A new method of measuring acetabular cup anteversion on simulated radiographs

[Feasibility study on measuring anteversion angle of acetabular prosthesis after total hip arthroplasty using arbitrary point method]

Objective

To explore the reliability and accuracy of the arbitrary point method for measuring the anteversion angle of acetabular prosthesis after total hip arthroplasty (THA) based on pelvic X-ray films.

Methods

The clinical data of 23 patients (25 hips) who underwent THA between December 2018 and September 2023 and met the selection criteria were retrospectively analyzed. Among them, there were 16 males and 7 females, with an average age of 57.6 years (range, 34-81 years); 13 hips had THA on the left side and 12 on the right side. There were 19 cases (21 hips) of osteonecrosis of the femoral head, 2 cases (2 hips) of femoral neck fractures, 1 case (1 hip) of developmental dysplasia of the hip, and 1 case (1 hip) of osteoarthritis. After THA, all patients underwent X-ray examination and CT scan. Three physicians measured the anteversion angle of acetabular prosthesis using the arbitrary point method and the CT measurement method respectively, and repeated the measurements three times. The results of the two measurement methods were compared, and the intraclass correlation coefficient (ICC) was employed to assess the reproducibility of the methods.

Results

The anteversion angles of acetabular prosthesis were (15.87±7.73)° measured by the arbitrary point method, and (15.31±7.89)° measured by CT measurement method. There was no significant difference between the two methods ( t=1.515, P=0.143). The ICC of the measurement results by the arbitrary point method for the three physicians were 0.97 ( P<0.001), 0.96 ( P<0.001), and 0.96 ( P<0.001), respectively; and the ICC of the measurement results by CT method were 0.93 ( P<0.001), 0.93 ( P<0.001), and 0.94 ( P<0.001), respectively.

Conclusion

The arbitrary point method for measuring the anteversion angle of acetabular prosthesis after THA based on pelvic X-ray film is easy to operate, accurate, and has high reproducibility.

Radiological assessment of cup anteversion with a novel 3D-printed highly-porous titanium dual mobility cup

BACKGROUND

Cup anteversion after primary total hip arthroplasty (THA) with monobloc dual mobility cups (DMC) is difficult to measure on anterior-posterior (AP) pelvic radiographs because of the implant radiopacity and cup design which do not allow for an accurate visualization of the radiographic projection of the cup equatorial rim and the femoral head. This study aims to radiographically investigate on the reliability and accuracy of different measurement methods for cup anteversion in monobloc DMC THA, by comparing a novel titanium cup with conventional cup designs.

METHODS

97 THAs with a monobloc 3D-printed titanium DMC were radiographically assessed for cup radiographic anteversion (RA) one month postoperatively. RA were measured by three blinded observers through Lewinnek, Woo-Morrey methods and an open access mathematical software (GeoGebra), used as reference method. Intra- and interobserver reliability of RA measurements were evaluated for each method using intraclass correlation coefficient (ICC). Accuracy was assessed comparing Lewinnek and Woo-Morrey methods with GeoGebra. Moreover, further 98 THAs with conventional different brand DMC were radiographically assessed as control group by using the same methods.

RESULTS

ICC for intra- and interobserver reliability for RA measurements with GeoGebra, Lewinnek and Woo-Morrey methods were 0.975-0.980, 0.978 - 0.965, and 0.979 - 0.958, respectively, for the titanium DMC group. Lewinnek resulted more accurate for RA than Woo-Morrey, differing by + 0.4° (p = 0.06) and + 4.4° (p < 0.001) from GeoGebra, respectively. ICC for intra- and interobserver reliability for GeoGebra, Lewinnek and Woo-Morrey methods were 0.848 - 0.756, 0.843 - 0.801, and 0.965 - 0.958, respectively, for the control DMC group. Lewinnek and Woo-Morrey methods differed by -2.3° and + 5.1° from GeoGebra, respectively (p < 0.001).

CONCLUSIONS

RA measurements are more consistent, repeatable and accurate with a titanium DMC than standard DMC, due to the minor radiopacity of the former cup which enable RA measurements on AP radiographs. Conversely, RA measurements of conventional DMC are more consistent but less accurate if performed on cross-table lateral radiographs by Woo-Morrey method than AP radiographs.

The Visual Assessment of Cup Position on Anteroposterior Pelvis Radiographs Before Revision Total Hip Arthroplasty for Instability Is Highly Deceiving

BACKGROUND

Is "eyeballing" enough to determine cup malposition on anteroposterior (AP) pelvis radiographs before revision total hip arthroplasty (rTHA) for instability? We aimed to determine the following: (1) the reliability of eyeballing cup inclination/anteversion on AP pelvis radiographs vs geometrical measurements and (2) whether visual assessments are affected by surgeon experience.

MATERIALS AND METHODS

Fifteen de-identified standing AP pelvis radiographs obtained before rTHA for instability were evaluated by one orthopedic surgeon who measured inclination/anteversion of the cups (n=15) using a new simplified method based on basic geometry. Subsequently, 4 orthopedic surgeons and 4 fellows (postgraduate year 6) assessed inclination/anteversion by eyeballing. A modified Lewinnek safe zone range was employed to categorize each value (in degrees) by geometrical measurements or by raters' eyeballing as within or outside the safe zones. Cohen's kappa (κ) statistics were performed. Mean κ values of attending surgeons and fellows were compared.

RESULTS

According to geometrical measurements, 8 and 12 cups were in malposition (for inclination and anteversion, respectively). By just eyeballing, no attending surgeon or fellow attained an excellent (κ>0.8) level of agreement when compared with geometrical measurements. Only 1 attending surgeon attained a substantial (κ=0.6-0.8) level of agreement (κ=0.737, for inclination, P=.003). Mean κ values of attending surgeons and fellows were 0.476 and 0.187, respectively, for inclination (P=.2) and 0.416 and 0.428, respectively, for anteversion (P=.9).

CONCLUSION

Eyeballing cup position on AP pelvis radiographs before rTHA for instability is extremely misleading, regardless of surgeon experience. It is imperative to always measure the inclination and anteversion of the cup. [Orthopedics. 2025;48(1):e22-e26.].

A novel method of acetabular component anteversion measurement on plain radiographs

BACKGROUND

Acetabular component anteversion (ACA) markedly impacts the outcome of total hip arthroplasty (THA) and thus is routinely measured on radiographs postoperatively. However, clinical ACA measurement methods are either too complicated or subjective due to three drawbacks: complex calculations, measurement of obscured points, and complex geometric drawings. This study aimed to develop a precise and convenient novel method of measuring ACA on routine radiographs without the three drawbacks and to verify its accuracy and reliability by comparing it against existing methods.

METHODS

A novel geometric principle to measure ACA was developed. Accordingly, a protractor was designed to measure radiographic anteversion (RA) on anteroposterior (AP) hip radiographs. Three researchers measured RA twice, using the protractor, McLaren's, and Pradhan's method on 26 computer-simulated radiographs with pre-set RAs and 20 actual radiographs. Accuracy was assessed by errors on simulated radiographs, and reliability was assessed by results of measurements on simulated and actual radiographs.

RESULTS

The absolute error of the novel method (1.01° ± 1.06°) was lower than McLaren's method (1.34° ± 1.16°) (p < 0.05) and not significantly different from Pradhan's method (1.10° ± 1.02°) (p = 0.392). The protractor's intra-rater and inter-rater reliability were good-to-excellent or excellent and higher or equivalent to the two other methods.

CONCLUSIONS

The novel method avoids the three major drawbacks of conventional methods. Its accuracy is significantly higher than McLaren's method and comparable to Pradhan's. The novel method has higher or non-inferior accuracy and reliability than McLaren's and Pradhan's methods.

Body morphometry did not affect the accuracy of a second-generation, miniature imageless navigation system for total hip arthroplasty (THA) using a posterior approach

Introduction

Some modern imageless navigation platforms for total hip arthroplasty (THA) rely on virtual frontal and sagittal planes determined with the patient in the lateral decubitus position. Body morphometry that changes with gender, body mass index, and other demographic factors may affect accuracy in patient positioning and consequently, navigation accuracy. The objective of this study was to analyze the influence of patient factors on the intraoperative accuracy of a second-generation imageless computer-assisted surgery platform.

Methods

325 consecutive patients undergoing posterior approach, navigated THA arthroplasty for primary osteoarthritis by a single surgeon were retrospectively reviewed. An optic-based imageless navigation system referenced off a generic sagittal and coronal plane was used to determine acetabular inclination and anteversion. Acetabular accuracy was determined by assessing differences between intraoperative values and those obtained from measuring standardized 6-week follow-up radiographs. The effect of age, gender, BMI, race, ethnicity, and laterality on acetabular accuracy was assessed via t-tests, Pearson correlation and ANOVA.

Results

Gender had a significant impact on raw inclination accuracy (females and males had an average error of 1.41° and -1.03°, respectively - p < 0.001). There was a weak correlation between acetabular accuracy and patient age and BMI as a continuous variable (both absolute γ < 0.2). No difference was found between acetabular accuracy and BMI groups.

Conclusion

This second-generation imageless computer assisted device provided accurate cup positioning regardless of patient's BMI. Gender was the only factor impacting inclination accuracy.

Defining the Learning Period of a Novel Imageless Navigation System for Posterior Approach Total Hip Arthroplasty: Analysis of Surgical Time and Accuracy

Introduction

The use of imageless navigation in total hip arthroplasty (THA) is frequently associated with prolonged surgical times, predominantly during the learning period. The purpose of the present study was to characterize the learning period of a novel imageless navigation system, specifically as it related to surgical time and acetabular navigation accuracy.

Materials and Methods

This was a retrospective observational study of a consecutive group of 158 patients who underwent primary unilateral THA for osteoarthritis by a team headed by a single surgeon. All procedures used an imageless navigation system to measure acetabular cup inclination and anteversion angles, referencing a generic sagittal and frontal plane. Navigation accuracy was determined by assessing differences between intraoperative inclination and anteversion values and those obtained from standardized 6-week follow-up radiographs. Operative time and navigation accuracy were assessed by plotting moving averages of 7 consecutive cases. The learning period was defined using Mann-Kendall trend analyses, student t-tests and nonlinear regression modeling based on surgical time and navigation accuracy. Alpha error was 0.05.

Results

The average surgical time was 67.3 min (SD:9.2) (range 45-95). The average navigation accuracy for inclination was 0.01° (SD:4.2) (range - 10 to 10), and that for anteversion was - 4.9° (SD:3.8) (range - 14 to 5). Average surgical time and navigation accuracy were similar between the first and final cases in the series with no learning period detected.

Conclusions

There was no discernible learning period effect on surgical time or system measurement accuracy during the early phases of adoption for this imageless navigation system.

Standardized 3D-printed trabecular titanium augment and cup for acetabular bone defects in revision hip arthroplasty: a mid-term follow-up study

BACKGROUND

The aim of this study was to assess the feasibility and outcomes of standardized three-dimensional (3D)-printed trabecular titanium (TT) cups and augments to reconstruct most acetabular defects.

METHODS

We included 58 patients with Paprosky type II and III acetabular bone defects who underwent revision hip arthroplasty between 2015 and 2018. Patients who were revised without 3D-printed augments, and cases who were lost to follow-up and died during follow-up were excluded. Radiographic and clinical outcomes were evaluated. A Kaplan-Meier survivorship curve was generated. The mean follow-up was 64.5 (range 49-84) months.

RESULTS

In total, 48 (82.8%) acetabular revisions were performed using standardized 3D-printed TT cups and augments, and a retrospective review was conducted on 43 revisions. The average position of the vertical center of rotation and leg length discrepancy were significantly decreased from 42.4 ± 9.1 mm and 38.4 ± 10.7 mm to 22.8 ± 3.4 mm and 4.1 ± 3.0 mm, respectively. Non-progressive radiolucent lines were observed in 3 (7.5%) acetabular components with no indications for revision. The mean Harris hip score, Oxford hip score and EuroQol five-dimensional questionnaire score increased from 33.0 ± 10.7, 11.4 ± 3.4 and 0.29 ± 0.09 to 80.3 ± 8.8, 35.8 ± 2.4 and 0.71 ± 0.10, respectively. The revision-free survival rate of the acetabular component was 93.0% (40/43), with a rate of revision for aseptic loosening of 2.3% (1/43).

CONCLUSION

Standardized 3D‑printed TT augments and cups could be used to reconstruct the majority of Paprosky type II and III acetabular defects in revision hip arthroplasty and demonstrated encouraging results at mid-term follow-up.

Use of a novel imageless navigation system reduced fluoroscopy exposure and improved acetabular positioning in anterior approach total hip arthroplasty: a case-control study

INTRODUCTION

Direct anterior approach (DAA) for total hip arthroplasty (THA) frequently utilizes fluoroscopy. The purpose of this study is to assess the impact of using a novel, imageless THA navigation system on radiation exposure and acetabular cup placement consistency.

MATERIALS AND METHODS

This was a retrospective, single-surgeon cohort study of a consecutive group of patients who underwent DAA THA for osteoarthritis. An optic-based imageless navigation system was used to determine intraoperative acetabular inclination and anteversion angles referenced off of a generic coronal and sagittal plane in 71 cases (study group). These were compared with 71 manual cases (control group) for fluoroscopy exposure, operative duration, and acetabular placement variation. Cohorts were similar in their distributions of sex, race, ethnicity, and body mass index. Comparisons between groups were made using independent samples t tests. Alpha error was 0.05.

RESULTS

Study patients experienced significantly less fluoroscopy exposure time {3.59 [Standard Deviation (SD) 1.95] vs. 9.15 (SD 5.98) seconds; p < 0.001} and dosage (0.30 [SD 0.23] vs. 0.78 [SD 0.63] mGy; p < 0.001). Study and control patients had similar operative times [82.69 (SD 11.70) vs. 89.54 (SD 14.60) minutes; p = 0.09]. The study group had a significantly lower radiographic variation for inclination and anteversion, based on mean proximity to the centroid of each cohort [3.55 (SD 1.88) vs. 5.39 (SD 3.51); p < 0.001] and also a greater proportion of cases that fell within 1 SD of the mean cohort inclination and anteversion (40.8% vs. 21.1%; p = 0.009).

CONCLUSIONS

Use of a novel imageless navigation system for DAA THA significantly reduced fluoroscopic radiation exposure and improved consistency in acetabular cup placement.

Comparison of the early clinical efficacy of the SuperPath approach versus the modified Hardinge approach in total hip arthroplasty for femoral neck fractures in elderly patients: a randomized controlled trial

PURPOSE

To investigate the clinical efficacy and advantages of the SuperPath approach for total hip arthroplasty in the treatment of femoral neck fractures in the elderly population.

METHODS

From February 2018 to March 2019, 120 patients were randomly divided into two groups with 60 patients each: the SuperPath group and the conventional group. The results evaluated included the general operation situation, serum markers, blood loss, pain score, hip function and prosthesis location analysis.

RESULTS

There was no demographic difference between the two groups. Compared with the conventional group, the SuperPath group had a shorter operation time (78.4 vs. 93.0 min, p = 0.000), a smaller incision length (5.8 vs. 12.5 cm, p = 0.000), less intraoperative blood loss (121.5 vs. 178.8 ml, p = 0.000), a shorter hospitalization time (8.0 vs. 10.8 days, p = 0.000) and less drainage volume (77.8 vs. 141.2 ml, p = 0.000). The creatine kinase level in the SuperPath group was significantly lower than that in the conventional group, while there was no difference in the C-reactive protein level and erythrocyte sedimentation rate level. The visual analog scale score was lower one month postoperatively, and the Harris hip score was higher three months postoperatively in the SuperPath group (p < 0.05). There was no difference in the cup abduction angle or anteversion angle of the two groups.

CONCLUSION

We found better clinical efficacy after using the SuperPath approach with less muscle damage, less postoperative pain and better postoperative function than after using the modified Hardinge approach. Trial registration The randomized clinical trial was retrospectively registered at the Chinese Clinical Trial Registry on 31/12/2020 (ChiCTR-2000041583, http://www.chictr.org.cn/showproj.aspx?proj=57008 ).

Lumbar spinal fusion does not increase early dislocation risk in primary total hip arthroplasty through the direct anterior approach

INTRODUCTION

Patients with total hip arthroplasty (THA) and a concomitant lumbar spinal fusion (LSF) might have an increased incidence of revision surgery and postoperative complications such as early THA dislocation. The direct anterior approach (DAA) has gained popularity in THA due to its soft tissue-preserving nature and the relatively low dislocation risk. The purpose of the present study was to examine whether LSF patients undergoing minimally invasive THA through the DAA might have an increased risk of prosthetic-related complications compared to matched-control patients without a LSF.

MATERIALS AND METHODS

Patients who underwent THA through the DAA in our institution from January 2014 to December 2018 were identified. A total of 30 primary THA also underwent LSF within 3 months from the initial operation. These patients were randomly matched (1:3) for sex, age, and body mass index with patients who underwent primary THA in our institution without a history of LSF (control group). Peri and postoperative complications, revisions, radiographic and clinical outcomes were assessed retrospectively.

RESULTS

LSF patients who underwent THA through the DAA did not have an increased risk of prosthetic-related complications compared to matched-control subjects without a LSF (6.6% versus 4.4%, P < 0.05). The functional and radiological outcomes were similar between groups.

CONCLUSION

LSF patients undergoing THA could benefit from the DAA similarly to patients without LSF and without increased rate of early THA dislocation. Although the complex interplay between the lumbar spine and hip in THA patients warrants further investigation, the outcomes of THA through the DAA in LSF patients appear promising.

LEVEL OF EVIDENCE

Retrospective case-control study, III.

Constrained acetabular liners are a viable option in second-stage re-implantation for chronic infected total hip arthroplasty with abductor or greater trochanter deficiency and large acetabular bone defects

Background

Abductor mechanism deficiency is a clear indication for using constrained acetabular liners (CALs), and large acetabular bone defects are considered a relative contraindication to CALs. We report the results of using CALs in special cases in which abductor or greater trochanter deficiency was accompanied by large acetabular bone defects at second-stage re-implantation for chronic infected total hip arthroplasty (THA).

Methods

Between January 2010 and January 2018, 19 patients who used CALs at second-stage re-implantation and had abductor or greater trochanter deficiency and large acetabular bone defects were included in this study. We followed up with the clinical and radiological results of these patients. Complications and infection-related information were also recorded.

Results

Eight patients, 4 patients, and 7 patients had Paprosky type IIB, type IIC, and type IIIA acetabular bone defects at second-stage re-implantation, respectively. The indication for using CALs was abductor deficiency in 14 patients and greater trochanter deficiency in the other 5 patients. The mean follow-up was 74.4 months (range 50–96). The mean Harris Hip Score (HHS) was 76.3 points (range 62–86) at the last follow-up. Three patients presented acetabular radiolucent lines with no progress: zone 3, zone 3 and zone 2 and 3, respectively. One patient suffered transient sciatic nerve palsy. There was no dislocation, failure of the CALs, reoperation, or recurrence of infection.

Conclusion

Our results suggested that for screened patients, CALs are a viable option in second-stage re-implantation for chronic infected THA with abductor or greater trochanter deficiency and large bone defects.

Ceramic-on-ceramic versus ceramic-on-polyethylene in total hip arthroplasty: a comparative study at a minimum of 13 years follow-up

BACKGROUND

Nowadays hip replacement is one of the most successful surgery in terms of clinical outcome and patient's satisfaction. Therefore, the choice of biomaterials in hip replacement is increasingly important with the aim of obtaining a long-term satisfaction of patient and a greater survivorship of the implants. Ceramic-on-polyethylene (COP) and ceramic-on-ceramic (CoC) bearings are two common coupling used in total hip arthroplasty. The aim of this retrospective study was to compare clinical and radiological outcomes between patients treated using CoC and CoP THA at a mean follow-up of 15 years.

METHODS

86 patients, average age 65.6, were included in the study: 43 in group A bearing CoC and 43 in group B bearing CoP. Minimum follow-up was 13 years. Primary outcome was a clinical evaluation assessed by HOOS and SF-12 questionnaires. Secondary outcome was a radiological evaluation on a A-P pelvis x-ray calculating acetabular cup inclination and anteversion and detecting osteolysis.

RESULT

After a multivariate analysis was performed, our results show clinical outcomes in group B significantly better than in group A: statistically significant value (p < 0,05) was found in the mean HOOS-symptoms subscale (83.0 ± 15.4 in Group A vs 90.3 ± 12.2 in group B) in the SF-12 physical component score (39.7 ± 11.0 in Group A vs 48.1 ± 10.1 in group B) and in HOOS (79.0 ± 16 in Group A vs 87.0 ± 16 in group B). 3 squeaking was found in group A. The calculated mean acetabular cup inclination value was 44,87 in group A and 44,5 in group B and the mean socket version was 17,54 in group A and 15,10 in group B. No significant statistically relationship between radiographic parameters analyzed and clinical outcomes was noted.

CONCLUSION

The current results provide us important information about the THA long-term outcome. CoP offered significantly better results compared with CoC at long-term follow up, and thus it should be considered in the choose of bearing in THA.

Clinical and radiographic outcomes after total hip arthroplasty with the NANOS neck preserving hip stem: a 10 to 16-year follow-up study

BACKGROUND

Short-stem Hip Arthroplasty (SHA) are increasingly implanted in recent years thanks to their potential advantage in preserving metaphyseal bone-stock. Among them, the NANOS® short-stem implant demonstrated satisfactory results to short and mid-term. The purpose of this retrospective study was to evaluate the clinical and radiographic outcome of the Nanos® short stem at a minimum follow-up of 10 years.

METHODS

Sixty-seven patients aged 53 ± 20 years were enlisted in the study, for a total of 72 hips. Primary outcomes were survivorship of the implant and clinical outcome measured using the Hip disability and Osteoarthritis Outcome scores (HOOS) and the Short Form Survey (SF12) questionnaire. The secondary outcome was a radiological evaluation calculating the inclination and the anteversion angle of the acetabular cup for each implant and investigating osteolysis, heterotopic ossifications and stem position.

RESULTS

We observed a 95.5% stem survivorship. The complication rate was 7.6% and three implants underwent revision because of an aseptic loosening, an infection and a periprosthetic fracture due to trauma. Among 58 patients (63 hips) evaluated in an outpatient visit 10-16 years after surgery, improvement in clinically relevant scores comparing with baseline was observed: HOOS score increased after surgery in all its subcategories (from 32.25 ± 14.07% up to 91.91 ± 9.13%) as well as SF12 which increased by more than 18 percentage points. On clinical assessment, the range of motion (ROM) was restored at follow-up, 1 patient (1.7%) showed a squeaking hip and 2 (3.4%) reported leg-length discrepancy. Neutral stem positioning was achieved in 58 hips and heterotopic ossifications occurred in 10 hips (16%).

CONCLUSIONS

The current study reports good clinical and radiological outcomes following NANOS® short-stem hip implant at minimum 10 years-follow-up. Since the high rate of stem survivorship, the low complication rate demonstrated and the overall patient satisfaction, our results suggest NANOS® neck-preserving prostheses should be considered as a valid alternative to standard implants.

Identification of risk factors for treatment failure of closed reduction and abduction bracing after first-time total hip arthroplasty dislocation

INTRODUCTION

After a first-time total hip arthroplasty (THA) dislocation, a closed reduction followed by partial immobilization in an abduction brace is the recommended therapy. Despite modern abduction braces the success rate of conservative therapy is limited and evidence is scarce. The aim of this study was to identify risk factors for failure of conservative treatment after THA dislocation.

MATERIAL AND METHODS

Eighty-seven patients, with conservative treatment of a first-time dislocation of a primary or revision THA, were included in this retrospective cohort study. Success was defined as a stable THA for a minimum of 6 months. Re-dislocation, open reduction or revision was defined as failure. The following risk factors were analyzed: gender, age, body mass index (BMI), ASA (American Society of Anesthesiologists) score, time of dislocation, head size, cup orientation, leg length, center of rotation and offset.

RESULTS

Sixty-seven percent of all patients experienced a re-dislocation, despite standardized conservative therapy. A BMI ≥ 25 kg/m², early THA dislocation, and low cup anteversion were associated with a statistically significantly higher risk for re-dislocation. None of the other risk-factors achieved statistical significance. A multifactorial risk-factor analysis was performed to assess whether a cup position outside of Lewinnek's safe zone in combination with gender, BMI and time to dislocation showed statistical significance for re-dislocation. Both BMI ≥ 25 kg/m² and early dislocation showed a statistically higher failure rate. Cup position and gender were not significant.

CONCLUSIONS

BMI ≥ 25 kg/m², early THA dislocation and low cup anteversion were identified as significant risk factors for failure of conservative treatment with an abduction brace for first-time THA dislocation.

Total Hip Arthroplasty Performed with a Novel Design Type 1 Femoral Stem: A Retrospective Minimum 5-Year Follow-up Study

Background

The Bencox M stem is a mid-short type 1 stem with additional unique design features. It has a reduced stem length and a lateral shoulder to facilitate minimally invasive surgery, as well as an angular lateral shoulder and a trapezoidal neck to minimize stem-liner impingement. There have been many mid-term reports on type 1 stems, but no results have been reported so far on this novel design type 1 femoral stem. This study presents the clinical and radiological outcomes of total hip arthroplasty performed with the M stem after a minimum 5-year follow-up.

Methods

From July 2014 to February 2015, 125 primary total hip arthroplasties using the M cementless femoral stem were performed on 112 patients in our hospital. Among them, 94 patients (106 hips) were eligible for the study and were followed up for more than 5 years. Our primary outcome was clinical results, which were evaluated by the Harris Hip Score (HHS), thigh pain, noise, and other complications. Secondary outcome was radiological outcomes. Seventy-seven hips were evaluated radiologically with attention to implant fixation, migration, loosening of component, degree of stress shielding, radiolucent lines, focal osteolysis, heterotopic ossification, and the evidence of impingement between the stem and liner.

Results

The average HHS improved from 54.6 points (range, 24–67 points) to 96.8 points (range, 91–100 points) at the latest follow-up. Three hips (2.8%) had intermittent thigh pain, which was tolerable without medication. Five hips (4.7%) had ceramic-related noise. There were no other complications such as infection, nerve injury, dislocation, or revision. All implants showed radiographic evidence of stable fixation by bone ingrowth without migration. Fifty-seven hips (74%) showed mild femoral stress shielding. Distal cortical hypertrophy was detected in 7 hips (9%), and heterotopic ossification was observed in 17 hips (22%). No implant demonstrated focal osteolysis and notching of the femoral neck or shoulder on radiographs.

Conclusions

The minimum 5-year results of total hip arthroplasty performed with the M cementless femoral stem were encouraging clinically and radiologically. A long-term follow-up will be necessary to evaluate its longevity.

Lumbar Spine Fusion and Symptoms of Leg Length Discrepancy After Hip Arthroplasty

BACKGROUND

Hip length discrepancy (HLD) is common after total hip arthroplasty (THA); however, the effect of spinal fusion on perceived leg length discrepancy (LLD) symptoms after THA has not been examined. This study tested the hypothesis that LLD symptoms are increased in patients who underwent lumbar spinal fusion and THA, compared with patients with THA only.

METHODS

This retrospective cohort study included 67 patients who underwent lumbar spinal fusion and THA, along with 78 matched control patients who underwent THA only. Hip and spine measurements were taken on postoperative, standing anterior-posterior pelvic, lateral lumbar, and anterior-posterior lumbar spinal radiographs. Perceived LLD symptoms were assessed via telephone survey.

RESULTS

Between the spinal fusion and control groups, there was no significant difference in HLD (M = 7.10 mm, SE = 0.70 and M = 5.60 mm, SE = 0.49) (P = .403). The spinal fusion patients reported more frequently noticing a difference in the length of their legs than the control group (P = .046) and reported limping "all the time" compared with the control group (P = .001). Among all patients with an HLD ≤10 mm, those in the spinal fusion group reported limping at a higher frequency than patients in the control group (P = .008). Patients in the spinal fusion group were also more likely to report worsened back pain after THA (P = .011) than the control group.

CONCLUSION

Frequencies of a perceived LLD, limping, and worsened back pain after THA were increased in patients with THA and a spinal fusion compared with patients who had THA only, even in a population with HLD traditionally considered to be subclinical. The results indicate that in patients with prior spinal fusion, precautions should be taken to avoid even minor LLD in the setting of THA.

Dislocation rates following total hip arthroplasty via the direct anterior approach in a consecutive, non-selective cohort

AIMS

Use of the direct anterior approach (DAA) for total hip arthroplasty (THA) has increased in recent years due to proposed benefits, including a lower risk of dislocation and improved early functional recovery. This study investigates the dislocation rate in a non-selective, consecutive cohort undergoing THA via the DAA without any exclusion or bias in patient selection based on habitus, deformity, age, sex, or fixation method.

METHODS

We retrospectively reviewed all patients undergoing THA via the DAA between 2011 and 2017 at our institution. Primary outcome was dislocation at minimum two-year follow-up. Patients were stratified by demographic details and risk factors for dislocation, and an in-depth analysis of dislocations was performed.

RESULTS

A total of 2,831 hips in 2,205 patients were included. Mean age was 64.9 years (24 to 96), mean BMI was 29.2 kg/m² (15.1 to 53.8), and 1,595 patients (56.3%) were female. There were 11 dislocations within one year (0.38%) and 13 total dislocations at terminal follow-up (0.46%). Five dislocations required revision. The dislocation rate for surgeons who had completed their learning curve was 0.15% compared to 1.14% in those who had not. The cumulative periprosthetic infection and fracture rates were 0.53% and 0.67%, respectively.

CONCLUSION

In a non-selective, consecutive cohort of patients undergoing THA via the DAA, the risk of dislocation is low, even among patients with risk factors for instability. Our data further suggest that the DAA can be safely used in all hip arthroplasty patients without an increased risk of wound complications, fracture, infection, or revision. The inclusion of seven surgeons increases the generalizability of these results. Cite this article: Bone Joint J 2021;103-B(7 Supple B):38-45.

Primary Total Hip Arthroplasty in Patients With Ankylosing Spondylitis

BACKGROUND

Ankylosing spondylitis (AS) is a common inflammatory spondyloarthropathy with hip involvement in 40% of patients. With the renewed interest in the hip-spine interplay, this study aimed to define long-term outcomes of primary total hip arthroplasty (THA) in the setting of AS.

METHODS

We identified 309 hips (219 patients) with AS treated with primary THA from 1969 to 2018. Mean age was 49 years, 80% were males, and mean body mass index was 28 kg/m². Cumulative incidences of any revision, reoperation, and dislocation were calculated utilizing a competing risk analysis. Harris Hip Scores and complications were also reported. Mean follow-up was 16 years.

RESULTS

The cumulative incidence of any revision after primary THA was 2.3% at 5 years and 17.5% at 20 years. The most common reasons for revision (n = 73) were aseptic loosening (41%), osteolysis/polyethylene (PE) wear (30%, all with conventional PE), and femoral component fracture (8%). The cumulative incidence of dislocation was 1.9% at 5 years and 2.9% at 20 years. Younger age was associated with increased risk of revision (hazard ratio (HR) = 1.3, P < .01) and reoperation (HR = 1.2, P < .01), but not dislocation (HR = 0.7, P = .1). Twenty-eight hips (9%) experienced a postoperative complication not requiring reoperation. The mean Harris Hip Score improved from 51 to 76 after THA (P < .001).

CONCLUSION

In this series of 309 primary THAs in patients with AS, the 20-year cumulative incidence of any revision after primary THA was 17.5%. Aseptic loosening, osteolysis/PE wear, and femoral component fracture were the most common reasons for revision. Notably, the cumulative incidence of dislocation at 20 years was only 2.9%.

LEVEL OF EVIDENCE

Level IV.

Impingement Between the Metal Stem and the Ceramic Liner in Total Hip Arthroplasty: The Neck Is Not the Only Place Where Impingement Occurs

BACKGROUND

It is assumed that impingement between the ceramic liner and the stem increases the possibility of a liner fracture in total hip arthroplasty with a ceramic-on-ceramic bearing. The purpose of this study was to analyze the pattern of the impingement by evaluating the notches (U-shaped indented wear scars engraved on the stem) on radiographs to determine when and where impingement develops and to analyze the factors affecting its occurrence.

METHODS

Among the primary total hip arthroplasty cases using a ceramic-on-ceramic bearing performed from November 1997 to December 2003, 244 cases of 197 patients (123 male patients and 74 female patients) that had follow-up of ≥15 years were included. All of the radiographs were examined with special regard to the notches and the cup positions.

RESULTS

Notches were detected at 77 sites of 57 cases (23.4%) for the first time between 8 months and 14.8 years after the surgical procedure. They were located on the neck or the shoulder of the stem. Shoulder notches were detected only in the cases with a short-neck head. Shoulder notches were found in 29 cases (20.0% of short-neck cases). Cup inclination was lower (p = 0.01) and anteversion was higher (p = 0.01) in the group with notches than the group without notches. There were 5 cases of ceramic head fracture. One of them experienced another ceramic liner fracture, assumed to be caused by prosthetic shoulder impingement, after the revision surgical procedure.

CONCLUSIONS

The results of this study suggest that impingement between the stem and the ceramic liner occurs in a considerable proportion of patients who underwent total hip arthroplasty not only on the neck but also on the shoulder of the stem. Forceful and abrupt impingement on the stem shoulder can cause ceramic liner fracture. Impingement between the stem shoulder and the ceramic liner should be considered in designing a stem. It seems to be prudent to recommend that patients avoid squatting or sitting cross-legged on the floor as much as possible.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Intra-operative referencing technique is non-inferior to use of fluoroscopy for acetabular component positioning in anterior hip arthroplasty

BACKGROUND

Intra-operative fluoroscopy has been shown to improve the accuracy of acetabular component positioning when compared to no fluoroscopy in direct anterior approach (DAA) total hip arthroplasty (THA). Due to logistical reasons, our senior author has been performing DAA THA at one institution without the use of fluoroscopy and has created an intraoperative referencing technique to aid in acetabular component positioning. The purpose of this study is to evaluate the accuracy of acetabular component positioning using fluoroscopy when compared to an intra-operative referencing technique without fluoroscopy.

METHODS

A total of 214 consecutive primary DAA THA were performed by one surgeon at two institutions and were retrospectively reviewed over a 3-year period. Intra-operative fluoroscopy was used with all patients at Institution A (N = 154). At institution B (N = 60), no fluoroscopy was used, and an intra-operative referencing technique was employed to assist in placement of the acetabular component.

RESULTS

In the fluoroscopy group, 91% of components met our abduction target, 90% met our anteversion target, and 82.5% simultaneously met both targets. In the non-fluoroscopy group, 98% of components met our abduction target, 92% met our anteversion target, and 90% simultaneously met both targets. There was no difference between groups for placement of the component within both targets simultaneously (p = .171).

CONCLUSION

Use of our intra-operative referencing technique is non-inferior in placing acetabular components within a pre-defined safe zone when compared to use of intraoperative fluoroscopy. The intra-operative reference technique can be a helpful adjunct for ensuring accurate acetabular component positioning while simultaneously reducing cost and limiting radiation exposure.

Ceramic Liner Fracture Caused by an Impingement between the Stem Shoulder and the Ceramic Liner

Mechanisms of ceramic liner fractures have not yet been fully elucidated. Impingement between a stem and ceramic liner is a proposed cause of ceramic liner fractures. We experienced a case of ceramic liner fracture caused by direct impingement between the stem shoulder and the ceramic liner. This type of impingement, unlike impingements with a stem neck, has not been previously reported. While we assume that certain characteristics of the stem contributed to the impingement, we report this case to note that caution may be needed when using certain stem designs.

Dual-Mobility Constructs in Primary Total Hip Arthroplasty in High-Risk Patients With Spinal Fusions: Our Institutional Experience

Background

Prior spinal fusion significantly increases the risk of dislocation in patients after total hip arthroplasty (THA). Owing to these high risks, surgeons may use dual-mobility (DM) constructs in these patients to optimize hip stability. However, there is a paucity of data on the outcomes of DM constructs in patients who underwent prior spinal fusions.

Methods

We retrospectively identified 80 patients (86 THAs) who underwent a spinal arthrodesis and a subsequent posterior approach THA with a DM construct. The median number of levels fused was 4, with 59 (74%) patients having 2 or more levels fused; in addition, 50 (63%) patients were fused to the sacrum. Ninety percent and 55% of THAs were within the Lewinnek safe zone for inclination and anteversion, respectively. Patients were evaluated for any episode of hip instability, complications, and patient reported outcome measures.

Results

At 3-year mean follow-up, no patients sustained a postoperative dislocation or intraprosthetic dislocation (0%). Overall, there were 6 (7.5%) complications during the study period leading to reoperation in 3 (4%) patients, none related to the acetabular component or instability. Hip Injury and Osteoarthritis Outcome Score, Joint Replacement scores significantly improved from a mean of 50 preoperatively to 87 postoperatively (P < .001), and the Veterans Rand 12 Item Health Survey physical score improved from a mean of 31 preoperatively to 44 postoperatively (P < .001).

Conclusion

In a high-risk series of patients who underwent prior spinal fusion, posterolateral primary THA with a DM construct demonstrated no dislocations at mean 3-year follow-up. Although these early data are clearly encouraging, more patients with longer term follow-up are needed.

Intermediate to Long-Term Follow-up of Cementing Liners into Well-Fixed Acetabular Components

BACKGROUND

The cementation of a new liner into a well-fixed acetabular component is common during revision total hip arthroplasty (THA) for many indications, but most commonly for lack of a modern, compatible, highly cross-linked polyethylene (HXLPE) liner. However, little is known about the intermediate-term to long-term durability of this strategy. The purpose of this study was to evaluate the implant survivorship, risk of complications, clinical outcomes, and radiographic results of cementing a new HXLPE liner into a well-fixed acetabular component.

METHODS

We retrospectively identified 323 revision THAs in which a nonconstrained HXLPE liner was cemented into a well-fixed acetabular component. The mean age at the time of the revision THA was 63 years, and 50% of patients were female. The most common indications for revision THA were polyethylene wear and osteolysis (48%), aseptic femoral loosening (35%), and hip instability (8%). The mean follow-up was 9 years.

RESULTS

Polyethylene liner failure occurred in 11 cases (3%). In all cases, the cemented liner dissociated from the acetabular component. At 10 years, the survivorship free from any revision was 80% (95% confidence interval [CI], 75% to 84%) and the survivorship free from any reoperation was 77% (95% CI, 72% to 82%). The most common reason for re-revision was dislocation (45% of reoperations). A dislocation occurred in 17% of cases. Hips that underwent revision for instability were significantly more likely to dislocate compared with hips that underwent revision for liner wear (hazard ratio [HR], 2.3 [95% CI, 1.2 to 4.5]; p = 0.02). Elevated rim or face-changing liners were significantly more likely to dissociate than flat liners (HR, 9.0 [95% CI, 1.2 to 70.6]; p = 0.04).

CONCLUSIONS

Cementation of a nonconstrained HXLPE liner into a well-fixed acetabular component during revision THA provided durable fixation with only a small number of failures at the cement interface (3%). Instability after this procedure remains a concern, but this is multifactorial in nature. These data support the continued use of this technique, when necessary, during revision THA.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

GeoGebra: A reliable and free software for measuring acetabular cup anteversion on digitalized plain radiographs

OBJECTIVE

Although accurate measurement of cup anteversion in hip replacement requires CT scans, however, its routine application, especially during follow-up, remains economically and ethically unreasonable. Thus, several methods have been devised for making this measurement on plain radiographs. In recent years, several ways have been adopted using software on digital radiographs. We present one such method which uses open access mathematical software GeoGebra.

METHODS

Anteversion was measured on 72 radiographs (36 cemented; 36 uncemented) by three different observers using this software. One observer repeated measurements at three weeks interval.

RESULTS

The intraclass correlation coefficient for interobserver variability and intraobserver variability was 0.982 (0.973-0.989) and 0.986 (0.978-0.991) respectively. There was a significant difference in the reliability of the method for cemented and uncemented cups with higher reliability for cemented cups (p < 0.001).

CONCLUSION

GeoGebra software can be used as a reliable alternative for measuring acetabular cup anteversion on good quality well centred digital radiographs of the pelvis.

Acetabular positioning is more consistent with the use of a novel miniature computer-assisted device

INTRODUCTION

Computer-assisted surgery (CAS) relying on registration of the anterior pelvic plane (APP) allows precise acetabular component placement. We determined the variability of cup placement in patients who underwent THA with and without the use of CAS that does not rely on the registration of APP.

METHODS

Fifty-one patients who underwent staged-bilateral THAs, one without CAS (control), and a subsequent one with CAS (study group), were included. Acetabular inclination and anteversion were measured on standardized post-operative radiographs. Variance in cup position and Lewinnek's zone proportionality were compared between the groups. Multiple regressions were performed to identify factors affecting variability in acetabular component placement.

RESULTS

The mean inclination for the control and study group was 42.7° (SD 4.5) and 42.5° (SD 2.9), respectively. The inclination variance was 20.5° and 8.2° respectively (p = < 0.001). Cup inclination was more consistent in the study than in the control group (deviation from the mean: 2.3° vs. 3.8°, p < 0.001). The mean anteversion for the control and the study group was 25.5° (SD 7.4) and 26.8° (SD 4.3), respectively. The anteversion variance was 54.2° and 18.2° respectively (p = <0.001). Consistency in cup anteversion was significantly improved with CAS (deviation from the mean: 3.4° vs. 5.8°; p = 0.002). Lewinnek's zone proportionality was not affected by the use of  CAS. In the linear regression analysis, CAS significantly increased consistency in cup inclination (p = 0.01). Patient's factors including BMI and laterality affected consistency of cup placement.

CONCLUSION

CAS without referencing the APP allows a more consistent orientation of the acetabular component when compared to freehand placement.

Radiographic assessment of the cup orientation after total hip arthroplasty: a literature review

Optimal acetabular cup orientation is of substantial importance to good long-term function and low complication rates after total hip arthroplasty (THA). The radiographic anteversion (RA) and inclination (RI) angles of the cup are typically studied due to the practicability, simplicity, and ease of interpretation of their measurements. A great number of methods have been developed to date, most of which have been performed on pelvic or hip anteroposterior radiographs. However, there are primarily two influencing factors for these methods: X-ray offset and pelvic rotation. In addition, there are three types of pelvic rotations about the transverse, longitudinal, and anteroposterior axes of the body. Their effects on the RA and RI angles of the cup are interactively correlated with the position and true orientation of the cup. To date, various fitted or analytical models have been established to disclose the correlations between the X-ray offset and pelvic rotation and the RA and RI angles of the cup. Most of these models do not incorporate all the potential influencing parameters. Advanced methods for performing X-ray offset and pelvic rotation corrections are mainly performed on a single pelvic AP radiograph, two synchronized radiographs, or a two-dimensional/three-dimensional (2D-3D) registration system. Some measurement systems, originally developed for evaluating implant migration or wear, could also be used for correcting the X-ray offset and pelvic rotation simultaneously, but some drawbacks still exist with these systems. Above all, the 2D-3D registration technique might be an alternative and powerful tool for accurately measuring cup orientation. In addition to the current methods used for postoperative assessment, navigation systems and augmented reality are also used for the preoperative planning and intraoperative guidance of cup placement. With the continuing development of artificial intelligence and machine learning, these techniques could be incorporated into robot-assisted orthopaedic surgery in the future.

A Novel Method for Correcting Pelvic Tilt on Anteroposterior Pelvic Radiographs

Background Anteroposterior (AP) pelvic radiographs remain the standard for pre- and postoperative imaging during total hip arthroplasty (THA), despite the known limitation of plain films, including the inability to adequately account for distortion caused by variations in pelvic orientation such as pelvic tilt. The purpose of this study was to develop a reliable method for correcting pelvic tilt on AP pelvic radiographs in patients undergoing THA. Methods CT scans from 20 patients/cadaver specimens (10 male, 10 female) were used to create 3D renderings, from which synthetic radiographs of each pelvis were generated. For each pelvis, 13 synthetic radiographs were generated, showing the pelvis at between -30° and 30° of pelvic tilt, in 5° increments. On each image, eight unique parameters/distances were measured to determine the most appropriate parameters for the calculation of pelvic tilt. The most reliable and accurate of these parameters was determined via regression analysis and used to create gender-specific nomograms from which pelvic tilt measurements could be calculated. The accuracy and reliability of the nomograms and correction method were subsequently validated using both synthetic radiographs (n=50) and stereoradiographic images (n=58). Results Of the eight parameters measured, the vertical distance between the superior margin of the pubic symphysis and the transischial line (PSTI) was determined to be the most reliable (r=-0.96, ICC=0.94). Using that parameter and applying the associated nomograms to 50 synthetic radiographs of random pelvic tilt, the mean difference between the actual pelvic tilt and that calculated using the correction method was 0.1°±5.1° (p=0.98, r=0.96). In 58 stereoradiographic images, the mean difference between actual and measured pelvic tilt was -0.2°±6.4° (p=0.74, r=0.77). The pooled results indicate no significant difference between actual (2.2°±13.9°) and measured pelvic tilt (2.1°±14.3°, p=0.93, r=0.91). No significant differences were noted based on gender. Conclusions Our method of correcting for pelvic tilt using the vertical distance from the pubic symphysis to the transischial line provides a reliable method for correcting for pelvic tilt on AP pelvic radiographs.

MRI Evaluation of Posterior Capsular Dehiscence After Posterior Approach Total Hip Arthroplasty

INTRODUCTION

To our knowledge, no previous study has evaluated the use of MRI to diagnose posterior capsule dehiscence after posterior approach total hip arthroplasty (THA) with capsular repair and its association with postoperative posterior hip dislocation.

METHODS

A retrospective chart review of patients who underwent posterior approach THA with capsulotomy repair was performed. Patients were identified who subsequently underwent MRI, and these studies were evaluated for signs of posterior capsular disruption. Each chart was then evaluated for episodes of postoperative hip dislocation.

RESULTS

Six hundred seventy-five patients were included in the retrospective review. Thirty-two patients (17 women [aged 37 to 78 years] and 15 men [aged 34 to 80 years]) met the inclusion criteria. Fifteen patients of 32 (48.4%) developed posterior capsule dehiscence after repair (group 1). Seventeen patients of 32 (51.6%) did not have MRI evidence of posterior capsule dehiscence (group 2). In group 1, 2 patients of 15 (13.3%) experienced a posterior hip dislocation. No group 2 patients experienced a posterior hip dislocation. Overall, only 2 patients of 32 (6.3%) developed posterior hip dislocations. In group 1, 12 patients of 15 (80%) developed dehiscence at the lateral capsule margin at the greater trochanter suture repair site. The two patients in group 1 with posterior hip dislocations displayed MRI evidence of capsular dehiscence in this region. Two patients of 15 (13.3%) in group 1 demonstrated dehiscence at the central third of the posterior capsule, whereas 1 patient of 15 (6.6%) in group 1 demonstrated dehiscence at the medial/acetabular margin. No significant difference was found between the dislocation rates between groups 1 and 2 (P = 0.212). The distribution of capsular dehiscence (lateral, middle, and medial capsule) in group 1 was significant (P = 0.0006).

DISCUSSION

MRI can effectively diagnose capsular dehiscence in patients who have undergone posterior THA. Most repaired capsules failed in the lateral repair region. MRI offers the potential to identify patients with a higher risk of implant dislocation.

LEVEL OF EVIDENCE

Therapeutic level III.

Constrained Liner Revision Is Less Effective With Each Subsequent Constrained Liner Revision at Preventing Instability

BACKGROUND

Constrained liners are used to treat recurring total hip arthroplasty dislocations in certain patients. Little is known about the fate of constrained liner revisions. The aim of this study is to evaluate the rate and survivorship free of revision for mechanical failure of constrained liners in patients who were revised to their first, second, and third constrained liners.

METHODS

From 1989 to 2016, using our institution's total joint registry, we identified 554 revisions to a first constrained liner. Of the 554, 40 had mechanical failure of their index constrained liner and had revision to a second constrained liner. Of the 40, 13 had mechanical failure of their second constrained liner and had revision to a third constrained liner. Patients included in the failure analysis had minimum 2-year follow-up, with a mean follow-up of 5.5 years.

RESULTS

In patients receiving their first, second, and third constrained liners, the survivorship free of revision for mechanical failure at 4 years was 90%, 52%, and 28%, respectively. Patients with a second and third constrained liner were more likely to have a revision for mechanical failure (second odds ratio 8, P < .0001; third odds ratio 10, P < .0001) compared to those receiving their first constrained liner. Using a different constrained liner did not decrease the risk of failure.

CONCLUSION

After revision to a second or third constrained liner there is high rate of mechanical failure. When a total hip arthroplasty becomes unstable after constrained liner, surgeons should exercise caution before revising to another constrained liner.

Long-Term Outcomes of Constrained Liners Cemented into Retained, Well-Fixed Acetabular Components

BACKGROUND

Cementation of a constrained liner is a viable option for treating instability after total hip arthroplasty (THA) when the acetabular component is well fixed and well aligned. However, concerns regarding long-term mechanical failure and recurrent instability remain. The aim of this study was to evaluate the long-term survivorship, complications, and clinical and radiographic outcomes of constrained polyethylene liners cemented into well-fixed acetabular components at the time of revision THA.

METHODS

We identified 125 cases in which a constrained liner of 1 design was cemented into a retained, osseointegrated acetabular component during revision THA between 1998 and 2006. The mean patient age at revision was 70 years. Mean follow-up was 7 years. Survivorship data, risk of instability, and clinical and radiographic outcomes were analyzed.

RESULTS

Survivorship free from revision for instability was 86% at 5 years and 81% at 10 years. Survivorship free from aseptic acetabular component revision was 78% at 5 years and 65% at 10 years, with the most common failure mechanism being dissociation of the constrained liner from the acetabular component. Survivorship free from revision for any reason was 76% at 5 years and 60% at 10 years. The most common complications were instability and periprosthetic joint infection, with cumulative incidences at 7 years of 18% and 11%, respectively. Harris hip scores did not significantly improve. Cup position did not affect implant survivorship or risk of dislocation.

CONCLUSIONS

Cementing a constrained liner into a retained acetabular shell at the time of revision THA has durable long-term results, with 8 in 10 patients free from instability at 10 years. Aseptic acetabular survivorship was worse (65%) at 10 years, primarily due to dissociation of the constrained liner from the acetabular component.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Accuracy of plain antero-posterior radiographic-based methods for measurement of acetabular cup version

INTRODUCTION

Acetabular cup version is crucial for successful total hip arthroplasty (THA). Many methods have been described for measurement of cup version angle. The aim of this study is to assess the accuracy of five commonly used methods for measurement of acetabular cup version in plain antero-posterior views of the pelvis and hip.

MATERIAL AND METHODS

Sixty primary THA cases were subjected postoperatively to plain A-P of the pelvis (AP-P), A-P view of the hip (AP-H), and computed tomography (CT) imaging. The acetabular cup version was measured in AP-P and AP-H by five methods (Lewinnek, Widmer, Hassan et al., Ackland et al., and Liaw et al.). These measurements were compared to the CT measurement.

RESULTS

All plain X-ray methods showed no significant differences from the CT, except those of Hassan et al. in AP-H, and Widmer and Ackland et al. in AP-P.

CONCLUSIONS AND RECOMMENDATIONS

For measurement of acetabular cup version angle, we recommend the use of Lewinnek and Liaw et al. methods both in AP-P and in AP-H, while Hassan et al.'s method is recommended in AP-P only, and Widmer and Ackland et al.'s methods in AP-H only.

A mathematical method for precisely calculating the radiographic angles of the cup after total hip arthroplasty

We established a mathematical method to precisely calculate the radiographic anteversion (RA) and radiographic inclination (RI) angles of the acetabular cup based on anterior-posterior (AP) pelvic radiographs after total hip arthroplasty. Using Mathematica software, a mathematical model for an oblique cone was established to simulate how AP pelvic radiographs are obtained and to address the relationship between the two-dimensional and three-dimensional geometry of the opening circle of the cup. In this model, the vertex was the X-ray beam source, and the generatrix was the ellipse in radiographs projected from the opening circle of the acetabular cup. Using this model, we established a series of mathematical formulas to reveal the differences between the true RA and RI cup angles and the measurements results achieved using traditional methods and AP pelvic radiographs and to precisely calculate the RA and RI cup angles based on post-operative AP pelvic radiographs. Statistical analysis indicated that traditional methods should be used with caution if traditional measurements methods are used to calculate the RA and RI cup angles with AP pelvic radiograph. The entire calculation process could be performed by an orthopedic surgeon with mathematical knowledge of basic matrix and vector equations.

What Safe Zone? The Vast Majority of Dislocated THAs Are Within the Lewinnek Safe Zone for Acetabular Component Position

BACKGROUND

Numerous factors influence total hip arthroplasty (THA) stability including surgical approach and soft tissue tension, patient compliance, and component position. One long-held tenet regarding component position is that cup inclination and anteversion of 40° ± 10° and 15° ± 10°, respectively, represent a "safe zone" as defined by Lewinnek that minimizes dislocation after primary THA; however, it is clear that components positioned in this zone can and do dislocate.

QUESTIONS/PURPOSES

We sought to determine if these classic radiographic targets for cup inclination and anteversion accurately predicted a safe zone limiting dislocation in a contemporary THA practice.

METHODS

From a cohort of 9784 primary THAs performed between 2003 and 2012 at one institution, we retrospectively identified 206 THAs (2%) that subsequently dislocated. Radiographic parameters including inclination, anteversion, center of rotation, and limb length discrepancy were analyzed. Mean followup was 27 months (range, 0-133 months).

RESULTS

The majority (58% [120 of 206]) of dislocated THAs had a socket within the Lewinnek safe zone. Mean cup inclination was 44° ± 8° with 84% within the safe zone for inclination. Mean anteversion was 15° ± 9° with 69% within the safe zone for anteversion. Sixty-five percent of dislocated THAs that were performed through a posterior approach had an acetabular component within the combined acetabular safe zones, whereas this was true for only 33% performed through an anterolateral approach. An acetabular component performed through a posterior approach was three times as likely to be within the combined acetabular safe zones (odds ratio [OR], 1.3; 95% confidence interval [CI], 1.1-1.6) than after an anterolateral approach (OR, 0.4; 95% CI, 0.2-0.7; p < 0.0001). In contrast, acetabular components performed through a posterior approach (OR, 1.6; 95% CI, 1.2-1.9) had an increased risk of dislocation compared with those performed through an anterolateral approach (OR, 0.8; 95% CI, 0.7-0.9; p < 0.0001).

CONCLUSIONS

The historical target values for cup inclination and anteversion may be useful but should not be considered a safe zone given that the majority of these contemporary THAs that dislocated were within those target values. Stability is likely multifactorial; the ideal cup position for some patients may lie outside the Lewinnek safe zone and more advanced analysis is required to identify the right target in that subgroup.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Experimental study of the installation acetabular component with uncoverage in arthroplasty patients with severe developmental hip dysplasia

PURPOSE

The purpose of this study was stimation of optimal percentage of lateral uncoverage of the acetabular component during total hip arthroplasty for patients with severe developmental hip dysplasia.

METHODS

Mathematical computer modeling based on the finite element technique and the mechanical experiment were performed. Critical values of uncoverage enabling safe primary fixation of acetabular component were estimated in designed models.

RESULTS

Using the finite element technique and the mechanical experiment on pelvis models, a possibility of mounting an acetabular component with moderate uncoverage within 25% without screws and with significant uncoverage to 35% with an additional two-screw fixation was demonstrated.

CONCLUSIONS

This study provides additional guidance on optimal acetabular uncoverage assessment and fixation methods of surgeons performing THA on patients with DDH.