seven percent (5 of 67) of patients underwent repeat hip preservation surgery for recurrent symptoms, and 4% (3 of 67) of patients had major complications (Clavien-Dindo Grade III or IV).

CONCLUSION

This study demonstrated that concurrent hip arthroscopy and PAO to treat symptomatic acetabular dysplasia (with intraarticular abnormalities) has good clinical outcomes at mid-term follow-up in many patients; however, persistent symptoms or conversion to THA affected almost a quarter of the sample. We noted an acceptable complication profile. Further study is needed to directly compare this approach to more traditional techniques that do not involve arthroscopy. We do not use isolated hip arthroscopy to treat symptomatic acetabular dysplasia.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Medialization of the Hip's Center with Periacetabular Osteotomy: Validation of Assessment with Plain Radiographs

BACKGROUND

Periacetabular osteotomy (PAO) increases acetabular coverage of the femoral head and medializes the hip's center, restoring normal joint biomechanics. Past studies have reported data regarding the degree of medialization achieved by PAO, but measurement of medialization has never been validated through a comparison of imaging modalities or measurement techniques. The ilioischial line appears to be altered by PAO and may be better visualized at the level of the inferior one-third of the femoral head, thus, an alternative method of measuring medialization that begins at the inferior one-third of the femoral head may be beneficial.

QUESTIONS/PURPOSES

(1) What is the true amount and variability of medialization of the hip's center that is achieved with PAO? (2) Which radiographic factors (such as lateral center-edge angle [LCEA] and acetabular inclination [AI]) correlate with the degree of medialization achieved? (3) Does measurement of medialization on plain radiographs at the center of the femoral head (traditional method) or inferior one-third of the femoral head (alternative method) better correlate with true medialization? (4) Are intraoperative fluoroscopy images different than postoperative radiographs for measuring hip medialization?

METHODS

We performed a retrospective study using a previously established cohort of patients who underwent low-dose CT after PAO. Inclusion criteria for this study included PAO as indicated for symptomatic acetabular dysplasia, preoperative CT scan, and follow-up between 9 months and 5 years. A total of 333 patients who underwent PAO from February 2009 to July 2018 met these criteria. Additionally, only patients who were between 16 and 50 years old at the time of surgery were included. Exclusion criteria included prior ipsilateral surgery, femoroacetabular impingement (FAI), pregnancy, neuromuscular disorder, Perthes-like deformity, inadequate preoperative CT, and inability to participate. Thirty-nine hips in 39 patients were included in the final study group; 87% (34 of 39) were in female patients and 13% (5 of 39 hips) were in male patients. The median (range) age at the time of surgery was 27 years (16 to 49). Low-dose CT images were obtained preoperatively and at the time of enrollment postoperatively; we also obtained preoperative and postoperative radiographs and intraoperative fluoroscopic images. The LCEA and AI were assessed on plain radiographs. Hip medialization was assessed on all imaging modalities by an independent, blinded assessor. On plain radiographs, the traditional and alternative methods of measuring hip medialization were used. Subgroups of good and fair radiographs, which were determined by the amount of pelvic rotation that was visible, were used for subgroup analyses. To answer our first question, medialization of all hips was assessed via measurements made on three-dimensional (3-D) CT hip reconstruction models. For our second question, Pearson correlation coefficients, one-way ANOVA, and the Student t-test were calculated to assess the correlation between radiographic parameters (such as LCEA and AI) and the amount of medialization achieved. For our third question, statistical analyses were performed that included a linear regression analysis to determine the correlation between the two radiographic methods of measuring medialization and the true medialization on CT using Pearson correlation coefficients, as well as 95% confidence intervals and standard error of the estimate. For our fourth question, Pearson correlation coefficients were calculated to determine whether using intraoperative fluoroscopy to make medialization measurements differs from measurements made on radiographs.

RESULTS

The true amount of medialization of the hip center achieved by PAO in our study as assessed by reference-standard CT measurements was 4 ± 3 mm; 46% (18 of 39 hips) were medialized 0 to 5 mm, 36% (14 hips) were medialized 5 to 10 mm, and 5% (2 hips) were medialized greater than 10 mm. Thirteen percent (5 hips) were lateralized (medialized < 0 mm). There were small differences in medialization between LCEA subgroups (6 ± 3 mm for an LCEA of ≤ 15°, 4 ± 4 mm for an LCEA between 15° and 20°, and 2 ± 3 mm for an LCEA of 20° to 25° [p = 0.04]). Hips with AI ≥ 15° (6 ± 3 mm) achieved greater amounts of medialization than did hips with AI of < 15° (2 ± 3 mm; p < 0.001). Measurement of medialization on plain radiographs at the center of the femoral head (traditional method) had a weaker correlation than using the inferior one-third of the femoral head (alternative method) when compared with CT scan measurements, which were used as the reference standard. The traditional method was not correlated across all radiographs or only good radiographs (r = 0.16 [95% CI -0.17 to 0.45]; p = 0.34 and r = 0.26 [95% CI -0.06 to 0.53]; p = 0.30), whereas the alternative method had strong and very strong correlations when assessed across all radiographs and only good radiographs, respectively (r = 0.71 [95% CI 0.51 to 0.84]; p < 0.001 and r = 0.80 [95% CI 0.64 to 0.89]; p < 0.001). Measurements of hip medialization made on intraoperative fluoroscopic images were not found to be different than measurements made on postoperative radiographs (r = 0.85; p < 0.001 across all hips and r = 0.90; p < 0.001 across only good radiographs).

CONCLUSION

Using measurements made on preoperative and postoperative CT, the current study demonstrates a mean true medialization achieved by PAO of 4 mm but with substantial variability. The traditional method of measuring medialization at the center of the femoral head may not be accurate; the alternate method of measuring medialization at the lower one-third of the femoral head is a superior way of assessing the hip center's location. We suggest transitioning to using this alternative method to obtain the best clinical and research data, with the realization that both methods using plain radiography appear to underestimate the true amount of medialization achieved with PAO. Lastly, this study provides evidence that the hip center's location and medialization can be accurately assessed intraoperatively using fluoroscopy.

LEVEL OF EVIDENCE

Level III, diagnostic study.

What Are the Early Outcomes of True Reverse Periacetabular Osteotomy for Symptomatic Hip Overcoverage?

BACKGROUND

Acetabular overcoverage is associated with pincer-type femoroacetabular impingement (FAI). A subtype of acetabular overcoverage is caused by a deep acetabulum with a negatively tilted acetabular roof, in which acetabular reorientation may be a preferable alternative to rim trimming to uncover the femoral head. We introduced the true reverse periacetabular osteotomy (PAO) in 2003, which in contrast to an anteverting PAO, also flexes and abducts the acetabulum relative to the intact ilium to decrease anterior and lateral femoral head coverage and correct negative tilt of the acetabular roof. To our knowledge, the clinical results of the true reverse PAO have not been evaluated.

QUESTIONS/PURPOSES

For a group of patients who underwent reverse PAO, (1) Do patients undergoing reverse PAO demonstrate short-term improvement in pain, function, and hip ROM, and decreased acetabular coverage, as defined by lateral and anterior center-edge angle and Tönnis angle? (2) Are there identifiable factors associated with success or adverse outcomes of reverse PAO as defined by reoperation, conversion to THA, or poor patient-reported outcome scores? (3) Are there identifiable factors associated with early complications?

METHODS

Between 2003 and 2017, two surgeons carried out 49 reverse PAOs in 37 patients. Twenty-five patients had unilateral reverse PAO and 12 patients had staged, bilateral reverse PAOs. To ensure that each hip was an independent data point for statistical analysis, we chose to include in our series only the first hip in the patients who had bilateral reverse PAOs. During the study period, our general indications for this operation were symptomatic lateral and anterior acetabular overcoverage causing FAI that had failed to respond to previous conservative or surgical treatment. Thirty-seven hips in 37 patients with a median (range) age of 18 years (12 to 41; interquartile range 16 to 21) were included in this retrospective study at a minimum follow-up of 2 years (median 6 years; range 2 to 17). Thirty-four patients completed questionnaires, 24 patients had radiographic evaluation, and 23 patients received hip ROM clinical examination. However, seven patients had not been seen in more than 5 years. The clinical and radiographic parameters of all 37 hips that underwent reverse PAO in 37 patients from a longitudinally maintained institutional database were retrospectively studied preoperatively and postoperatively. Adverse outcomes were considered conversion to THA or a WOMAC pain score greater than 10 at least 2 years postoperatively. Patient-reported outcomes, radiographic measurements, and hip ROM were evaluated preoperatively and at most recent follow-up using a paired t-test or McNemar test, as appropriate. Linear regression analysis was used to assess for identifiable factors associated with clinical outcomes. Logistic regression analysis was used to assess for identifiable factors associated with adverse outcomes and surgical complications. All tests were two-sided, and p values less than 0.05 were considered significant.

RESULTS

At a minimum of 2 years after reverse PAO, patients experienced improvement in WOMAC pain (-7 [95% CI -9 to -5]; p < 0.001), stiffness (-2 [95% CI -3 to -1]; p < 0.001), and function scores (-18 [95% CI -24 to -12]; p < 0.001) and modified Harris Hip Score (mHHS) (20 [95% CI 13 to 27]; p < 0.001). The mean postoperative hip ROM improved in internal rotation (8° [95% CI 2° to 14°]; p = 0.007). Acetabular coverage, as defined by lateral center-edge angle (LCEA), anterior center-edge angle (ACEA), and Tönnis angle, improved by -8° (95% CI -12° to -5°; p < 0.001) for LCEA, -12° (95% CI -15° to -9°; p < 0.001) for ACEA, and 9° (95% CI 6° to 13°; p < 0.001) for Tönnis angle. The postoperative severity of radiographic arthritis was associated with worse WOMAC function scores such that for each postoperative Tönnis grade, WOMAC function score increased by 12 points (95% CI 2 to 22; p = 0.03). A greater postoperative Tönnis grade was also correlated with worse mHHS, with an average decrease of 12 points (95% CI -20 to -4; p = 0.008) in mHHS for each additional Tönnis grade. Presence of a positive postoperative anterior impingement test was associated with a decrease in mHHS score at follow-up, with an average 23-point decrease in mHHS (95% CI -34 to -12; p = 0.001). Nineteen percent (7 of 37) of hips had surgery-related complications. Four hips experienced adverse outcomes at final follow-up, with two patients undergoing subsequent THA and two with a WOMAC pain score greater than 10. We found no factors associated with complications or adverse outcomes.

CONCLUSION

The early clinical and radiographic results of true reverse PAO compare favorably to other surgical treatments for pincer FAI, suggesting that reverse PAO is a promising treatment for cases of pincer FAI caused by global acetabular overcoverage. However, it is a technically complex procedure that requires substantial training and preparation by a surgeon who is already familiar with standard PAO, and it must be carefully presented to patients with discussion of the potential risks and benefits. Future studies are needed to further refine the indications and to determine the long-term outcomes of reverse PAO.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Prominent Anterior Inferior Iliac Spine Morphologies Are Common in Patients with Acetabular Dysplasia Undergoing Periacetabular Osteotomy

BACKGROUND

The anterior inferior iliac spine (AIIS) prominence is increasingly recognized in the setting of femoroacetabular impingement (FAI). The AIIS prominence may contribute to decreased hip flexion after acetabular reorientation in patients with acetabular dysplasia. AIIS morphologies have been characterized in numerous populations including asymptomatic, FAI, and athletic populations, but the morphology of the AIIS in patients with symptomatic acetabular dysplasia undergoing periacetabular osteotomy (PAO) has not been studied. In acetabular dysplasia, deficiency of the anterosuperior acetabular rim is commonly present and may result in the AIIS being positioned closer to the acetabular rim. Understanding morphological variation of the AIIS in patients with symptomatic dysplasia, and its relationship to dysplasia subtype and severity may aid preoperative planning, surgical technique, and evaluation of postoperative issues after PAO.

QUESTIONS/PURPOSES

In this study, we sought to determine: (1) the variability of AIIS morphology types in hips with symptomatic acetabular dysplasia and (2) whether the differences in the proportion of AIIS morphologies are present between dysplasia pattern and severity subtypes.

METHODS

Using our hip preservation database, we identified 153 hips (148 patients) who underwent PAO from October 2013 to July 2015. Inclusion criteria for the current study were (lateral center-edge angle [LCEA] < 20°), Tönnis Grade of 0 or 1 on plain AP radiographs of the pelvis, preoperative low-dose CT scan, and no prior surgery, trauma, neuromuscular, ischemic necrosis, or Perthes-like deformity. A total of 50 patients (50 hips) with symptomatic acetabular dysplasia undergoing evaluation for surgical planning of PAO remained for retrospective evaluation; we used these patients' low-dose CT scans for analysis. The median (range) age of patients in the study was 24 years (13 to 49). Ninety percent (45 of 50) of the hips were in female patients, whereas 10% (5 of 50) were in male patients. The morphology of the AIIS was classified on three-dimensional CT reconstructions according to a previously published classification to define the relationship between the AIIS and the acetabular rim. The morphology of the AIIS was classified as Type I (AIIS well proximal to acetabular rim), Type II (AIIS extending to level of acetabular rim), or Type III (AIIS extending distal to acetabular rim). Acetabular dysplasia subtype was characterized according to a prior protocol as either predominantly an anterosuperior acetabular deficiency, a posterosuperior acetabular deficiency, or a global acetabular deficiency. Acetabular dysplasia severity was distinguished as mild (LCEA 15° to 20°) or moderate/severe (LCEA < 15°). To answer our first question, regarding the proportions of each AIIS morphology in the dysplasia population, we calculated proportions and 95% CI estimates. To answer our second question, regarding the proposition of AIIS type between subtypes of dysplasia type and severity, we used a chi-square test or Fisher's exact test to compare categorical variables. A p value of < 0.05 was considered significant.

RESULTS

Seventy-two percent (36 of 50; 95% CI 58% to 83%) of patients had a Type II or III AIIS morphology. Type I AIIS morphology was found in 28% of patients (14 of 50; 95% CI 18% to 42%), Type II AIIS morphology in 62% (31 of 50; 95% CI 48% to 74%), and Type III AIIS/morphology in 10% (5 of 50; 95% CI 4% to 21%). A Type I AIIS was seen in seven of 15 of patients with anterosuperior acetabular deficiency, three of 18 of patients with global deficiency, and four of 17 patients with posterosuperior deficiency (p = 0.08). There was no difference in the variability of AIIS morphologies between the different subtypes of acetabular dysplasia pattern and no difference in AIIS morphology variability between patients with mild versus moderate/severe dysplasia.

CONCLUSIONS

The morphology of the AIIS in patients with acetabular dysplasia is commonly prominent, with 72% of hips having Type II or Type III morphologies.

CLINICAL RELEVANCE

The AIIS is often prominent in patients with acetabular dysplasia undergoing PAO, regardless of dysplasia pattern or severity. Prominent AIIS morphologies may affect hip flexion ROM after acetabular reorientation. AIIS morphology is a variable that should be considered during preoperative planning for PAO. Future studies are needed to assess the clinical significance of a prominent AIIS on intraoperative findings and postoperative status after PAO.

The Acetabular Wall Index Is Associated with Long-term Conversion to THA after PAO

BACKGROUND

Periacetabular osteotomy (PAO) has been shown to be a valuable option for delaying the onset of osteoarthritis in patients with hip dysplasia. Published studies at 30 years of follow-up found that postoperative anterior overcoverage and posterior undercoverage were associated with early conversion to THA. The anterior and posterior wall indices are practical tools for assessing AP coverage on standard AP radiographs of the pelvis pre-, intra-, and postoperatively. However, no study that we know of has evaluated the relationship between the postoperative anterior and posterior wall indices and survivorship free from arthroplasty.

QUESTIONS/PURPOSES

In a study including patients after PAO for developmental dysplasia of the hip (DDH), we evaluated whether the acetabular wall index is associated with conversion to THA in the long-term after PAO. We asked: (1) Is an abnormal postoperative anterior wall index associated with conversion to THA after PAO? (2) Is an abnormal postoperative posterior wall index associated with conversion to THA after PAO? (3) Are there other factors associated with joint replacement after PAO?

METHODS

This retrospective study involved pooling data of PAO for DDH from two previously published sources. The first series (1984-1987) comprised the very first 75 PAOs for symptomatic DDH performed at the inventor's institution. The second (1997-2000) comprised a series of PAOs for symptomatic DDH completed at the same institution 10 years later. No patient was lost to follow-up. Fifty hips (44 patients) were excluded for predefined reasons (previous surgery, substantial femoral pathomorphologies, poor-quality radiographs), leaving 115 hips (102 patients, mean age 29 ± 11 years, 28% male) for analysis with a mean follow-up of 22 ± 6 years. One observer not involved in patient treatment digitally measured the anterior and posterior wall indices on postoperative AP pelvic radiographs of all patients. All patients were contacted by mail or telephone to confirm any conversion to THA and the timing of that procedure relative to the index procedure. We performed univariate and multivariate Cox regression analyses using conversion to THA as our endpoint to determine whether the anterior and posterior wall indices are associated with prosthetic replacement in the long-term after PAO. Thirty-one percent (36 of 115) of hips were converted to THA within a mean of 15 ± 7 years until failure. The mean follow-up duration of the remaining patients was 22 ± 6 years.

RESULTS

A deficient anterior wall index was associated with conversion THA in the long-term after PAO (adjusted hazard ratio 10 [95% CI 3.6 to 27.9]; p < 0.001). Although observed in the univariate analysis, we could not find a multivariate association between the posterior wall index and a higher conversion rate to THA. Grade 0 Tönnis osteoarthritis was associated with joint preservation (adjusted HR 0.2 [95% CI 0.07 to 0.47]; p = 0.005). Tönnis osteoarthritis Grades 2 and 3 were associated with conversion to THA (adjusted HR 2.3 [95% CI 0.9 to 5.7]; p = 0.08).

CONCLUSION

A deficient anterior wall index is associated with a decreased survivorship of the native hip in the long-term after PAO. Intraoperatively, in addition to following established radiographical guidelines, the acetabular wall indices should be measured systematically to ascertain optimal acetabular fragment version to increase the likelihood of reconstructive survival after PAO for DDH.

LEVEL OF EVIDENCE

Level III, therapeutic study.

The Effect of Postural Pelvic Dynamics on the Three-dimensional Orientation of the Acetabular Cup in THA Is Patient Specific

BACKGROUND

Sagittal pelvic dynamics mainly consist of the pelvis rotating anteriorly or posteriorly while the hips flexes, and this affects the femoroacetabular or THA configuration. Thus far, it is unknown how the acetabular cup of the THA in the individual patient reorients with changing sagittal pelvic dynamics.

QUESTIONS/PURPOSES

The aim of this study was to validate a method that establishes the three-dimensional (3-D) acetabular cup orientation with changing sagittal pelvic dynamics and describe these changes during functional pelvic dynamics.

METHODS

A novel trigonometric mathematical model, which was incorporated into an easy-to-use tool, was tested. The model connected sagittal tilt, transverse version, and coronal inclination of the acetabular cup during sagittal pelvic tilt. Furthermore, the effect of sagittal pelvic tilt on the 3-D reorientation of acetabular cups was simulated for cups with different initial positions. Twelve pelvic CT images of patients who underwent THA were taken and rotated around the hip axis to different degrees of anterior and posterior sagittal pelvic tilt (± 30°) to simulate functional pelvic tilt in various body positions. For each simulated pelvic tilt, the transverse version and coronal inclination of the cup were manually measured and compared with those measured in a mathematical model in which the 3-D cup positions were calculated. Next, this model was applied to different acetabular cup positions to simulate the effect of sagittal pelvic dynamics on the 3-D orientation of the acetabular cup in the coronal and transverse plane. After pelvic tilt was applied, the intraclass correlation coefficients of 108 measured and calculated coronal and transverse cup orientation angles were 0.963 and 0.990, respectively, validating the clinical use of the mathematical model.

RESULTS

The changes in 3-D acetabular cup orientation by functional pelvic tilt differed substantially between cups with different initial positions; the change in transverse version was much more pronounced in cups with low coronal inclination (from 50° to -29°) during functional pelvic tilt than in cups with a normal coronal inclination (from 39° to -11°) or high coronal inclination (from 31° to 2°). However, changes in coronal inclination were more pronounced in acetabular cups with high transverse version.

CONCLUSION

Using a simple algorithm to determine the dynamic 3-D reorientation of the acetabular cup during functional sagittal pelvic tilt, we demonstrated that the 3-D effect of functional pelvic tilt is specific to the initial acetabular cup orientation and thus per THA patient.

CLINICAL RELEVANCE

Future studies concerning THA (in)stability should not only include the initial acetabular cup orientation, but also they need to incorporate the effect of sagittal pelvic dynamics on the individual 3-D acetabular cup orientation. Clinicians can also use the developed tool, www.3d-hip.com, to calculate the acetabular cup's orientation in other instances, such as for patients with spinopelvic imbalance.

What Are the Long-term Results of Cemented Revision THA with Use of Both Acetabular and Femoral Impaction Bone Grafting in Patients Younger Than 55 Years?

BACKGROUND

The increasing number of THAs in younger patients will inevitably result in an increase of revision procedures. However, there is little evidence about the outcome of revision procedures in this patient group. Therefore, we updated a previous study conducted 5 years ago about the outcome of revision procedures in patients younger than 55 years.

QUESTIONS/PURPOSES

We sought to provide a concise update on the previously reported (1) long-term failure rate as defined by repeat revision, (2) clinical outcome as defined by the Oxford Hip score and the Harris Hip score, and (3) radiographic outcome of cemented revision THA performed with impaction bone grafting on both the acetabular and femoral sides in one surgery in patients younger than 55 years old.

METHODS

Between 1991 and 2007, we performed 86 complete THA revisions in patients younger than 55 years. In 38% (33 of 86) of revisions, bone impaction grafting was used on both the acetabular and femoral side because of acetabular and femoral bone stock loss. Mean age at time of revision was 46 ± 8 years. No patient was lost to follow-up, but six patients died during follow-up, including three since 2015. Still, the hips of all 33 patients were included in analysis at a mean of 17 ± 5 years. Failure was calculated using competing risk analysis. For clinical outcome, we assessed the Harris Hip score and the Oxford Hip score from our longitudinally maintained institutional database. Radiographic analysis was performed to evaluate radiographic loosening, defined as radiolucencies ≥ 2 mm in all zones or ≥ 5 mm migration for both components. The acetabular component was also considered loose with tilting ≥ 5°.

RESULTS

The 15-year failure rate of revision THA was 27% (95% CI 13 to 44) for re-revision of any component for any reason and 10% (95% CI 3 to 25) for re-revision of any component for aseptic loosening. The mean Harris Hip score increased from 55 ± 18 preoperatively to 74 ± 22 at latest follow-up. Eight cups were considered radiographically loose, seven of which were re-revised. No stems were considered radiographically loose. Failure rate with endpoint radiographic loosening at 15 years was 23% (95% CI 10 to 39).

CONCLUSION

We found that impaction bone grafting with a cemented cup and a cemented stem is a valuable biological revision technique that results in a stable and durable solution, after one or even multiple previous revision THAs. Although current implants may prove sufficient in most cases, they do not promote bone stock preservation. We believe that in young patients with bone stock loss, impaction bone grafting can be used as long as the defect can be contained adequately with a metal mesh and viable bone bed is available for revascularization.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

In Vivo Reconstruction of the Acetabular Bone Defect by the Individualized Three-Dimensional Printed Porous Augment in a Swine Model

METHODS

As an acetabular bone defect model created in Bama miniswine, an augment individually fabricated by 3D print technique with Ti6Al4V powders was implanted to repair the defect. Nine swine were divided into three groups, including the immediate biomechanics group, 12-week biomechanics group, and 12-week histological group. The inner structural parameters of the 3D printed porous augment were measured by scanning electron microscopy (SEM), including porosity, pore size, and trabecular diameter. The matching degree between the postoperative augment and the designed augment was assessed by CT scanning and 3D reconstruction. In addition, biomechanical properties, such as stiffness, compressive strength, and the elastic modulus of the 3D printed porous augment, were measured by means of a mechanical testing machine. Moreover, bone ingrowth and implant osseointegration were histomorphometrically assessed.

RESULTS

In terms of the inner structural parameters of the 3D printed porous augment, the porosity was 55.48 ± 0.61%, pore size 319.23 ± 25.05 μm, and trabecular diameter 240.10 ± 23.50 μm. Biomechanically, the stiffness was 21464.60 ± 1091.69 N/mm, compressive strength 231.10 ± 11.77 MPa, and elastic modulus 5.35 ± 0.23 GPa, respectively. Furthermore, the matching extent between the postoperative augment and the designed one was up to 91.40 ± 2.83%. Besides, the maximal shear strength of the 3D printed augment was 929.46 ± 295.99 N immediately after implantation, whereas the strength was 1521.93 ± 98.38 N 12 weeks after surgery (p = 0.0302). The bone mineral apposition rate (μm per day) 12 weeks post operation was 3.77 ± 0.93 μm/d. The percentage bone volume of new bone was 22.30 ± 4.51% 12 weeks after surgery.

CONCLUSION

The 3D printed porous Ti6Al4V augment designed in this study was well biocompatible with bone tissue, possessed proper biomechanical features, and was anatomically well matched with the defect bone. Therefore, the 3D printed porous Ti6Al4V augment possesses great potential as an alternative for individualized treatment of severe acetabular bone defects.

Effects of types and degrees of ankylosing spondylitis hip structural damages on post-total hip arthroplasty outcome measurements

To determine the effects of ankylosing spondylitis (AS)-associated hip damages on the outcome measurements after total hip arthroplasty (THA).The medical records of 122 patients with AS (181 hips) who underwent THA were retrospectively reviewed. The mean follow-up was 43.9 (32-129) months. The types and degrees of hip damages were evaluated by preoperative hip X-rays. The patients were grouped according to the satisfaction degree after the operation. Univariable and multivariable statistical analyses were conducted.The intraclass correlation coefficients for the assessment between the 2 reviewers in the study were 0.86 to 0.97. Cox regression showed that femoral head erosion severity had an effect on the recovery time of independent walking without crutches postoperatively (odds ratio = 1.467, 95% confidence interval: 1.050-2.409, P = .025). The mean time to recover independent walking in the severe femoral head erosion group was 7.3 ± 0.9 weeks, which was 4.6 ± 0.4 weeks longer than in the non-severe femoral head erosion group, as confirmed by the log-rank (Mantel-Cox) test (Chi-squared = 11.684, P = .001). The multivariable analysis showed that higher acetabular sclerosis scores correlated with lower postoperative dissatisfaction risk (odds ratio = 0.322, 95% confidence interval: 0.136-0.764). The multiple linear regression analysis showed that postoperative range of motion (ROM) improvement was affected by preoperative ROM of the hip, space narrowing degree, and ceramic-ceramic material for the weight-bearing surface (F = 179.81, P < .001), with preoperative ROM of the hip having the greatest impact.Severe femoral head erosion prolongs the recovery time of independent walking after THA. Acetabular sclerosis is not associated with poor outcomes in patients with AS-associated hip damage undergoing THA.

Reverse augmentation technique in hip revision arthroplasty: a new strategy for the management of acetabular reconstruction

BACKGROUND

The principle of acetabular total hip revision (THR) is based on acetabular reconstruction and restoration of the center of rotation. The use of augmentation in high cranial acetabular defects combined with a cementless revision shell was studied sufficiently. This study aimed to report a case with the use of an augment inside a cementless revision shell as a reverse augmentation technique.

METHODS

We describe the case of an 86-year-old female patient with a massive acetabular defect during second revision for total hip arthroplasty (THA). Two problems occurred: (1) a fixed cemented stem with a nonmodular head size of 33 mm and (2) a high acetabular defect with an elevated rotation center.

RESULTS

With the distraction technique, allograft filling was used to reconstruct the acetabular defect. A cementless revision shell (REDAPT, Smith and Nephew) with a size of 78 mm was used to stabilize the defect. Locking screws placed cranially and distally were used to stabilize the cup for secondary osseointegration. An augment was placed inside the cup to reconstruct the rotation center. A customized polyethylene liner (outer diameter, 54 mm/inner diameter, 33 mm) was positioned below the augment in the revision cup to reconstruct the center of rotation. An 18-month postoperative X-ray analysis showed a stable construct with full secondary osseointegration.

CONCLUSION

This is the first report of an augment used for a reverse technique inside a cementless shell to restore the center of rotation with the use of a customized polyethylene liner. This might be a reliable option for reconstruction of the center of rotation in large cementless revision cups in acetabular Paprosky type III defects. This technical note shows the possibility of using an augment as a reverse technique in a cementless revision cup.

Effect of sagittal pelvic tilt on joint stress distribution in hip dysplasia: A finite element analysis

BACKGROUND

Physiologic pelvic tilt can change acetabular orientation and coverage in patients with hip dysplasia. In this study, we aimed to clarify the impact of change in sagittal pelvic tilt on joint stress distribution in dysplastic hips.

METHODS

We developed patient-specific finite element models of 21 dysplastic hips and 21 normal hips. The joint contact area, contact pressure, and equivalent stress of the acetabular cartilage were assessed at three pelvic tilt positions relative to the functional pelvic plane: 10° anterior tilt, no tilt, and 10° posterior tilt.

FINDINGS

The mean contact area was 0.6-0.7 times smaller, the mean maximum contact pressure was 1.8-1.9 times higher, and the mean maximum equivalent stress was 1.3-2.8 times higher in dysplastic hips than in normal hips at all three pelvic positions. As the pelvis tilted from 10° anterior to 10° posterior, the mean contact area decreased, and the mean maximum contact pressure and median maximum equivalent stress increased. The latter two changes were more significant in dysplastic hips than in normal hips (total increment was 1.3 MPa vs. 0.4 MPa, P = 0.001, and 3.6 MPa vs. 0.4 MPa, P < 0.001, respectively). The mean equivalent stress increased in the anterosuperior acetabulum during posterior pelvic tilt in dysplastic and normal hips, while the change was not significant in the superior and posterosuperior acetabulum in both groups.

INTERPRETATION

Sagittal pelvic tilt alters the loading environment and joint stress distribution of the hip joint and may impact the degeneration process in dysplastic hips.

Correction of the acetabular index is more crucial than the type of acetabuloplasty in developmental dysplasia

BACKGROUND

Acetabular remodeling may not be predictable after open reduction in developmental dysplasia of the hip (DDH) in older children. Several acetabuloplasties have been developed, and all are aimed at correcting the dysplastic acetabulum. The goal of this study is to evaluate if the type of pelvic acetabuloplasty and the corrected (postoperative) acetabular index (AI) affect early follow-up femoral head coverage.

METHODS

A retrospective review of single-surgeon consecutive acetabuloplasties (Dega or Pemberton) from December 2012 to December 2015 was conducted. The inclusion criteria were a diagnosis of DDH, undergoing simultaneous primary open reduction, and follow-up of at least 18 months. Univariable analysis was based on the type of acetabuloplasty. The correlation between AI and final center edge angle (CEA) was tested. Multiple regression was performed.

RESULTS

Of the total 58 hips in 39 patients included, 41 underwent Dega acetabuloplasty, and 17 had Pemberton acetabuloplasty. The median follow-up was 40.50 months (interquartile range 27.25-57). Pemberton acetabuloplasty produced a lower corrected AI, but the difference was not significant in follow-up measurements. Corrected AI was significantly correlated with final CEA (R = - 0.31, P = 0.018). In the multiple regression, only corrected AI was independently associated with final CEA (B = - 0.29, SE = 0.15, P = 0.06), whereas the type of acetabuloplasty, age, and preoperative severity of the dislocation were not.

CONCLUSION

The correction obtained during acetabuloplasty affects early follow-up femoral head coverage. Ensuring proper sizing and placement of the grafted bone is probably more important than the type of acetabuloplasty chosen.

LEVEL OF EVIDENCE

Level III.

The Hip-Spine Relationship Simplified

Much attention has recently been focused on the relationship between the hip and spine and its contribution to postoperative instability following total hip arthroplasty. However, the terminology can be confusing. Through an understanding of spinopelvic parameters, spinopelvic motion, and the interplay between the spine and pelvis, the surgeon can plan for and decrease the risk of instability after total hip arthroplasty. This review details spinopelvic parameters that predispose to instability and guides readers in understanding spinopelvic motion as it relates to THA instability.

Quantitative assessment of acetabular bone defects: A study of 50 computed tomography data sets

Objectives

Acetabular bone defect quantification and classification is still challenging. The objectives of this study were to suggest and define parameters for the quantification of acetabular bone defects, to analyze 50 bone defects and to present the results and correlations between the defined parameters.

Methods

The analysis was based on CT-data of pelvises with acetabular bone defects and their reconstruction via a statistical shape model. Based on this data, bone volume loss and new bone formation were analyzed in four sectors (cranial roof, anterior column, posterior column, and medial wall). In addition, ovality of the acetabulum, lateral center-edge angle, implant migration, and presence of wall defects were analyzed and correlations between the different parameters were assessed.

Results

Bone volume loss was found in all sectors and was multidirectional in most cases. Highest relative bone volume loss was found in the medial wall with median and [25, 75]—percentile values of 72.8 [50.6, 95.0] %. Ovality, given as the length to width ratio of the acetabulum, was 1.3 [1.1, 1.4] with a maximum of 2.0, which indicated an oval shape of the defect acetabulum. Lateral center-edge angle was 30.4° [21.5°, 40.4°], which indicated a wide range of roof coverage in the defect acetabulum. Total implant migration was 25.3 [14.8, 32.7] mm, whereby cranial was the most common direction. 49/50 cases showed a wall defect in at least one sector. It was observed that implant migration in cranial direction was associated with relative bone volume loss in cranial roof (R = 0.74) and ovality (R = 0.67).

Conclusion

Within this study, 50 pelvises with acetabular bone defects were successfully analyzed using six parameters. This could provide the basis for a novel classification concept which would represent a quantitative, objective, unambiguous, and reproducible classification approach for acetabular bone defects.

Bone density changes following surgical correction of femoroacetabular impingement deformities

OBJECTIVE

Femoroacetabular impingement (FAI) involves abnormal hip biomechanics due to deformities and is associated with osteoarthritis. Bone mineral density (BMD) in the acetabulum is higher in subjects with convex femoral (cam) FAI deformities compared to control subjects. The objective of this study was to assess post-operative changes of BMD with and without surgical correction of the cam deformity.

DESIGN

Thirteen patients with bilateral cam deformities but unilateral symptoms underwent pre-operative and follow-up computed tomography (CT) scans of both hips. The deformity was surgically removed from the symptomatic hip. BMD was measured in regions of interest (ROI) around the superior acetabulum from CT scans at both time points. The contralateral untreated hip was used as a within-patient control. Changes in BMD were assessed by two-way repeated measures ANOVA (side, time) and paired t-tests.

RESULTS

A greater BMD decrease was seen in the treated compared to the untreated hip (P < 0.0018). BMD within the superior acetabulum decreased by 39 mg/cc on the treated side (P < 0.0001) but only 9 mg/cc (P = 0.15) in the untreated contralateral hip. These changes represent 7.1% and 1.7% of the pre-operative BMD on the respective sides.

CONCLUSIONS

BMD decreased in the treated hip, suggesting a positive effect of surgical correction in relieving stresses within the hip joint. Longer term follow-up is required to assess the ultimate fate of the articular cartilage within the joint. This study showed that surgical correction of the cam deformity in patients with FAI may alter the pathological biomechanics within the joint.

Patient-specific parameterised cam geometry in finite element models of femoroacetabular impingement of the hip

BACKGROUND

Impingement resulting in soft tissue damage has been observed in hips with abnormal morphologies. Geometric parameterisation can be used to automatically generate a range of bone geometries for use in computational models, including femurs with cam deformity on the femoral neck.

METHODS

This study verified patient-specific parametric finite element models of 20 patients with cam deformity (10 female, 10 male) through comparison to their patient-specific segmentation-based equivalents. The parameterisation system was then used to generate further models with parametrically defined geometry to investigate morphological changes in both the femur and acetabulum and their effects on impingement.

FINDINGS

Similar findings were observed between segmentation-based and parametric models when assessing soft tissue strains under impingement conditions, resulting from high flexion and internal rotations. Parametric models with cam morphology demonstrated that clinically used alpha angles should not be relied on for estimating impingement severity since planar views do not capture the full three-dimensional geometry of the joint. Furthermore, the parametric approach allowed study of labral shape changes, indicating higher strains can result from bony overcoverage.

INTERPRETATION

The position of cams, as well as their size, can affect the level of soft tissue strain occurring in the hip. This highlights the importance of reporting the full details of three-dimensional geometry used when developing computational models of the hip joint and suggests that it could be beneficial to stratify the patient population when considering treatment options, since certain morphologies may be at greater risk of elevated soft tissue strain.

MRI appearance in the early stage of Legg-Calvé-Perthes disease to predict lateral pillar classification: A retrospective analysis of the labral horizontalization

BACKGROUND

The Herring lateral pillar classification is widely used for the classification of Legg-Calvé-Perthes disease, but is not applied at the early stage of Legg-Calvé-Perthes disease because it is typically applied at the late fragmentation stage. The purpose of this study was to investigate the correlation between the early appearance on magnetic resonance imaging of the acetabular labrum and lateral pillar involvement in Legg-Calvé-Perthes disease.

METHODS

Non-contrast magnetic resonance images of 26 hips in 25 children with early-stage Legg-Calvé-Perthes disease were retrospectively reviewed. The extent of labral horizontalization was quantitatively evaluated with a new method, the labral angle, on T2*-weighted magnetic resonance images. A small labral angle indicates strong labral horizontalization. Calculation of the teardrop distance and acetabular head index on radiographs was modified for application to magnetic resonance imaging, and the extent of cartilaginous lateral subluxation (cartilaginous tear drop distance) and cartilaginous lateral extrusion (cartilaginous acetabular head index) were evaluated. The outcome measure was the lateral pillar classification.

RESULTS

There were statistically significant correlations between the labral angle and the cartilaginous tear drop distance (p = 0.002, ɤ = -0.58) and the cartilaginous acetabular head index (p < 0.001, ɤ = 0.65) on magnetic resonance images. The labral angle was small in order of groups C, B, and A, and there were significant differences between groups A and C (p < 0.001) and B and C (p = 0.006).

CONCLUSION

Greater labral horizontalization observed on magnetic resonance imaging at the early stage of Legg-Calvé-Perthes disease correlated with strong cartilaginous lateral subluxation and extrusion, and with increased lateral pillar collapse at the maximum fragmentation stage. Our finding suggests that a quantitative evaluation of labral horizontalization using magnetic resonance imaging in the early-stage of Legg-Calvé-Perthes disease can predict the later lateral pillar classification.

Acetabular Wall Indices Help to Distinguish Acetabular Coverage in Asymptomatic Adults With Varying Morphologies

BACKGROUND

The anterior wall index (AWI) and posterior wall index (PWI) have been proposed to quantify anterior and posterior acetabular coverage using AP pelvic radiographs. However, these indices have only been reported in symptomatic patients with apparent pathomorphologies (dysplasia, overcoverage, and retroversion) undergoing osteochondroplasty or reorientation osteotomy.

QUESTIONS

(1) What are the ranges for AWI and PWI from measurements obtained on AP pelvic radiographs of asymptomatic senior athletes with well-functioning hips? (2) Is there a difference between the AWI and PWI in asymptomatic athletes with acetabular morphology consistent with acetabular dysplasia, overcoverage, and retroversion when compared with asymptomatic hips that do not meet the radiographic definitions for those morphologies (controls)?

METHODS

Five hundred five athletes (998 asymptomatic native hips) were independently evaluated by two readers on AP pelvic radiographs for AWI and the PWI after excluding hips with prior surgery, inadequate radiographs, or poor function (modified Harris hip score < 80). Hips with a lateral center-edge angle (LCEA) ≥ 20° and ≤ 38° and without acetabular retroversion, based on a positive crossover sign, were used as controls. Hips were categorized as developmental dysplasia of the hip (DDH; undercoverage) if the LCEA was < 20°. Finally, overcoverage was defined as an LCEA > 38°. The mean age of the athletes was 67 years (range, 50-91 years) and 55% were men. Linear generalized estimating equation regression was used to compare each individual diagnosis (DDH, retroversion, overcoverage) with the controls for both AWI and PWI adjusting for age and sex.

RESULTS

The mean AWI in the study population was 0.36 (range, -0.02 to 0.91). The mean PWI was 1.13 (range, 0.12-1.74). The mean AWI and PWI in controls (n = 740) was 0.35 (range, -0.02 to 0.91) and 1.13 (range, 0.64-1.70), respectively. There were 25 (3%) with DDH in whom the mean AWI was 0.26 (range, 0.05-0.5) and the mean PWI was 1.03 (range, 0.71-1.3). There were 112 (11%) retroverted hips in whom the mean AWI was 0.42 (range, 0.1-0.89) and PWI was 1.02 (range, 0.61-1.5). There were 121 (12%) overcovered hips in whom the mean AWI was 0.43 (range, -0.18 to 0.85) and PWI was 1.22 (0.12-1.74). The AWI in the control hips was no different than that of DDH hips (β -0.06; 95% confidence interval [CI], -0.12 to 0.002; p = 0.059) but was found to be lower than retroverted hips (β 0.08; 95% CI, 0.04-0.11; p < 0.001) and overcovered hips (β 0.05; 95% CI, 0.03-0.08; p < 0.001). The PWI in control hips was greater than that of DDH hips (β -0.08; 95% CI, -0.14 to -0.02; p = 0.013) and retroverted hips (β -0.07; 95% CI, -0.11 to -0.04; p < 0.001) but was less than overcovered hips (β 0.07; 95% CI, 0.04-0.10; p < 0.001).

CONCLUSIONS

The measurements of AWI and PWI in well-functioning, asymptomatic hips may be useful in assessing anterior and posterior acetabular coverage because it was able to distinguish between different types of known pathologic morphology. Despite evidence of these morphologic variances, these senior athletes continued to function at a high level. Thus, the identification of morphologic variance was not consistent with signs of pathology, which further supports that early screening of morphology may not predict the development of symptomatic pathology. Future work should focus on comparing these indices for morphologic variance in both symptomatic and asymptomatic hips to determine whether these measurements can be used in identifying problematic hips and as reference ranges for surgical correction.

LEVEL OF EVIDENCE

Level III, diagnostic study.

What Are the Risk Factors for Revision Surgery After Hip Arthroscopy for Femoroacetabular Impingement at 7-year Followup?

BACKGROUND

In recent years, surgical treatment of symptomatic femoroacetabular impingement (FAI) has been increasingly performed using arthroscopy. Bony pathomorphologies and damage to the labrum as well as cartilage defects can be addressed with comparable results to open surgery with overall less surgery-related complications. Despite the increasing importance of hip arthroscopy, however, reports on midterm clinical and radiographic outcomes and comparison to open surgical hip dislocation are scarce.

QUESTIONS/PURPOSES

(1) What are the clinical and radiographic outcomes at a mean 7-year followup; (2) what is the cumulative 7-year survivorship, using the endpoints of THA, progression of osteoarthritis according to Tönnis, or poor clinical outcome with a Merle d'Aubigné score of less than 15 points, of hips with symptomatic FAI treated arthroscopically; and (3) what factors were associated with revision surgery?

METHODS

Between 2003 and 2008 we performed a total of 62 arthroscopic procedures (60 patients) for FAI. For the same indication, we also performed 571 surgical hip dislocations during that time. Standardized treatment was femoral offset correction, acetabular rim trimming, or both and treatment of labral or chondral defects. An arthroscopic approach was generally used if the pathomorphology was located in the anterosuperior quadrant of the hip and was gradually used for more complex cases. We excluded 10 hips (10 patients) in which the standardized treatment was not achieved and no offset correction or acetabular rim trimming was performed. Of the remaining 52 hips (50 patients), 39 hips underwent isolated femoral offset correction, four hips isolated acetabular rim trimming, and nine hips both procedures. At a mean followup of 7 years (range, 5-11 years), the Merle d'Aubigné clinical score was obtained and plain radiographs were examined (Tönnis grade, heterotopic ossification, lateral center-edge [LCE] angle, acetabular index [AI], extrusion index, alpha angle, and pistol grip deformity). Cumulative survivorship was calculated according to Kaplan-Meier using conversion to THA, progression of osteoarthritis (one or more Tönnis grades), or poor clinical outcome (Merle d'Aubigné score < 15 points) as endpoints. Cox regression analysis was used to identify univariate factors associated with revision surgery.

RESULTS

At last followup we detected a significant but possibly not clinically relevant increase in Merle d'Aubigné scores from preoperative levels to latest followup (14 ± 1 versus 16 ± 2, mean difference 2 points with a 95% confidence interval [95% CI] -3 to 7, p < 0.001). Six hips showed progression of osteoarthritis. Cumulative survivorship (hips free from conversion to THA, progression of osteoarthritis, or poor clinical outcome) of hips treated with hip arthroscopy for FAI at a mean followup of 7 years was 81% (95% CI, 68%-95%). Two patients (two hips, 4%) underwent THA at 7 and 9 years, respectively. An increased preoperative acetabular coverage (LCE angle, AI), increased offset in the superior portion of the femoral neck (pistol grip deformity), and a remaining pistol grip deformity postoperatively were associated with revision surgery. Any treatment of the labrum did not influence the outcome. Factors associated with failure could not be identified.

CONCLUSIONS

In this series of patients with arthroscopic treatment of symptomatic FAI, hip arthroscopy resulted in an intact hip without progression of osteoarthritis and with a Merle d'Aubigné score of ≥ 15 points in 81% of patients at 7-year followup. Increased acetabular coverage and femoral pistol grip deformity were risk factors for revision surgery.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

The Femoro-Epiphyseal Acetabular Roof (FEAR) Index: A New Measurement Associated With Instability in Borderline Hip Dysplasia?

BACKGROUND

The definition of osseous instability in radiographic borderline dysplastic hips is difficult. A reliable radiographic tool that aids decision-making-specifically, a tool that might be associated with instability-therefore would be very helpful for this group of patients.

QUESTIONS/PURPOSES

(1) To compare a new radiographic measurement, which we call the Femoro-Epiphyseal Acetabular Roof (FEAR) index, with the lateral center-edge angle (LCEA) and acetabular index (AI), with respect to intra- and interobserver reliability; (2) to correlate AI, neck-shaft angle, LCEA, iliocapsularis volume, femoral antetorsion, and FEAR index with the surgical treatment received in stable and unstable borderline dysplastic hips; and (3) to assess whether the FEAR index is associated clinical instability in borderline dysplastic hips.

METHODS

We defined and validated the FEAR index in 10 standardized radiographs of asymptomatic controls using two blinded independent observers. Interrater and intrarater coefficients were calculated, supplemented by Bland-Altman plots. We compared its reliability with LCEA and AI. We performed a case-control study using standardized radiographs of 39 surgically treated symptomatic borderline radiographically dysplastic hips and 20 age-matched controls with asymptomatic hips (a 2:1 ratio), the latter were patients attending our institution for trauma unrelated to their hips but who had standardized pelvic radiographs between January 1, 2016 and March 1, 2016. Patient demographics were assessed using univariate Wilcoxon two-sample tests. There was no difference in mean age (overall: 31.5 ± 11.8 years [95% CI, 27.7-35.4 years]; stable borderline group: mean, 32.1± 13.3 years [95% CI, 25.5-38.7 years]; unstable borderline group: mean, 31.1 ± 10.7 years [95% CI, 26.2-35.9 years]; p = 0.96) among study groups. Treatment received was either a periacetabular osteotomy (if the hip was unstable) or, for patients with femoroacetabular impingement, either an open or arthroscopic femoroacetabular impingement procedure. The association of received treatment categories with the variables AI, neck-shaft angle, LCEA, iliocapsularis volume, femoral antetorsion, and FEAR index were evaluated first using Wilcoxon two-sample tests (two-sided) followed by stepwise multiple logistic regression analysis to identify the potential associated variables in a combined setting. Sensitivity, specificity, and receiver operator curves were calculated. The primary endpoint was the association between the FEAR index and instability, which we defined as migration of the femoral head either already visible on conventional radiographs or recentering of the head on AP abduction views, a break of Shenton's line, or the appearance of a crescent-shaped accumulation of gadolinium in the posteroinferior joint space at MR arthrography.

RESULTS

The FEAR index showed excellent intra- and interobserver reliability, superior to the AI and LCEA. The FEAR index was lower in the stable borderline group (mean, -2.1 ± 8.4; 95% CI, -6.3 to 2.0) compared with the unstable borderline group (mean, 13.3 ± 15.2; 95% CI, 6.2-20.4) (p < 0.001) and had the highest association with treatment received. A FEAR index less than 5° had a 79% probability of correctly assigning hips as stable and unstable, respectively (sensitivity 78%; specificity 80%).

CONCLUSIONS

A painful hip with a LCEA of 25° or less and FEAR index less than 5° is likely to be stable, and in such a situation, the diagnostic focus might more productively be directed toward femoroacetabular impingement as a potential cause of a patient's pain, rather than instability.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Reconstruction of the Shallow Acetabulum With a Combination of Autologous Bulk and Impaction Bone Grafting Fixed by Cement

BACKGROUND

Acetabular bone deficiency, especially proximal and lateral deficiency, is a difficult technical problem during primary total hip arthroplasty (THA) in developmental dysplasia of the hip (DDH). We report a new reconstruction method using a medial-reduced cemented socket and additional bulk bone in conjunction with impaction morselized bone grafting (additional bulk bone grafting method).

QUESTIONS/PURPOSES

In a population of patients with acetabular dysplasia undergoing THA using a medial-reduced cemented socket and additional bulk bone with impacted morselized bone grafting, we evaluated (1) the radiographic appearance of bone graft; (2) the proportion of cups that developed loosening and subsequent revision; and (3) clinical results (outcome scores and complications).

METHODS

Forty percent of 330 THAs for DDH performed at one center between 1999 and 2009 were defined as shallow dysplastic hips. The additional bulk bone grafting method was performed on 102 THAs with shallow acetabulum (31% for DDH) at one center between 1999 and 2009. We used this approach and technique for shallow acetabuli when a cup protruded from the lateral acetabular edge in preoperative templating. The other 132 dysplastic hips without bone grafting had THA performed at the same periods and served as a control. Acetabuli were defined as shallow when the depth was less than or equal to one-fifth of the pelvic height (cranial-caudal length on radiograph). The additional bulk bone grafting technique was as follows: the resected femoral head was sectioned at 1 to 2 cm thickness, and a suitable size of the bulk bone graft was placed on the lateral iliac cortex and fixed by poly-L-lactate absorbable screws. Autologous impaction morselized bone grafting, with or without hydroxyapatite granules, was performed along with the implantation of a medial-reduced cemented socket. We defined an "incorporated" graft as remodeling and trabeculation including rounding off of the protruding edge of a graft beyond the socket. Radiographic criteria used for determining loosening were migration or a continuous radiolucent zone between the prosthesis/bone cement and host bone. Clinical outcomes were assessed using the Japanese Orthopaedic Association (JOA) and the Merle d'Aubigne and Postel score; complications were tallied from chart review. The followup was 10 ± 3 years (range, 6-15 years).

RESULTS

One acetabular component (1%) with severe shallow and steep acetabuli showed definite radiographic evidence of loosening and was revised. Clinically, the mean JOA score for the hips treated with additional bulk bone grafting THA in this study improved from 39 ± 10 points preoperatively to 95 ± 5 points postoperatively (p < 0.05, paired t-test). The mean Merle d'Aubigne and Postel score for the hips improved from 7 ± 2 points to 17 ± 1 points (p < 0.05, paired t-test). Complications included a Trendelenburg sign in one hip, dislocation in one, and transient partial sciatic nerve palsy in one. Within 3 years 6 months postoperatively, 101 of 102 additional bulk bone grafting cases showed successful bone remodeling and bone graft reorientation without collapse on radiographs. Partial resorption of the additional bone graft on the lateral side was observed in two hips (2%) with socket abduction angles of < 35°.

CONCLUSIONS

Achieving stable acetabular fixation is often challenging in the dysplastic hip, especially shallow acetabulum, and a variety of techniques have been described. Early results of combining bulk graft with impaction of morselized graft are promising. Although each surgical technique was well established, further investigation for clinical results of a combination of these techniques might be necessary to confirm longer term outcomes.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Managing Acetabular Defects in Total Hip Arthroplasty

With the aging population and rising incidence of primary total joint arthroplasty has come the increasing incidence of revision total hip arthroplasties. One challenge in revision total hip arthroplasty is dealing with acetabular defects. The orthopaedic surgeon who chooses to take on these challenges requires a proper method for the evaluation of these defects as well as an evidence-based treatment algorithm. Initial assessment requires appropriate use and interpretation of imaging modalities such as x-rays and computed tomography. Preoperative planning presupposes knowledge of available approaches and implant options, such as porous coated jumbo cups, modular augments, and cup-cage constructs. Surgical execution necessitates experience in the indications for each type of implant for various types of defects. This review will aid in the understanding of each step of the diagnosis and treatment of acetabular defects in revision total hip arthroplasty.

Effect of General Anesthesia on Preoperative Hip Range of Motion in Patients Undergoing Hip Arthroscopy

The purpose of this study was to investigate the effect of general anesthesia on preoperative passive hip range of motion (ROM) in patients undergoing hip arthroscopy for various indications. A total of 260 consecutive patients undergoing hip arthroscopy were included in this study. Passive hip ROM was evaluated bilaterally in the clinic and subsequently under general anesthesia immediately preoperatively. Demographic variables, including age, height, weight, and clinical diagnosis, were recorded for all patients. Hips with pincer-type femoroacetabular impingement (FAI) and hips with acetabular dysplasia showed a mean increase of 4° and 6°, respectively, in hip external rotation at 90° of hip flexion (ER-90) with induction of anesthesia (P=.018 and P=.021, respectively). In contrast, a statistically significant reduction in hip abduction (2°) and hip flexion (4°) was observed following induction of anesthesia in healthy contralateral hips of patients presenting with unilateral hip pathology (P=.01 and P<.001, respectively). Hip ROM does not change to a clinically significant extent with induction of general anesthesia. Small increases in external rotation in patients with FAI or acetabular dysplasia are within the standard error for ROM measurements. [Orthopedics. 2016; 39(6):e1165-e1169.].

No Benefit After THA Performed With Computer-assisted Cup Placement: 10-year Results of a Randomized Controlled Study

BACKGROUND

Computer-assisted surgery (CAS) for cup placement has been developed to improve the functional results and to reduce the dislocation rate and wear after total hip arthroplasty (THA). Previously published studies demonstrated radiographic benefits of CAS in terms of implant position, but whether these improvements result in clinically important differences that patients might perceive remains largely unknown.

QUESTIONS/PURPOSES

We hypothesized that THA performed with CAS would improve 10-year patient-reported outcomes measured by validated scoring tools, reduce acetabular polyethylene wear as measured using a validated radiological method, and increase survivorship.

METHODS

Sixty patients operated on for a THA between April 2004 and April 2005 were randomized into two groups using either the CAS technique or a conventional technique for cup placement. All patient candidates for a THA with the diagnosis of primary arthritis or avascular necrosis were eligible for the CAS procedure and randomly assigned to the CAS group by the Hospital Informatics Department with use of a systematic sampling method. The patients assigned to the freehand cup placement group were matched for sex, age within 5 years, pathological condition, operatively treated side, and body mass index within 3 points. All patients were operated on through an anterolateral approach (patient in the supine position) using cementless implants. In the CAS group, a specific surgical procedure using an imageless cup positioning computer-based navigation system was performed. There were 16 men and 14 women in each group; mean age was 62 years (range, 24-80 years), and mean body mass index was 25 ± 3 kg/m(2). No patient was lost to followup at 10 years, but five patients have died (two in the CAS group and three in the control group). At the 10-year followup, an independent observer blinded to the type of technique performed patients' evaluation. Cup positioning was evaluated postoperatively using a CT scan in the two groups with results previously published. At 10 years, we assessed subjective functional outcome and quality of life using validated questionnaires (SF-12, Harris hip score [HHS], Hip injury and Osteoarthritis Outcome Score). Wear rate was then evaluated on standardized radiographs using a previously validated semiautomated computer analogic measurement method (dual circle method). Complications and survivorship were compared between groups. With our available sample size, this study had 80% power to detect a difference of 4 points out of 100 on the HHS at the p < 0.05 level.

RESULTS

With the numbers available, we found we found no differences between groups regarding HSS at last followup 95.3 ± 5.9 points (CAS group) versus 96.2 ± 4.5 points, a mean difference of 0.9 points (95% confidence interval [CI], -4.3 to 4.6; p = 0.6). There was no difference between the groups in terms of the mean (± SD) acetabular linear wear at 10 years. The mean wear was 0.71 ± 0.6 mm in the CAS group versus 0.77 ± 0.52 mm in the control group, a mean difference of 0.06 mm (95% CI, -0.1 to 0.2; p = 0.54). With the numbers available, there was no difference between the CAS group and the conventional THA groups in terms of survivorship free from aseptic loosening (100%; 95% CI, 100%-95%, versus 100%; 95% CI, 100%-94%; p = 0.3).

CONCLUSIONS

Our observations suggest that CAS used for cup placement does not confer any substantial advantage in function, wear rate, or survivorship at 10 years after THA. Because CAS is associated with added costs and surgical time, future studies need to identify what clinically relevant advantages it offers, if any, to justify its continued use in THA.

LEVEL OF EVIDENCE

Level II, therapeutic study.

Decreased Lumbar Lordosis and Deficient Acetabular Coverage Are Risk Factors for Subchondral Insufficiency Fracture

Subchondral insufficiency fracture (SIF) of the femoral head occurs in the elderly and recipients of organ transplantation. Osteoporosis and deficient lateral coverage of the acetabulum are known risk factors for SIF. There has been no study about relation between spinopelvic alignment and anterior acetabular coverage with SIF. We therefore asked whether a decrease of lumbar lordosis and a deficiency in the anterior acetabular coverage are risk factors. We investigated 37 patients with SIF. There were 33 women and 4 men, and their mean age was 71.5 years (59-85 years). These 37 patients were matched with 37 controls for gender, age, height, weight, body mass index and bone mineral density. We compared the lumbar lordosis, pelvic incidence, pelvic tilt, sacral slope, acetabular index, acetabular roof angle, acetabular head index, anterior center-edge angle and lateral center-edge angle. Lumbar lordosis, pelvic tilt, sacral slope, lateral center edge angle, anterior center edge angle, acetabular index and acetabular head index were significantly different between SIF group and control group. Lumbar lordosis (OR = 1.11), lateral center edge angle (OR = 1.30) and anterior center edge angle (OR = 1.27) had significant associations in multivariate analysis. Decreased lumbar lordosis and deficient anterior coverage of the acetabulum are risk factors for SIF as well as decreased lateral coverage of the acetabulum.

Rotational Acetabular Osteotomy for Pre- and Early Osteoarthritis Secondary to Dysplasia Provides Durable Results at 20 Years

BACKGROUND

Hip dysplasia is a common cause of secondary osteoarthritis (OA). Periacetabular osteotomy or rotational acetabular osteotomy has been used as joint-preserving procedures. However, only a few reports of long-term results with these operations have been reported.

QUESTIONS/PURPOSES

(1) Would satisfactory clinical and radiographic outcomes be maintained at a mean duration of 20 years after rotational acetabular osteotomy for pre- and early-stage OA; and (2) could we identify risk factors for radiographic progression of OA?

METHODS

Between 1987 and 2001, we treated 159 patients (173 hips) with rotational acetabular osteotomies for the diagnosis of pre-OA or early-stage OA according to the technique of Ninomiya and Tagawa. During that period, our general indications for this approach were age younger than 60 years, center-edge angle less than 20°, and improved femoral head coverage and joint congruency on preoperative AP plain radiographs of the hip in abduction; we did not use this approach when joint congruency was not improved or no widening of the joint space was noted on preoperative AP plain radiographs of the hip in abduction. Of those patients, 21 patients with pre-OA (followup rate: 84% [27 hips]) and 110 patients in the early-stage group (followup rate: 82% [118 hips]) were available at a minimum of 15 years for a total patient group of 131 (followup rate: 82% [145 hips]). The mean age at the time of surgery was 22 years in the pre-OA group and 38 years in the early-stage group. The mean followup was 21 years in the pre-OA group and 20 years in the early-stage group. Clinical evaluation was performed with the Merle d'Aubigne and Postel rating scale, and radiographic analyses included measurements of the center-edge angle, acetabular roof angle, and head lateralization index on preoperative and postoperative AP radiographs of the pelvis. Postoperative joint congruency was also evaluated. The cumulative probabilities of radiographic signs of OA progression were estimated with use of the Kaplan-Meier product-limited method and parametric survivorship analysis using the Cox proportional-hazards model was used to determine risk factors for radiographic OA progression.

RESULTS

The mean clinical score improved very slightly, from 15 (SD, 0.8) to 18 (SD, 1.1) (95% confidence interval [CI], -2.9 to -2.0; p < 0.001) in the pre-OA group and from 15 (SD, 1.0) to 16 (SD, 2.1) (95% CI, -2.0 to -1.2; p < 0.001) in the early-stage group at followup. Fourteen patients (15 hips) including one pre-OA patient (one hip) and 13 early-stage patients (14 hips) experienced worsening of their Merle d'Aubigne and Postel score, from a mean of 15 (SD, 0.9) to 12 (SD, 1.6) (95% CI, 1.8-3.3; p < 0.001). Eight patients (nine hips) with early-stage OA preoperatively underwent total hip arthroplasty at a mean duration after rotational acetabular osteotomy of 20 (SD, 2.5) years. Radiographic indices were improved after surgery in both groups. Radiographic progression of OA occurred in 24 patients (25 hips). Kaplan-Meier survivorship analysis, with radiographic signs of progression of OA as the endpoint, predicted survival of 96% (95% CI, 89%-100%) at 10 years and 20 years in the pre-OA group. For the early-stage group, we found survivorship of 89% (95% CI, 83%-95%) at 10 years and 78% (95% CI, 69%-87%) at 20 years. We identified two factors associated with poor outcome: fair (rather than excellent and good) postoperative joint congruency (hazard ratio, 12.1; 95% CI, 3.8-39; p < 0.001) and age older than 46 years at the time of surgery (hazard ratio, 4.6; 95% CI, 1.9-11; p < 0.01).

CONCLUSIONS

Rotational acetabular osteotomy is an effective surgical procedure for symptomatic dysplastic hips in pre- and early-stage OA, and it prevented radiographic OA progression and maintained hip function at a mean 20 years after surgery.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Analysis of contact mechanics in McKee-Farrar metal-on-metal hip implants

Contact mechanics analysis for a typical McKee-Farrar metal-on-metal hip implant was carried out in this study. The finite element method was used to predict the contact area and the contact pressure distribution at the bearing surfaces. The study investigated the effects of the cement and underlying bone, the geometrical parameters such as the radial clearance between the acetabular cup and the femoral head, and the acetabular cup thickness, as well as other geometrical features on the acetabular cup such as lip and studs. For all the cases considered, the predicted contact pressure distribution was found to be significantly different from that based upon the classical Hertz contact theory, with the maximum value being away from the centre of the contact region. The lip on the cup was found to have a negligible effect on the predicted contact pressure distribution. The presence of the studs on the outside of the cup caused a significant increase in the local contact pressure distribution, and a slight decrease in the contact region. Reasonably good agreement of the predicted contact pressure distribution was found between a three-dimensional anatomical model and a simple two-dimensional axisymmetric model. The interfacial boundary condition between the acetabular cup and the underlying cement, modelled as perfectly fixed or perfectly unbonded, had a negligible effect on the predicted contact parameters. For a given radial clearance of 0.079 mm, the decrease in the thickness of the acetabular cup from 4.5 to 1.5 mm resulted in an increase in the contact half angle from 15° to 26°, and a decrease in the maximum contact pressure from 55 to 20 MPa. For a given acetabular cup thickness of 1.5 mm, a decrease in the radial clearance from 0.158 to 0.0395mm led to an increase in the contact half-angle from 20° to 30°, and a decrease in the maximum contact pressure from 30 to 10 MPa. For zero clearance, although the contact pressure was significantly reduced over most of the contact area, the whole acetabular cup came into contact with the femoral head, leading to stress concentration at the edge of the cup. Design optimization of the geometrical parameters, in terms of the acetabular cup thickness and the radial clearance, is important, not only to minimize the contact stress at the bearing surfaces, but also to avoid equatorial and edge contact.

Finite element model of the impaction of a press-fitted acetabular cup

Press-fit surgical procedures aim at providing primary stability to acetabular cup (AC) implants. Impact analysis constitutes a powerful approach to retrieve the AC implant insertion properties. The aim of this numerical study was to investigate the dynamic interaction occurring between the hammer, the ancillary and bone tissue during the impact and to assess the potential of impact analysis to retrieve AC implant insertion conditions. A dynamic two-dimensional axisymmetric model was developed to simulate the impaction of the AC implant into bone tissue assuming friction at the bone-implant interface and large deformations. Different values of interference fit (from 0.5 to 2 mm) and impact velocities (from 1 to 2 m.s^-1) were considered. For each configuration, the variation of the force applied between the hammer and the ancillary was analyzed and an indicator I was determined based on the impact momentum of the signal. The simulated results are compared to the experiments. The value of the polar gap decreases with the impact velocity and increases with the interference fit. The bone-implant contact area was significantly correlated with the resonance frequency (R ² = 0.94) and the indicator (R ² = 0.95). The results show the potential of impact analyses to retrieve the bone-implant contact properties.

A Comparison of the Contact Force Distributions on the Acetabular Surface Due to Orthopedic Treatments for Developmental Hip Dysplasia

We used a three-dimensional rigid body spring model (RBSM) to compare the contact force distributions on the acetabular surface of the infant hip joint that are produced by three orthopedic treatments for developmental dysplasia of the hip (DDH). We analyzed treatments using a Pavlik harness, a generic rigid splint, and a spica cast. The joint geometry was modeled from tomography images of a 1-year-old female. The articular cartilage was modeled as linear springs connecting the surfaces of the acetabulum and the femoral head, whereas the femur and the hip bone were considered as rigid bodies. The hip muscles were modeled as tensile-only preloaded springs. The treatments with the Pavlik harness and the generic rigid splint were modeled for an infant in supine position with a hip flexion angle of 90 deg. Also, since rigid splints are often recommended when children are initiating their gait phase, we modeled the treatment with the infant in standing position. For the spica cast, we only considered the infant in standing position with a flexion angle of 0 deg, and the fixation bar at two heights: at the ankle and at the knee. In order to analyze the effect of the hip abduction angle over the contact force distribution, different abduction angles were used for all the treatments modeled. We have found that the treatments with the infant in supine position, with a flexion angle of 90 deg and abduction angles between 60 deg and 80 deg, produce a more homogenous contact force distribution compared to those obtained for the treatments with the infant in standing position.

Examination Under Anesthesia for Posterior Wall Acetabular Fracture A Survey of the OTA Membership

OBJECTIVES

The purpose of this survey was to learn more about the indications, criteria, and methods surgeons use for performing examination under anesthesia (EUA) for "intermediate" sized posterior wall acetabular fractures (those involving 20% to 40% of the posterior wall) and to find what criteria are used to determine hip instability.

METHODS

An 18 question survey was posted on the Ortho- paedic Trauma Association's website and was used to gather anonymous data from orthopaedic surgeons regarding their approach to the intermediate sized posterior wall fracture.

RESULTS

Considerable variability existed among re- sponses to many of the questions asked. Based on the an - swers given to the survey, a consensus of 75% or more of respondents was found for the following: 1. Supine position for the examination (100%); 2. "Live" fluoroscopy is used during the examination (97%); 3. The AP and obturator oblique are the x-rays most frequently used (81% and 76%, respectively); 4. The hip is placed in flexion and adduction during the exam (100% and 84%, respectively); 5. Axial load is applied during the examination (90%); Finally, 6. instabil - ity is defined as subluxation on exam by most respondents (98%), and any perceived visible subluxation is what defines instability (88%).

CONCLUSION

Most surgeons agreed with the following: 1. Supine is the position of choice for the examination; 2. "Live" fluoroscopy is used during the examination; 3. The AP and obturator oblique are the x-rays most frequently used; 4. The hip is placed in flexion and adduction during the exam; 5. Axial load is applied during the examination; and 6. Instability is defined as subluxation on exam.

What Is the Early/Mid-term Survivorship and Functional Outcome After Bernese Periacetabular Osteotomy in a Pediatric Surgeon Practice?

BACKGROUND

The Bernese periacetabular osteotomy (PAO) is a recognized joint-preserving procedure. Achieving joint stability without creating impingement is important, but the orientation target that best balances these sometimes competing goals has not yet been clearly defined. Moreover, the learning curve of this challenging procedure has not been described.

QUESTIONS/PURPOSES

The purposes of this study were (1) to determine the 10-year survivorship and functional outcome after Bernese PAO in a single-surgeon series; (2) to review which patient, surgical, and radiographic factors might predict outcome after the procedure; and (3) to define the learning curve for target acetabular correction.

METHODS

The first 68 PAOs performed for symptomatic hip dysplasia were retrospectively evaluated. None have been lost to followup with followup less than 2 years. Endpoints for the lost to followup (n = 2) are at the time of when last seen. During the study period, the same surgeon performed 562 pelvic osteotomies (including Salter, Pemberton, Dega and Chiari) and 64 shelf acetabuloplasties. Bernese PAO was used only for symptomatic dysplasia (center-edge angle < 25° and nonhorizontal acetabular roof) in developmentally mature hips without evidence of major joint incongruence or subluxation. Most patients were female (n = 49 [60 hips, 88%]); mean age at operation was 25 years (SD 7). Sixteen hips had previous hip procedures. The study's mean followup was 8 years (range, 2-18 years). Patient-reported functional outcome was obtained using the WOMAC score (best-worst: 0-96). Radiographic parameters of dysplasia (acetabular index [AI], center-edge angle [CEA], congruency, Tönnis grade, and joint space) were evaluated from preoperative and postoperative radiographs using computer software.

RESULTS

The 10-year survival rate was 93% (95% confidence interval [CI], 82%-100%); four patients underwent further surgery to the hip in the study period. The mean WOMAC was 12 (range, 0-54). Factors that influenced survival included joint congruency (100% versus 78%; 95% CI, 61%-96%; p = 0.03) and acetabular orientation correction achieved (AIpostoperative < 15° [100% versus 65%; 95% CI, 43-88; p < 0.001] and CEApostoperative 20° to 40° [100% versus 71.9%; 52.8-100; p < 0.001]). Better WOMAC scores were seen if postoperative AI < 15° (7 versus 25, p = 0.005) and CEA between 20° and 40° (7 versus 23, p = 0.005) were achieved. The chances of obtaining acetabular correction within this range improved after the 20(th) procedure (30% versus 70%, p = 0.008).

CONCLUSIONS

This study reports excellent results after Bernese PAO in the hands of an experienced pediatric hip surgeon. We advocate cautious correction of the acetabular fragment. Future studies should concentrate on how to determine what the optimal target is and how to achieve it intraoperatively, minimizing the learning curve associated with it.

LEVEL OF EVIDENCE

Level III, therapeutic study.

[IMPACT OF SALTER INNOMINATE OSTEOTOMY ON ACETABULAR MORPHOLOGY AND DIRECTION IN DEVELOPMENTAL DISLOCATION OF THE HIP BY THREE-DIMENSIONAL COMPUTER TOMOGRAPHY]

OBJECTIVE

To investigate the impact of the Salter innominate osteotomy on the acetabular morphology and direction and the relationship between them in children with developmental dislocation of the hip (DDH) by three-dimensional CT.

METHODS

Between January 2013 and January 2015, 51 patients with unilateral DDH were treated. All patients were females with an average age of 2 years and 5 months (range, one year and 6 months to 5 years). All the patients underwent open reduction of the hip, Salter innominate osteotomy, proximal femoral osteotomy, and hip cast immobilization for treatment. The data of three-dimensional CT before surgery and at 1 week after surgery were measured and collected as follows: the anterior acetabular index (AAI), posterior acetabular index (PAI), axial acetabular index (AxAI), acetabular anteversion angle (AAA) of the acetabulum, and the distances of the forward, outward, and lateral rotation of the distal osteotomy fragments. The differences of AAI, PAI, AxAI, AAA between before and after surgeries were compared and the difference values of the data with significant difference results were calculated. The relationship between the difference values and the distances of three different rotation directions before and after surgeries were tested by Spearman correlation analysis.

RESULTS

There were significant differences in the AAI, PAI, and AAA between before and after surgery (P < 0.05), but no significant difference was found in the AxAI between before and after surgery (t = 0.878, P = 0.384). The difference values of AAI, PAI, and AAA were (4.518 ± 4.601), (4.219 ± 6.660), and (3.919 ± 4.389)° respectively. The distances of the outward, lateral, and forward rotation of the distal osteotomy fragments after surgery were (0.420 ± 0.339), (2.440 ± 0.230), and (0.421 ± 0.311) cm. There was a significant correlation between the three different rotation directions and AAI difference (P < 0.05), especialy the outward rotation (r=0.981). There was a correlation between the outward, forward rotation and PAI, AAI differences (P < 0.05), and no significant correlation between the lateral rotation and PAI, AAA was found (P > 0.05). There was a significant correlation between the forward rotation and AAA difference (r = 0.841).

CONCLUSION

Salter innominate osteotomy can increase the curvature of the anterior wall of the acetabulum in DDH, but reduce the curvature of the rear wall. At the same time, it can also change the direction of the acetabulum, significantly decrease the acetabular anteversion, but it can not change the depth of the acetabulum. The main factors of the curvature change after Salter innominate osteotomy of DDH is attributable to outward rotation, followed by forward rotation, and the main factor of the acetabular direction change is attributable to forward rotation.

Porous Tantalum Buttress Augments for Severe Acetabular Posterior Column Deficiency

In revision total hip arthroplasty (THA), consensus is lacking regarding the optimal method for reconstruction of the most severe acetabular defects. Porous tantalum (TM) buttress augments were designed for the most severe postero-superior defects. The purpose of this study was to report the results of a consecutive series of acetabular reconstructions utilizing TM buttress augments. Eight complex acetabular reconstructions utilizing a TM buttress augment were performed at two centers. All were Paprosky 3A or Paprosky 3B bone loss classification, with severe superior and posterior column deficiency where wedge augments were insufficient for mechanical support. The acetabular cup sizes ranged from 64-78, and a buttress shim was used in 7 of 8 cases. Clinical and radiographic follow-up averaged 16.5 months (range, 10-28) and no cases were lost to follow-up. There were no cases of clinical or radiographic loosening, and no case had required reoperation or revision. All patients except one were ambulating with either no assist device or a single cane at final follow-up. There was one complication of an iliac wing fracture noted incidentally on postoperative x-rays in the lone patient in whom a buttress shim was not used. At short-term follow-up, TM acetabular buttress augments appear to effectively substitute for the use of structural allografts or cages, which would otherwise be used in this challenging setting. The potential for biologic fixation is promising for the durability of these reconstructions; however, longer-term follow-up is required for full evaluation.

[BIOMECHANICS STUDY ON ACETABULAR POSTERIOR WALL FRACTURE]

OBJECTIVE

To study the experimental biomechanics of acetabular posterior wall fractures so as to provide theoretical basis for its clinical treatment.

METHODS

Six formalin-preserved cadaveric pelvises were divided into groups A and B (n=3). The fracture models of superior-posterior wall and inferior-posterior wall of the acetabulum were created on both hips in group A; fractures were fixed with two interfragmentary screws and a locking reconstruction plate. The fracture models of superior-posterior wall of acetabulum were created on both hips in group B; fractures were fixed with two interfragmentary screws and a locking reconstruction plate at one side, and with acetabular tridimensional memory fixation system (ATMFS) at the other side. The biomechanical testing machine was used to load to 1 500 N at 10 mm/min speed for 30 seconds. The displacement of superior and inferior fracture sites was analyzed with the digital image correlation technology.

RESULTS

No fracture or internal fixation breakage occurred during loading and measuring; the displacement valuess of the upper and lower fracture lines were below 2 mm (the clinically tolerable maximum value) in 2 groups. In group A, the displacement values of the upper and lower fracture lines at superior-posterior wall fracture site were significantly higher than those at inferior-posterior wall fracture site (P < 0.01), and the displacement values of the upper fracture line were significantly higher than those of lower fracture line (P < 0.01) in two fracture types. In group B, the displacement values of the upper and lower fracture lines at the side fixed with screws and a locking reconstruction plate were similar to the values at the side fixed with ATMFS, all being close to 2 mm; the displacement values of the upper fracture line were significantly higher than those of lower fracture line (P < 0.05) in two fixation types.

CONCLUSION

The actual biomechanical effect of the superior-posterior wall of acetabulum is much greater than that of the inferior-posterior wall of acetabulum and they should be discriminated, which might be the reasons of reduction loss, femoral head subluxation, and traumatic arthritis during follow-up.

Fatigue Failure of Newer Generation Modular Revision Femoral Stem Following Fracture Healing: A Case Report

Mechanical failure of the femoral component following total hip arthroplasty is a relatively uncommon complication that has been previously well-described in the literature. Modular, cementless implants have become a popular option in revision total hip arthroplasty. They offer the distinct advantage of optimizing joint kinematics through varying the degree of version, offset, and leg length. We report the case of early fatigue fracture of the Restoration (Stryker, Mahwah, NJ) femoral prosthesis. The following is a detailed description of this case. This report details the events sur - rounding stem failure, and the technique of reconstruction used to deal with this failure.

Femoroacetabular impingement negates the acetabular labral seal during pivoting maneuvers but not gait

BACKGROUND

Experimental disruption of the labrum has been shown to compromise its sealing function and alter cartilage lubrication. However, it is not known whether pathological changes to the labrum secondary to femoroacetabular impingement (FAI) have a similar impact on labral function.

QUESTIONS/PURPOSES

Does damage to the labrum occurring in association with abnormal femoral morphology affect the labral seal?

METHODS

Using 10 fresh cadaveric specimens (mean age 50 years, ±8), we measured the capacity of the central compartment of the hip (the iliofemoral joint) to maintain a seal during fluid infusion, which may help elucidate the function of the labrum during weightbearing. Specimens with and without abnormal femoral morphology (six normal-appearing specimens and four whose geometry suggested cam-type FAI) were tested in postures observed during functional activities, including simulations of normal gait, stooping, and pivoting. Each specimen with FAI morphology exhibited secondary damage of the labrum and the adjacent chondral surface, whereas specimens of normal morphology were undamaged.

RESULTS

Average peak central compartment pressure was reduced during pivoting for specimens with the presence of labral damage secondary to FAI. When placed in pivoting positions, hips with FAI maintained lower fluid pressures within the central compartment compared with intact specimens (15±3 versus 42±8 kPa, respectively; effect size: 1.08 [-0.36 to 2.31]; p=0.007). No differences in peak pressure were observed between groups (FAI versus normal) for postures simulating either gait (21±6 versus 22±4 kPa; p=0.902) or stooping (9±2 versus 8±3 kPa; p=0.775) with the numbers available.

CONCLUSIONS

The acetabular seal, quantified by the maximum intraarticular pressure, was reduced during pivoting; however, the seal was maintained during simulated gait and stooping.

CLINICAL RELEVANCE

Because degeneration is progressive with repetitive impingement, loss of the labral seal starts to be seen during pivoting and may progress from there, but in this small-sample cadaver study that evaluated specimens in middle adulthood, the seal remains intact during simulated gait and stooping. Our study suggests that labral damage secondary to cam-type FAI may reduce the ability of the labral to provide an adequate seal of the central compartment of the hip during loading; however, the extent to which this is affected requires further investigation.

The fate of osteophytes in the superolateral region of the acetabulum after total hip arthroplasty

Acetabular osteophytes are common during total hip arthroplasty (THA). However, the fate and role of superolateral osteophytes of the acetabulum after THA remain unclear. The present study reviewed a series of radiographic changes in the osteophytes on the superolateral region of the acetabulum in 35 hips. The mean follow-up period was 42.2months. The results revealed that the osteophytes that were not in contact with the superolateral edge of acetabular cup were gradually absorbed after THA. In contrast, the osteophytes that were in contact with the superolateral edge of the acetabular cup underwent remodeling, formed regular trabecula, were stress bearing, and eventually integrated with the acetabular cup and the original acetabular bone, and should play a role in stabilizing the acetabular cup.

Does fluoroscopy improve acetabular component placement in total hip arthroplasty?

BACKGROUND

The success of THA largely depends on correct placement of the individual components. Traditionally, these have been placed freehand using anatomic landmarks, but studies have shown poor accuracy with this method.

QUESTIONS/PURPOSES

Specifically, we asked (1) does using fluoroscopy lead to more accurate and greater likelihood of cup placement with the Lewinnek safe zone than does freehand cup placement; (2) is there a learning curve associated with the use of fluoroscopy for cup placement; (3) does the use of fluoroscopy increase operative time; and (4) is there a difference in leg length discrepancy between freehand and fluoroscopic techniques?

METHODS

This series consisted of 109 consecutive patients undergoing primary THA, conversion of a previous hip surgery to THA, and revision THA during a 24-month period. No patients were excluded from analysis during this time. The first 52 patients had cups placed freehand, and then the next 57 patients had acetabular components placed using fluoroscopy; the analysis began with the first patient treated using fluoroscopy, to include our initial experience with the technique. The abduction, version, and limb length discrepancy were measured on 6-week postoperative pelvic radiographs obtained with the patient in the supine position. Operative time, sex, age, BMI, diagnosis, operative side, and femoral head size were recorded as possible confounders.

RESULTS

Cups inserted freehand were placed in the ideal range of abduction (30°-45°) and anteversion (5°-25°) 44% of the time. With fluoroscopy, placement in the Lewinnek safe zone for both measures significantly increased to 65%. The odds of placing the cup in the Lewinnek safe zone for abduction and version were 2.3 times greater with the use of fluoroscopy (95% CI, 1.2-5.0; p = 0.03). Patients undergoing primary THAs (32 freehand, 35 C-arm) had cup placement in the safe zone for abduction and version 44% of the time freehand and 57% of the time with fluoroscopy, which failed to reach statistical significance. There was no difference in operative time, patient age, sex, operative side, diagnosis, limb length discrepancy, or femoral head size between the two groups.

CONCLUSIONS

The use of fluoroscopy to directly observe pelvic position and acetabular component placement increased the success of placement in the Lewinnek safe zone in this cohort of patients having complex and primary THAs. This is a simple, low-cost, and quick method for increasing successful acetabular component alignment. The study population included a large proportion of patients having complex THAs, and further validation of this technique in patients undergoing straightforward, primary THAs needs to be done to understand if similar gains in accuracy for component placement can be expected in that group.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

The effect of 3-column spinal osteotomy on anterior pelvic plane and acetabulum position

Because the spine and pelvis are integrated, changes in spine sagittal balance affect relative acetabulum position. A 1° change of the anterior pelvic plane changes acetabulum anteversion by 0.8°. Three-column spine osteotomies correct fixed sagittal plane deformity. Twenty patients with kyphotic deformity and associated sagittal imbalance underwent corrective 3-column osteotomy. We reviewed upright pelvic and spine radiographs preoperatively and postoperatively and documented the changes in angles. The average sagittal vertical axis was 11.07 cm preoperatively and 4.8 cm postoperatively. Lumbar lordosis changed (on average) from 39° preoperatively to 55° postoperatively (P < .05). Sacral slope increased an average of 6.7° (P = .015). Pelvic tilt decreased by 5.4° (P = .001). The anterior pelvic plane increased by 8.23° (P < .0001). This correction of the sagittal balance is associated with a concomitant increase in sacral slope, pelvic tilt, and the anterior pelvic plane angles. These changes will increase acetabulum anteversion by a predicted 6.54°. This increase will change acetabular cup position and must be considered in patients with spine and pelvic osteoarthritis that requires hip surgery.

Effect of high hip center on stress for dysplastic hip

High hip center reconstruction has been advocated in treating deficient acetabulum. However, there is no consensus on the clinical outcome of this technique. In addition, it remains unclear to what extend this technique restores the normal hip biomechanics. The goal of this study was to investigate stress above the acetabular dome in response to a range of high hip center positioning for Crowe type I and II hip dysplasia. This study consisted of 2 main parts, radiologic and biomechanical. Pelvic radiographs of 18 patients were studied to determine the amount of displacement of the hip center in the superior direction compared with the normal side. Second, qualitative and quantitative changes in stress on cortical and trabecular bone in the region of the acetabular dome as a result of superior displacement of the hip center were analyzed with subject-specific finite element models. The results showed that the range of the hip center position in the superior direction for Crowe type I and II hip dysplasia was 0 to 15 mm above the contralateral femoral head center. When superior displacement of the hip center exceeded 5 mm above the anatomic hip center, cortical bone mass on the 2 thickest cross-sections above the acetabular dome decreased quickly and the stress value on posterolateral cortical bone was obviously lower than the normal level. This study showed that to restore the normal load above the acetabular dome, there is a limit of 5 mm above the anatomic hip center for high hip center acetabular reconstruction for Crowe type I and II hip dysplasia.

Does fluoroscopy with anterior hip arthroplasty decrease acetabular cup variability compared with a nonguided posterior approach?

BACKGROUND

The direct anterior approach for THA offers some advantages, but is associated with a significant learning curve. Some of the technical difficulties can be addressed by the use of intraoperative fluoroscopy which may improve the accuracy of acetabular component placement.

QUESTIONS/PURPOSES

The purposes of this study were to determine if (1) there is decreased variability of acetabular cup inclination and anteversion with the direct anterior approach using fluoroscopic guidance as compared with the posterior approach THA without radiographic guidance; (2) if there is a learning curve associated with achieving accuracy with the direct anterior approach THA. We also wanted (3) to assess the frequency of complications including dislocation with the anterior approach, which initially had a learning curve, and the posterior approach.

METHODS

This retrospective, comparative study of 825 THAs (372 posterior THAs without fluoroscopic guidance and 453 direct anterior THAs, performed by one surgeon, focused on a radiographic analysis to determine cup inclination and anteversion on standardized pelvic radiographs using specialized software. The first 100 direct anterior THAs performed while transitioning from the posterior approach to the direct anterior approach were included in the learning curve group. During this learning curve period, the direct anterior approach was used for all patients except those with conversion of previously fixed intertrochanteric or femoral neck fractures to THAs, gluteus medius tears, and obese patients with an immobile abdominal pannus (100 of 127 THAs). Variability of the acetabular component was compared among the posterior group, learning curve group, and direct anterior group.

RESULTS

Variances for cup inclination and anteversion were significantly lower in the direct anterior group (19 and 16 respectively, p < 0.01) as compared with the posterior group (50 and 79 respectively).Target inclination and anteversion were achieved better in the direct anterior group (98% and 97% respectively) as compared with the posterior group (86% and 77% respectively) (p < 0.01, OR for inclination = 9.1, 95% CI, 3.5 to 23.4; OR for anteversion = 8, 95% CI, 4 to 16). In the learning curve group, target anteversion achieved (91% of cases) was marginally lower than that of the direct anterior group (p = 0.03; OR = 2.9, 95% CI, 1.1 to 7.3) and target inclination (95%) was similar (p = 0.13). There was one posterior dislocation in the posterior group, two anterior dislocations in the learning curve group, and none in the direct anterior group.

CONCLUSIONS

Use of fluoroscopy with the patient in the supine position during direct anterior THA enables intraoperative assessment of cup orientation resulting in decreased variability of acetabular cup anteversion. However, there is a learning curve associated with achieving this accuracy. We could not discern whether this difference was the result of the approach or the use of fluoroscopy in the direct anterior group.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Polyaxial locking and compression screws improve construct stiffness of acetabular cup fixation: a biomechanical study

Bone ingrowth into uncemented acetabular components requires intimate cup-bone contact and rigid fixation, which can be difficult to achieve in revision hip arthroplasty. This study compares polyaxial compression locking screws with non-locked and cancellous screw constructs for acetabular cup fixation. An acetabular cup modified with screw holes to provide both compression and angular stability was implanted into a bone substitute. Coronal lever out, axial torsion and push-out tests were performed with an Instron testing machine, measuring load versus displacement. Polyaxial locking compression screws significantly improved construct stiffness compared with non-locked or cancellous screws. This increased construct stiffness will likely reduce interfacial micromotion. Further research is required to determine whether this will improve bone ingrowth in vivo and reduce cup failure.

New concept in durability improvement of hip total joint endoprostheses

Starting from the well-known fact that the rolling movement always has a lower friction compared to sliding friction, the authors have conceived and realized a pivoting movement joint on a "layer of balls" with "compensation space", placed between the acetabular cup and the femoral head. This technical solution allows free self-directed migration of the balls, depending on the resistance opposed, with successive occupation of the "compensation space". As a concept, the proposed technical solution excludes the existence of a cage for maintaining the relative positions of the spheres. It can be observed that the smallest values of the force and of the friction coefficient are obtained for the prostheses with balls and self-directed movement (approximately 5 times smaller than the values obtained for a classical prosthesis). For all the couples tested, the friction force grows with the growth of the normal load and of the oscillation speed. Changing the contact mechanism for the artificial hip joint from one sliding contact between two large surfaces, to a multitude of rolling contacts, could lead to some problems regarding functionality and durability of the active prosthesis elements. The key to an accurate evaluation of damaging mechanisms acting on THP with self directed rolling balls is a clear and complete picture of the load transfer mechanism.