How superior placement of the joint center in hip arthroplasty affects the abductor muscles

Outcomes of a Double-Cup Construct to Treat Paprosky 3A and 3B Acetabular Defects at a Mean of 39 Months

BACKGROUND

Modular reconstruction systems based on porous tantalum (PT) prosthetic components have been increasingly used for the treatment of complex acetabular bone defects in revision total hip arthroplasty (rTHA). We report a novel technique that applies a revision cup as a "super-augment" to form a "double-cup" construct for Paprosky type III defects.

METHOD

A retrospective review was conducted on rTHA cases, comparing those treated with double-cup constructs (DC group, n = 48) to those treated with PT shells and augments (PT group, n = 48). All procedures were performed at the same institute between 2017 and 2022. Clinical outcome evaluation utilized the Harris Hip Score (HHS), Oxford Hip Score (OHS), and 36-Item Short Form Survey (SF-36). Preoperative and postoperative radiographic assessments measured hip center of rotation (COR) position and leg length discrepancy (LLD). Additionally, postoperative complications and implant survivorship were monitored during the follow-up period.

RESULTS

The clinical outcomes improved substantially in both groups, which showed no significant difference in HHS (P = 0.786), OHS (P = 0.570), and SF-36 (P = 0.691). Compared to the PT group, the reconstruction COR was significantly closer to the anatomic COR (vertical distance: 2.630 versus 7.355 mm, P = 0.0034; horizontal distance: 1.881 versus -6.413 mm, P < 0.0001) in Paprosky IIIB type defects. Additionally, postoperative LLD was less in the DC group (-8.252 versus -1.821 mm, P = 0.0008). Dislocation was the main complication in the DC group, and only one patient received re-revision due to repeated dislocation. The cumulative survival rate of the DC group (100%; 95% CI [confidence interval] 100) was better than the PT group (83.4%; 95% CI 70.5 to 98.6) when re-revisions for aseptic loosening were the endpoint (P = 0.046).

CONCLUSIONS

The double-cup construct is a reliable revision technique for the reconstruction of Paprosky type III bone defects. Although dislocation remains challenging, the biomechanically superior restoration achieved by this technique lowers the risk of aseptic loosening.

Postoperative hip center position is associated with gait symmetry in range of axial rotation in dysplasia patients after THA

Background

This study aimed to explore whether pre- or postoperative hip structures or surgical changes significantly influence hip range of motion (ROM) symmetry in patients with hip dysplasia during gait after total hip arthroplasty (THA) and provide possible surgical suggestions.

Methods

Fourteen patients with unilateral hip dysplasia underwent computed tomography before and after surgery to create three-dimensional hip models. Pre- and postoperative acetabular and femoral orientations, hip rotation centers (HRC), and femoral lengths were measured. Bilateral hip ROM during level walking after THA was quantified using dual fluoroscopy. The ROM symmetry in flexion-extension, adduction-abduction, and axial rotation was calculated using the symmetry index (SI). The relationship between SI and the above anatomical parameters and demographic characteristics was tested using Pearson's correlation and linear regression.

Results

The average SI values for flexion-extension, adduction-abduction, and axial rotation during gait were -0.29, -0.30, and -0.10, respectively. Significant correlations were detected mainly in the postoperative HRC position. A distally placed HRC was associated with increased SI values for adduction-abduction (R = -0.47, p = 0.045), while a medially placed HRC was associated with decreased SI values for axial rotation (R = 0.63, p = 0.007). A regression analysis indicated that horizontal HRC positions significantly determined axial rotational symmetry (R² = 0.40, p = 0.015). Normal axial rotation SI values were achieved with HRC between 17 mm medially and 16 mm laterally.

Conclusions

Postoperative HRC position was significantly correlated with gait symmetry in the frontal and transverse planes in patients with unilateral hip dysplasia after THA. Surgical reconstruction of the HRC to between 17 mm medially and 16 mm laterally may contribute to gait symmetry.

Extended Fixation for Paprosky Type III Acetabular Defects in Revision Total Hip Arthroplasty with a Minimum Follow-Up of 2 Years

OBJECTIVE

Revision of total hip arthroplasty for patients with severe acetabular bone defects is challenging. This study aims to report the minimum 2 years outcome of the iliac extended fixation technique in patients with Paprosky type III acetabular defects.

METHODS

Fifty-seven revision total hip arthroplasty patients were retrospectively reviewed who underwent reconstruction with the concept of iliac extended fixation from 2014 to 2017 in our hospital. We proposed a new concept of "iliac extended fixation" in revision total hip arthroplasty as fixation extending superiorly 2 cm beyond the original acetabular rim with porous metal augments, which was further classified into intracavitary and extracavitary fixation. Patients were assessed using the Harris Hip Score and the Western Ontario and McMaster Universities Osteoarthritis Index Score. Radiographs and patient-reported satisfaction were assessed.

RESULTS

At an average follow-up of 63 months (range 25-88 months), the postoperative Harris Hip Score and Western Ontario and McMaster Universities Osteoarthritis Index scores were significantly improved at the last follow-up (p < 0.001). The center of rotation was significantly improved (p < 0.05). Fifty-three (93.0%) patients were satisfied with the outcome. The extracavitary iliac extended fixation group had higher rate of osteointegration in zone 1A (the superior lateral zone) than the intracavitary iliac extended fixation group (82.3% vs 55.0%, p = 0.015), and significantly more horizontal screws fixation (5.1 ± 24.7° vs 42.3 ± 36.8°, p < 0.001).

CONCLUSION

Intracavitary and extracavitary iliac extended fixation with porous metal augments and cementless cups are effective in reconstructing severe superior acetabular bone defects. The difference in screw direction might reflect the different biomechanics of augment fixation.

Acetabular reconstruction with femoral head autograft in primary total hip arthroplasty through a direct anterior approach is a reliable option for patients with secondary osteoarthritis due to developmental dysplasia of the hip

BACKGROUND

Developmental dysplasia is challenging to treat with total hip arthroplasty via the direct anterior approach (DAA). Reconstructing the former anatomy while restoring the acetabular bone stock for future revisions in this young patient collective combined with the known advantages of the DAA would be desirable. The purpose of this study was to analyze the feasibility, radiographic outcome and clinical outcome of primary uncemented total hip arthroplasty with bulk femoral head autograft for acetabular augmentation through a DAA with a minimal follow-up of 12 months.

METHODS

A retrospective, consecutive series from March 2006 to March 2018 of 29 primary total hip arthroplasty with acetabular augmentation with bulk femoral head autograft through a direct anterior approach was identified. All complications, reoperations and failures were analyzed. Radiographic and clinical outcome was measured.

RESULTS

24 patients (29 hips) with a mean age of 43 (18-75) years and a mean follow-up of 35 months (12-137) were included. Surgical indication was secondary osteoarthritis for developmental dysplasia of the hip (Hartofilakidis Grade A (n = 19), B (n = 10)) in all cases. We noted no conversion of the approach, no dislocation and no acetabular loosening. The center of rotation was significantly distalized by a mean of 9 mm (0-23) and significantly medialized by a mean of 18 mm (6-29). The bone graft was fully integrated after 12 months in all cases.

CONCLUSION

Acetabular reconstruction with femoral head autograft in primary THA through a direct anterior approach seems to be a reliable option for the treatment of secondary osteoarthritis in patients with DDH Hartofilakidis grade A and B. Prospective cohort studies with a large sample population and a long-term follow-up are necessary to confirm our findings.

Clinical and Radiological Outcomes of Revision Total Hip Arthroplasty for Patients with Prior Hartofilakidis Type C Hip Dysplasia

OBJECTIVE

To investigate the clinical and radiological results of revision total hip arthroplasty (THA) for patients with previously diagnosed Hartofilakidis type C hip dysplasia, which is technically challenging and lacks literature.

METHODS

We enrolled 20 patients with previously diagnosed Hartofilakidis type C hip dysplasia who underwent revision THA between November 2008 and July 2015 at our hospital. Patients were followed up for an average of 87 months. Data pertaining to the Harris hip score (HHS), modified Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), general satisfaction, and the level of satisfaction related to 16 hip functions or issues experienced after revision THA were collected. The vertical and horizontal center of rotation (COR) of the hips were measured bilaterally based on preoperative and postoperative anteroposterior radiographs. Categorical variables were analyzed by the chi-square test. Continuous variables were analyzed using the student's t test or non-parametric Wilcoxon Rank Sum test.

RESULTS

There were significant postoperative improvements in the HHS (47.4 ± 31.6 vs 70.1 ± 39.0), modified WOMAC (48.5 ± 27.9 vs 75.7 ± 36.8), and the vertical (45.7 ± 33.7 mm vs 21.6 ± 21.8 mm) and horizontal (41.8 ± 17.0 mm vs 31.4 ± 14.7 mm) offset of the COR after revision THA (P < 0.05). Fifteen (75.0%) patients were satisfied with the procedure. The satisfaction rate for each of the 16 items ranged from 45% to 100%. The top three dissatisfactory items were squatting, getting into/out of cars, and leg-length discrepancy. Postoperatively, dissatisfied patients had a significantly higher visual analogue scale pain score and lower WOMAC pain, HHS pain, WOMAC total, and HHS total scores, a lower satisfaction rate for pain relief, and a higher vertical COR.

CONCLUSION

There is a high rate (25%) of dissatisfaction with the outcome after revision THA for patients with prior Hartofilakidis type C hip dysplasia. The most likely reasons for dissatisfaction were inadequate pain relief and a higher vertical COR measured on radiography.

Meta-analysis of the Efficacy of the Anatomical Center and High Hip Center Techniques in the Treatment of Adult Developmental Dysplasia of the Hip

Background. In total hip arthroplasty for the treatment of adult developmental dysplasia of the hip, there is considerable controversy regarding the placement of the acetabular cup, anatomic center, and upward in acetabular reconstruction. This article explores the efficacy of the anatomical center technique and high hip center technique in the treatment of adult developmental dysplasia of the hip. Method. By searching for articles in the Cochrane Library, PubMed, CNKI, and Wanfang databases, we collected the literature on the treatment of adult developmental dysplasia of the hip by anatomical center and high hip center technology and screened the literature according to the inclusion and exclusion criteria. The Cochrane risk of bias assessment tool was used to assess the risk of bias of randomized controlled trials, the quality of the literature in retrospective cohort studies was assessed using the Newcastle–Ottawa scale, and the RevMan 5.4 software was used to analyze the extracted outcome indicators. Results. Nine studies were finally included, including one prospective cohort study, eight retrospective cohort studies, two high-quality studies, and six moderate-quality studies. The meta-analysis results showed that the reconstruction of the acetabulum in two positions was significantly different in terms of operation time ( $\text{WMD}=-37$ , 95% CI: -45.25-28.74, $P<0.00001$ ), intraoperative blood loss ( $\text{WMD}=-91.88$ , 95% CI: -108.57-75.19, $P<0.00001$ ), postoperative drainage volume ( $\text{WMD}=80.55$ , 95% CI: -140.56-301.66, $P=0.48$ ), time to ground ( $\text{WMD}=-0.68$ , 95% CI: -1.37-0.0, $P=0.05$ ), Harris score ( $\text{WMD}=-0.04$ , 95% CI: -0.91-0.82, $P=0.92$ ), lower limb length difference ( $\text{WMD}=0.21$ , 95% CI: -0.22-0.64, $P=0.33$ ), WOMAC score ( $\text{WMD}=-1.24$ , 95% CI: -4.89-2.41, $P=0.51$ ), postoperative complications ( $\text{RD}=-0.02$ , 95% CI: -0.06-0.02, $P=0.44$ ), Trendelenburg sign ( $\text{RD}=-0.02$ , 95% CI: -0.02-0.05, $P=0.31$ ), limb lengthening ( $\text{WMD}=0.85$ , 95% CI: 0.61-1.09, $P<0.00001$ ), prosthesis wear ( $\text{WMD}=0.01$ , 95% CI: 0-0.02, $P=0.17$ ), and prosthesis loosening ( $\text{RD}=0.01$ , 95% CI: -0.02-0.04, $P=0.45$ ). Conclusions. The high hip center technique can reduce operative time, intraoperative blood loss, and downtime. The anatomical center technique is superior to the high hip center technique in terms of limb lengthening. Compared with acetabular anatomical reconstruction, there was no significant difference in postoperative drainage, lower limb length difference, postoperative complications, Trendelenburg sign, and prosthesis survival or wear. For DDH patients who are not severely shortened in the lower limbs and have severe acetabular bone defects, joint surgeons can choose to reconstruct the acetabulum in the upper part to simplify the operation, reduce the trauma of the patient, and accelerate the recovery of the patient, and they can choose to adjust the length of the neck and the angle of the neck shaft to maintain the moment arm of the abductor muscle. A ceramic interface or a highly cross-linked polyethylene interface minimizes the effect of hip response forces. To further evaluate the efficacy of the anatomical center technique and the high hip center technique in the treatment of adult developmental dysplasia of the hip, more large-sample, high-quality, long-term follow-up randomized controlled trials are still needed for verification.

The optimal screw-hole positions of the eccentric revision cup based on a morphological study

Background

Bridging bone defects in revision total hip arthroplasty is a challenge to orthopedic surgeons. The eccentric revision cup is a progression of jumbo cup. Our aim is to confirm the optimal screw-hole positions of the eccentric revision cup by morphological measurements of three-dimensional pelvic reconstruction.

Methods

Eighty CT images were converted to virtual three-dimensional bones. After simulating the surgery procedure, all available screw holes were inserted with the screws in virtual. By measuring the length of the screw in the pelvic bone, we determined the rich bone stock area. Then the screw holes were designed according to the characteristics of bone stock distribution. The peripheral screw-hole cluster and inner screw-hole cluster were studied respectively.

Results

For peripheral screw-hole cluster, five screw holes were evenly distributed between point A and point B in the thicker rim. For inner screw-hole cluster, screw hole 1 and screw hole 2 are the recommended inner screw holes.

Conclusion

The eccentric revision cup has inherited the strengths of jumbo cup besides several unique advantages, including using the peripheral screws enhancing primary stability; decreasing the shift of hip rotation center and restoring biomechanical function; reducing the risk of dislocation because of the smaller head-cup differences; increasing the contact area between the outer cup and the host bone while maintaining a normal inclination of the inner cup. In this study, we confirmed the optimal screw-hole positions of the eccentric revision cup by surgical simulation and morphological measurement. However, biomechanical tests are still being further explored.

The application of custom-made 3D-printed titanium augments designed through surgical simulation for severe bone defects in complex revision total hip arthroplasty

Background

With the development of radiology and three-dimensional (3D) printing technology, custom-made 3D-printed titanium augments have been more widely used. However, the radiological and clinical outcomes of custom-made augments lack reports. To better understand the clinical effect of using 3D-printed titanium augments and the significance of accurate placement, the aim of this study was to assess the outcomes when using custom-made 3D-printed titanium augments and to validate the idea that surgical simulation should be done before designing custom-made augments.

Methods

A retrospective review was conducted on 31 surgical simulations and revision total hip arthroplasties using custom-made 3D-printed titanium augments. The safe zone, cup position, and hip rotation center were measured on anteroposterior radiographs. Clinical outcomes were assessed with a mean 21.1 months of follow-up.

Results

All patients were positioned within the safe zone, and none of the acetabular cups nor the custom-made augments had any evidence of migration at the latest follow-up. A strong correlation was found between the planned cup position and the postoperative position. The average vertical position of the center of rotation was significantly increased from 3.55 cm to 2.35 cm. The mean Harris Hip Score was increased from 40.81 preoperatively to 65.46 postoperatively. Complications included gait abnormality, groin pain, fracture of the greater trochanter, and partial palsy of the sciatic nerve. However, patient satisfaction reached 92.3%.

Conclusion

Surgical simulations help to design custom-made augments accurately and improve surgical plans. Acetabular components supported with custom-made 3D-printed augments is a useful method to bridge severe bone deficiencies. In this study, both the radiologic results and clinical outcomes were favorable.

Level of evidence

Level 4.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10195-022-00656-5.

A single-surgeon experience in reconstruction of femoro-acetabular offset and implant positioning in direct anterior approach and anterolateral MIS approach with a curved short stem

PURPOSE

Minimally invasive surgery using short stems in total hip arthroplasty gained more popularity. The differences in change of hip offset and implant positioning in minimally invasive approaches are not fully known. Therefore, this study was conducted to evaluate the difference in reconstruction of hip offset and implant positioning in direct anterior approach (DAA) and minimally invasive anterolateral approach (AL MIS).

METHODS

A single surgeon series of 117 hips (117 patients; mean age 65.54 years ± 11.47; index surgery 2014-2018) were included and allocated into two groups: group A (DAA) with 70 hips and Group B (AL MIS) with 47 patients operated. In both groups the same type of cementless curved short hip stem and press fit cup was used.

RESULTS

Both groups showed an equal statistically significant increase of femoral (p < 0.001) and decrease of acetabular offset (p < 0.001). Between both groups no statistically significant difference in offset reconstruction, leg length difference or implant positioning could be found. Leg length increased in both groups significantly and leg length discrepancy showed no difference (group A: - 0.06 mm; group B: 1.11 mm; p < 0.001). A comparable number of cups were positioned outside the target zone regarding cup anteversion.

CONCLUSION

The usage of a curved short stem shows an equal reconstruction of femoro-acetabular offset, leg length and implant positioning in both MIS approaches. The results of this study show comparable results to the existing literature regarding change of offset and restoration of leg length. Malposition of the acetabular component regarding anteversion poses a risk.

Acetabular Revision Arthroplasty Based on 3-Dimensional Reconstruction Technology Using Jumbo Cups

Background: This study was aimed at evaluating the changes in cup coverage (CC) and hip center of rotation (HCOR) in acetabular defects of various severities treated with acetabular revision using jumbo cups.

Methods: A total of 86 hips were included. The American Academy of Orthopedic Surgeons (AAOS) classification of these patients was as follows: 16 patients, AAOS I; 16 patients, AAOS II; and 16 patients, AAOS III. A three-dimensional (3D) implant simulation technique was used to visualize the placement of jumbo cups during revision arthroplasty. The acetabular anteversion, inclination, CC, and the HCOR were measured.

Results: The inclination and anteversion of simulated acetabular cups in AAOS I–III groups were consistent with the normal acetabular anatomy. Compared with the controls, in AAOS I–III groups, the HCOR was significantly increased and CC was significantly decreased. The HCOR elevation was significantly higher in AAOS III patients than in AAOS I (p = 0.001) and AAOS II patients (p < 0.001). The use of the jumbo cup technology for acetabular revision would decrease the CC in AAOS I–III patients to 86.47, 84.78, and 74.51%, respectively.

Conclusion: Our study demonstrated that in patients with acetabular defects, acetabular revision arthroplasty using jumbo cups will lead to decreased CC and HCOR upshift. Upon classifying these patients according to the AAOS classification, CC decreased with the severity of acetabular defects, and the elevation of the HCOR in AAOS III patients exceeded 10 mm and was significantly higher than in other patients.

Femoral Head Autograft Can Reliably Reconstruct Dysplastic Acetabula Through the Direct Anterior Approach for Total Hip Arthroplasty

Background

Bone deficiencies in dysplastic acetabula create technical difficulties during total hip arthroplasty (THA). Bulk femoral head autograft (FHA) is one method to increase cup coverage and bone stock of the true acetabulum; however, only limited data exist on its efficacy through a direct anterior approach (DAA). This study aimed to evaluate the outcomes of FHA during THA via a DAA in dysplastic hips.

Methods

Retrospective review of 34 patients (41 hips) with hip dysplasia (Crowe I-III) who underwent primary THA via a DAA with FHA at a single institution was performed. Surgical procedures were performed on a traction table with intraoperative fluoroscopy and highly porous-coated cup placement in the true acetabulum. Patients were assessed clinically and radiographically at a minimum of 2 years postoperatively (range, 2 to 7).

Results

The average modified Harris Hip Score improved from 31.9 ± 10.8 to 94.1 ± 5.8, Merle d'Aubigné Hip Score from 7.5 ± 2.8 to 16.6 ± 1.1, and visual analog pain score from 7.9 ± 2.7 to 1.4 ± 1.4 (all P < .001). All hips had an “anatomic” inferomedial cup position postoperatively, with an average increase in horizontal coverage of 43.4%. Mean postoperative limb-length discrepancy improved from 21.8 ± 16.1 mm to 1.6 ± 5.7 mm (P < .001). There were no cases of revision THA, nor complications such as dislocation, infection, or osteolysis.

Conclusion

Reconstructing dysplastic acetabula (Crowe I-III) with FHA during THA can be successfully accomplished via the DAA with increased acetabular bone stock and accurate correction of limb-length discrepancy.

High hip center arthroplasty in the treatment of severe hip dysplasia: Are knee and ankle compromised?

BACKGROUND

There is limited information about the effect of hip center location on gait parameters of knee and ankle. This study aimed to compare anatomical vs. high hip center arthroplasty according to gait parameters of knee and ankle and investigate whether the high hip center has any adverse effect on these joints or not.

METHODS

20 patients who underwent unilateral total hip arthroplasty (Group 1; 10 patients with anatomical reconstruction, Group 2; 10 patients with high hip center) due to Crowe type III-IV developmental dysplasia of the hip and completed 2 years of follow-up were included. The patients were examined by 3-D gait analysis.

FINDINGS

The maximum extension of the knee on the operated side was lower in Group 2 (p = 0.044). Longitudinal knee joint force was higher in Group 2 on both operated (p = 0.041) and non-operated sides (p = 0.031). Lateral knee joint force was also higher in Group 2 (p = 0.023). No significant difference was detected in ankle parameters.

INTERPRETATION

Unilateral high hip center has been shown to restrict the dynamic knee range of motion on the operated side and increase the knee load on both sides, thus putting the knees at risk for osteoarthritis.

LEVEL OF EVIDENCE

Level III, Retrospective comparative study.

The accuracy of digital templating in cementless total hip arthroplasty in dysplastic hips

Background

Total hip arthroplasty (THA) for developmental dysplasia of the hip (DDH) is a complex procedure due to associated anatomical abnormalities. We studied the extent to which preoperative digital templating is reliable when performing cementless THA in patients with DDH.

Methods

We templated and compared the pre- and postoperative sizes of the acetabular and femoral components and the center of rotation (COR), and analysed the postoperative cup coverage, leg length discrepancy (LLD), and stem alignment in 50 patients (56 hips) with DDH treated with THA.

Results

The implant size exactly matched the template size in 42.9% of cases for the acetabular component and in 38.2% of cases for the femoral component, whereas the templated ±1 size was used in 80.4 and 81.8% of cases for the acetabular and femoral components, respectively. There were no statistically significant differences between templated and used component sizes among different DDH severity levels (acetabular cup: p = 0.30 under the Crowe classification and p = 0.94 under the Hartofilakidis classification; femoral stem: p = 0.98 and p = 0.74, respectively). There were no statistically significant differences between the planned and postoperative COR (p = 0.14 horizontally and p = 0.52 vertically). The median postoperative LLD was 7 (range 0–37) mm.

Conclusion

Digital preoperative templating is reliable in the planning of cementless THA in patients with DDH.

Comparison of sliding distance of lag screw and nonunion rate according to anteromedial cortical support in intertrochanteric fracture fixation: A systematic review and meta-analysis

INTRODUCTION

We compared the sliding distance of the lag screw, change in neck-shaft angle (NSA), and nonunion rates according to the anteromedial cortical support on anteroposterior (AP) and lateral view radiographs post intertrochanteric fracture reduction.

MATERIAL AND METHODS

In this systematic review and meta-analysis, MEDLINE, Embase, and Cochrane Library databases were searched systematically for studies published before September 26, 2020. We performed synthetic analyses of the amount of lag screw sliding, change in NSA, and incidence of nonunion following reduction of intertrochanteric fractures by extramedullary reduction (EMR), neutral reduction (NR), and intramedullary reduction (IMR). The combined data of EMR and NR comprised the non-IMR group.

RESULTS

Our study enrolled eight studies, representing 1,363 patients who underwent surgery for intertrochanteric fractures. A pooled analysis showed a larger sliding distance in the IMR group than in the non-IMR group (standard mean difference [SMD] = 1.47, 95% confidence interval [CI]: 0.73-2.20; P < 0.0001 and SMD = 1.27, 95% CI: 0.56-1.99; P = 0.0005, respectively) in both AP and lateral views. The pooled mean difference of change in NSA in the IMR group was -3.11° and differed significantly from that of the non-IMR group (95% CI: -4.07 to -2.16; P < 0.0001). In the lateral view, the nonunion rate was significantly higher in the IMR group than in the non-IMR group (odds ratio [OR] = 11.61; 95% CI, 3.32-40.62; P = 0.0001). In the subgroup analysis, the NR group showed a larger sliding distance than that of the EMR group in the AP view (SMD = 0.40, 95% CI: 0.04-0.76; P = 0.03); however, the reverse was true in the lateral view (SMD = 0.68, 95% CI: 0.38-0.97; P < 0.00001).

CONCLUSION

In the current meta-analysis, larger sliding distances, more varus in NSA, and higher nonunion rates were observed in the IMR group than the non-IMR group, in both AP and lateral views. However, in the comparison between EMR and NR, it was difficult to conclude which of them was the ideal reduction method because of inconsistent results.

Interobserver and Intraobserver Reliabilities of Three-Dimensional Postoperative Evaluation Software in Total Hip Arthroplasty

BACKGROUND

In primary and revision total hip arthroplasty, to prevent perioperative complications, the prediction of the optimal implant size is essential. Using three-dimensional computed tomography-based postoperative evaluation software, we explored the accuracy and the precision of measurement of the size, alignment, and position of the prosthetic components after total hip arthroplasty.

METHODS

Using postoperative evaluation software, the postoperative computed tomography data from 20 hips in 20 patients were evaluated. The component size, alignment, and three-dimensional positioning of the cup and stem were assessed. The concordance rates of the component, repeatability (intraobserver reliability), and reproducibility (interobserver reliability) of postoperative evaluation were calculated. The radiographic inclination and radiographic anteversion of the cup, anteversion, varus-valgus angle, and flexion-extension angles of the stem were measured for alignment. The implant positioning was measured along three axes, namely, X-axis (transverse), Y-axis (sagittal), and Z-axis (longitudinal).

RESULTS

The concordance rates of all parts are above 94%. The intraobserver and interobserver intraclass correlation coefficients of alignment measurement were very good for both cup (0.879-0.964) and stem (0.973-0.996). The intraobserver and interobserver intraclass correlation coefficients of cup positioning were very good (0.961-0.987) for all axes. The intraobserver and interobserver intraclass correlation coefficients of implant positioning were very good for the stem (0.879-0.995) for all axes.

CONCLUSIONS

Computed tomography-based postoperative evaluation software was able to evaluate the size and position of total hip implants with high reproducibility.

Contact force path in total hip arthroplasty: effect of cup medialisation in a whole-body simulation

BACKGROUND

Cup medialisation down to the true acetabular floor in total hip arthroplasty with a compensatory femoral offset increase seems to be mechanically advantageous for the abductor muscles due to the relocation of the lever arms (body weight lever arm decreased, abductor lever arm increased). However, limited information is currently available about the effects of this reconstruction type at the head cup interface, compared to an anatomical reconstruction that maintains the natural lever arms. Through a whole-body simulation analysis, we compared medialised versus anatomical reconstruction in THA to analyse the effects on: (1) contact force magnitude at the head cup interface; (2) contact force path in the cup; and (3) abductor activity.

METHODS

Musculoskeletal simulations were performed to calculate the above-mentioned parameters using inverse dynamics analysis. The differences between the virtually implanted THAs were calculated to compare the medialised versus anatomical reconstruction.

RESULTS

Cup medialisation with compensatory femoral offset increase led to: (1) a reduction in contact force magnitude at the head cup interface up to 6.6%; (2) a similar contact force path in the cup in terms of sliding distance and aspect ratio; and (3) a reduction in abductor activity up to 17.2% (gluteus medius).

CONCLUSIONS

In our opinion, these potential biomechanical gains do not generally justify a fully medialised reconstruction, especially in younger patients that are more likely to undergo revision surgery in their lifetime. Cup medialisation should be performed until sufficient press fit and bony coverage of a properly sized and oriented cup can be achieved.

Jumbo cup in hip joint renovation may cause the center of rotation to increase

BACKGROUND

Utilizing the large jumbo cup in revision total hip arthroplasty is an effective approach to cure many lacunar and segmental peripheral bone defects. However, with the use of the jumbo cup, the center of the hip joint may become elevated relative to the primary acetabulum, and the diameter of the large cup is greater.

AIM

To study the height and the significance of the elevation of the hip joint center.

METHODS

Eighty-eight patients matched the criteria for this condition and were included in the study. The center height of the hip joint was measured relative to the opposite normal hip joint. The diameter of the jumbo cup was measured and checked according to operation notes, and the diameter of the jumbo cup was measured with a prosthesis label. Then, the horizontal and vertical centers of rotation were measured on the surgical side and opposite side. The average center height of the hip joint on the renovated side and the opposite side and the position of the hip cup relative to the teardrop were compared using a paired t-test.

RESULTS

Radiometric analysis showed that the average hip joint center was elevated by 7.6 mm. The rotational center height delta of the renovated hip was 7.6 ± 5.6 mm, and there was an obvious difference between the two groups (P = 0.00). The difference in horizontal distance was 0.5 ± 5.1 mm (-11.5 -14.0 mm), and there was no obvious difference between the two groups (P = 0.38). According to the foreign standard, the rotational center height delta of the renovated hip was 7.5 ± 6.2 mm, and there was a significant difference between the two groups (P = 0.00). There was no obvious difference between the domestic and foreign standards (P > 0.05) between the two groups.

CONCLUSION

The application of the jumbo cup elevates the rotational center of the hip joint, but it is feasible and effective to use the jumbo cup.

Postoperative radiographic evaluation and simulation study for optimal cup placement in high-hip centre total hip arthroplasty

BACKGROUND

Achieving favourable outcomes in high-hip centre reconstruction in hip dysplasia requires the optimal cup height and size, which can provide sufficient bone coverage for stable cup fixation that fits the anteroposterior acetabular rim without increasing the cup height more than necessary.

METHODS

We retrospectively reviewed 214 patients who underwent primary total hip arthroplasty (THA) and identified 30 hips with Crowe II (n = 15) or III (n = 15) developmental dysplasia of the hip (DDH). We measured the cup-centre-edge angle (cup-CE) and the vertical and horizontal distances from the teardrop. In a simulation study, we examined the cup-CE and optimal cup size by changing the cup height in 5-mm increments over a distance of 15-40 mm above the inter-teardrop line using a 3-dimensional template system.

RESULTS

Postoperative radiographic evaluation revealed a mean cup-CE of 19.9° in Crowe II hips and 15.2° in Crowe III hips; the respective mean vertical distances were 26.6 mm and 27.6 mm (p = 0.511). There was no evidence of cup loosening or lateralisation at a minimum of 7 years (7-11 years) follow-up. Simulation showed that the hip centre needed to be elevated to 20 mm to acquire a cup-CE of more than 0°. More than 10° of cup-CE could be expected by elevating the hip centre to 25 mm in both Crowe II and III.

CONCLUSIONS

Even in severe DDH, a high-hip centre positioned approximately 25 mm superior to the inter-teardrop line was sufficient to achieve optimal bone coverage, which could lead to more secure cup fixation.

Anterior Total Hip Arthroplasty With Bulk Femoral Head Autograft in a Patient With Camurati-Engelmann Disease

Camurati-Engelmann disease (CED) is an extremely rare, sclerosing bone disorder of intramedullary ossification with only 300 reported cases worldwide. The pathogenesis is related to activating mutations in transforming growth factor beta 1, which results in bilateral, symmetric hyperostosis affecting primarily the diaphysis of long bones. Despite effective pharmacological treatment options, the diagnosis of CED is problematic owning to its rarity and variability of clinical presentation. We present a patient with known CED with advanced early hip osteoarthritis, secondary to underlying hip dysplasia, for which she underwent a successful total hip arthroplasty via a direct anterior approach with the use of bulk femoral head autograft to reconstruct her native acetabulum.

Functional and radiographical results of asymmetrically reconstructed total hip arthroplasty in patients with bilateral dysplastic arthritic hips with one hip Crowe II-III and the other Crowe IV: a retrospective cohort study

Background

The study aimed to evaluate the functional and radiographical results of asymmetrically reconstructed total hip arthroplasty in patients with bilateral dysplastic arthritic hips with one hip Crowe II–III and the other hip Crowe IV.

Materials and methods

From April 2006 to April 2019, we evaluated 23 patients who had a reconstruction of one Crowe II–III hip with high hip center (HHC) and the other Crowe IV hip at the anatomical position (H group). The radiographic and clinical outcomes were compared with those of a control group of 19 patients with bilateral dysplasia who had one Crowe IV hip and the contralateral hip both reconstructed in the anatomical position (A group). Medical records and radiographs were reviewed, and a complete follow-up was conducted for all patients.

Results

The mean vertical center of rotation (V-COR) and horizontal center of rotation (H-COR) in the H group were 30.6 ± 5.8 mm and 30.0 ± 5.5 mm, respectively. In the A group, the corresponding values were 14.0 ± 4.3 mm and 23.0 ± 2.3 mm, respectively. A significant difference was found in terms of V-COR and H-COR between the two groups, and no significant difference was shown regarding the cup inclination, abductor lever arm (ALA), ALA ratio, and leg length discrepancy (LLD). Three patients of the H group and four patients of the A group exhibited LLD > 10 mm. All seven patients who had LLD > 10 mm underwent the shortening subtrochanteric osteotomy (SSTO) of the Crowe IV hip. Subgroup analysis based on the presence and absence of SSTO showed that the LLD of the SSTO group was greater than that of the non-SSTO group in both groups, but the difference was only statistically significant in the A group. At the last follow-up, the mean Harris Hip Scores significantly improved in the two groups, and there was no revision during the follow-up period. In the H group, four patients presented with a slight limp and three patients with a moderate limp, while it was six patients and one patient in the A group, respectively.

Conclusions

Asymmetrical reconstruction in patients with bilateral dysplastic arthritic hips with one hip Crowe II–III and the other Crowe IV is acceptable and comparable when compared with bilateral anatomical reconstruction.

Level of evidence

III, retrospective observational study.

Trial registration Chinese Clinical Trail Registry. ChiCTR2000033848

Restoration of the hip geometry after two-stage exchange with intermediate resection arthroplasty for periprosthetic joint infection

Two-stage exchange with intermediate resection arthroplasty (RA) is a well-established surgical procedure in the treatment of chronic periprosthetic joint infection (PJI), whereby a higher failure rate of final hip geometry restoration due to tissue contraction is controversially discussed. The aim was to evaluate radiographic changes of hip geometry parameters during PJI treatment and to determine the impact of the intermediate RA on the final joint restoration after reimplantation of a total hip arthroplasty (reTHA). Radiographic parameters (leg length (LL), femoral offset (FO), horizontal/vertical acetabular center of rotation distance (h/vCORD)) of 47 patients (mean age: 64.1 years) were measured on standard radiographs of the pelvis and compared between four different stages during PJI treatment (pre-replacement status (preTHA), primary total hip arthroplasty (pTHA), RA and reTHA). The RA duration (mean: 10.9 months) and the number of reoperations during this period (mean: n = 2.0) as well as their impact on hip geometry restoration were evaluated. Between preTHA and pTHA/reTHA an equivalent restoration was measured regarding the FO (p < 0.001/p < 0.001) and hCORD (p = 0.016/p < 0.001), but not regarding the LL and vCORD. In contrast, analysis revealed no influence of RA and an equivalent reconstruction of LL (p = 0.003), FO (p < 0.001), v/hCORD (p = 0.039/p = 0.035) at reTHA compared to pTHA. Furthermore, RA duration (p = 0.053) and the number of reoperations after RA (p = 0.134) had no impact on radiographic hip geometry restoration. The two-stage exchange with intermediate RA does not alter the preexisting hip joint parameters, whereby a good restoration of the final hip geometry, independent of the duration or the number of reoperations, can be achieved.

Relationship of the Pelvic-Trochanteric Index with greater trochanteric pain syndrome

OBJECTIVES

This study aimed to correlate a higher Pelvic-Trochanteric Index (PTI) with an increased varus of the femoral neck with greater trochanteric pain syndrome (GTPS). The secondary objective was to check whether the pelvic width changes with age.

METHODS

A prospective study was conducted to compare female patients diagnosed with GTPS (case group) with asymptomatic female participants (control group) from March 2011 to June 2017. On an anteroposterior pelvic radiograph, lines were drawn by two radiologists, and the PTI (ratio of the distance between the greater trochanters and distance between the iliac crests) was defined and the femoral neck-shaft angle was measured.

RESULTS

Data collected based on radiographs of 182 female patients (cases) and 150 female participants (controls) showed that the mean PTI was 1.09 (SD=0.01) in the case group and 1.07 (SD=0.01) in the control group (p<0.05), regardless of age. The distance between iliac crests increased with age (p<0.05) in symptomatic and asymptomatic individuals. It was also found that the mean femoral neck-shaft angle was 130.6° (SD=0.59) and progression of the varus angulation occurred with age in both groups, with a significance level of 5%.

CONCLUSIONS

The PTI was higher in patients with GTPS. The femoral neck-shaft angle does not differ between individuals with and without GTPS; however, it does decrease with age. The pelvic width tends to increase with aging in symptomatic or asymptomatic individuals; therefore, the increase in the pelvic width and decrease in the femoral neck-shaft angle can be interpreted as normal in aging women, which could alter the biomechanics of the hips and pelvis.

Effect of cup medialization on primary stability of press-fit acetabular cups

BACKGROUND

Appropriate restoration of the native centre of rotation is of paramount importance in total hip arthroplasty. Reconstruction of the centre of rotation depends on reaming technique: conventional approaches require more cup medialization than anatomical preparations. To date, the influence of cup medialization on socket stability in cementless implants is still unknown.

METHODS

Ten cadaveric hemipelvises were sequentially reamed using anatomical technique (only subchondral bone removal with restoration of the native centre of rotation) and conventional preparation (reaming to the lamina and medializing the cup). A biomechanical test was performed on the reconstructions. Implant motions were measured with digital image correlation while a cyclic load of increasing magnitude was applied.

FINDINGS

No significant difference was measured between the two implantation techniques in terms of permanent cup migrations. The only significant difference was found for the cup inducible rotations, where the conventional technique was associated with larger rotations.

INTERPRETATION

Conventional reaming and cup medialization do not improve initial cup stability. Beyond the recently questioned concerns about medialization and hip biomechanics, this is another issue to bear in mind when reaming the acetabulum.

The use of pelvic radiographs as a predictor for gluteal tendinopathy and bursitis

AIM

To evaluate the relationship between radiographic measurements of the hip and sonographic evidence of gluteal tendinopathy and bursitis in patients with lateral hip pain.

METHODS AND MATERIALS

Patients with lateral hip pain referred for ultrasound of the hip in our institution over a 5-year period were identified. Findings of gluteal tendinopathy and subgluteal or trochanteric bursitis on ultrasound were recorded. Radiographs of the hip were also evaluated and femoral offset (FO), global offset (GO), abductor lever arm (ALA) and trochanteric impingement distance (TID) were recorded. The mean of each measurement was compared between patients with gluteal tendinopathy and subgluteal or trochanteric bursitis.

RESULTS

273 patients were included in the study. 107 patients (39.2%) had a THA. In the asymptomatic hip, a range of normal measurements were obtained: FO 22.4-76.5 mm, GO 40.1-116.1 mm, ALA 45.0-98.4 mm and TID 13.8-63.1 mm. In the native hip and post THA, there was no statistically significant relationship between FO, GO, ALA and TID in patients with gluteal tendinopathy or trochanteric or subgluteal bursitis.

CONCLUSIONS

Lateral hip pain is a common presenting complaint in patients with hip pain and is reported in a small proportion of patients post THA. No statistically significant relationship was found between radiographic measurements and ultrasound findings in our patient cohort. However, we describe the range of measurements obtained from the normal asymptomatic hip in this large cohort of patients, which may aid in the evaluation and management of patients with lateral hip pain.

Who Restores Hip Biomechanics More Effectively after a Femoral Neck Fracture? Comparison of Total Hip Arthroplasties Performed by Either Hip Surgeons or Orthopaedic Residents

Background

This study aims to analyze the ability to restore hip biomechanics in patients who undergo total hip arthroplasty for displaced femoral neck fractures operated by either hip surgeons (HSs) or orthopaedic residents (ORs).

Methods

We retrospectively compared 95 patients treated by HSs (group A) with 110 patients treated by ORs (group B). Leg-length discrepancy, femoral offset (FO), center of rotation (COR), acetabular inclination, and acetabular anteversion were evaluated on postoperative radiographs using the healthy contralateral hip as control.

Results

The median leg-length discrepancy was 2 mm for both groups (P = .74). The leg length was increased in 54% of the HS group and 57% of the OR group (P = .13). The median FO difference of groups A and B were 7 mm and 5.5 mm, respectively (P = .14). FO was increased in 80% of the HS group and 69% of the OR group (P = .19). Median discrepancies of the horizontal and vertical CORs were not statistically relevant, with P-values of .69 and .14, respectively. The horizontal COR was slightly medialized in 58% of the HS group and 53% of the OR group (P = .003). The vertical COR was slightly proximal in 66% of the HS group and 76% of the OR group (P = .28). The median acetabular inclination angles of groups A and B were 41° and 40°, respectively (P = .62). The median anteversion angle was 19° for both groups (P = .89).

Conclusions

The horizontal COR was the only measurement with statistical significance. To conclude, ORs under supervision are as reliable as HSs to properly restore hip biomechanics in patients who undergo total hip arthroplasty for displaced femoral neck fractures.

Biomechanical reconstruction parameters obtained after direct anterior approach total hip arthroplasty do not compromise clinical outcome

INTRODUCTION

Accurate reconstruction of biomechanical parameters following total hip arthroplasty (THA) is crucial for good joint function. We investigated how reconstruction parameters achieved by minimally invasive anterior (MIS) THA may influence function and patient-related outcomes.

METHODS

A consecutive series of 95 patients treated by MIS THA for primary osteoarthritis were retrospectively reviewed. Primary outcome measures were Harris Hip Score (HHS), hip disability and osteoarthritis outcome score (HOOS) and EQ-5D. Femoral offset (FO), abductor lever arm (ALA), centre of rotation (CoR), leg length discrepancy (LLD), cup version and stem alignment were measured pre- and post-operatively. Obtained reconstruction parameters compared to the contralateral hip were used as independent variables in a multivariate regression with each primary outcome measure as dependent variable.

RESULTS

Mean age at surgery was 69 years. HHS rated 94.7% of patients as good/excellent and mean EQ-5D was 0.82. Post-operative HOOS subscales showed no statistical difference compared to the Italian benchmark population. Stem alignment averaged 0.2° valgus, mean cup inclination was 37.8° and mean anteversion was 12.8°. When compared to the contralateral side, CoR was post-operatively elevated by 2.6 mm and medialized by 2.4 mm averagely. An average FO reduction of -0.5 mm was observed while FO ratio increased by 1.9% averagely. ALA decreased by -3.3 mm while LLD was 2.3 mm averagely. Multivariate regression analysis revealed a significant contribution of ALA to HHS only.

CONCLUSIONS

Biomechanical parameters achieved by MIS THA are satisfactory with negligible impact on functional results and no impact on patient-related outcomes certifying the high quality achieved in THA.

Surgical Approach and Reaming Depth Influence the Direction and Magnitude of Acetabular Center of Rotation Changes During Total Hip Arthroplasty

Background

Changes in acetabular or hip center of rotation (HCOR) commonly occur during acetabular component preparation during total hip arthroplasty (THA). HCOR displacement in mediolateral or superoinferior directions is known to influence offset and leg length, but the incidence and range of HCOR change in the anteroposterior direction is less understood as the sagittal plane cannot be measured on standard anteroposterior radiographs. This study assessed the 3-dimensional displacement of HCOR after cup implantation and evaluated for potential factors associated with increased acetabular component translations.

Methods

A total of 894 THAs were performed using a posterior, lateral, or direct anterior approach. Only intraoperative data from the navigation device were included in the analysis. All THAs performed between September 2015 and October 2017 were included. Paired t-tests were used to compare native HCOR and new HCOR values.

Results

The mean HCOR displacement in 3 directions was 4.97mm medially (P < .001), 0.83mm superiorly (P < .001), and 0.64mm posteriorly (P < .001). Subgroup analysis revealed greater posterior HCOR displacement with the anterior approach than the lateral/posterior approach (2.32mm vs 0.44mm; P < .001). Increasing medial HCOR displacement also resulted in increased superior and posterior HCOR displacement across surgical cases (P < .001).

Conclusions

HCOR displacement is commonly observed in medial, superior, and posterior directions. HCOR changes are influenced by surgical approach, potentially secondary to patient positioning, with greater posterior HCOR displacement observed in anterior cases. Surgeons should be aware of these factors, particularly in cases with deficient or reduced posterior column bone stock.

Pre-operative planning in THA. Part III: do implant size prediction and offset restoration influence functional outcomes after THA?

INTRODUCTION

Few studies evaluated clinical benefits of pre-operative templating in total hip arthroplasty (THA). We investigated whether mismatch between planned and real implant sizes and medio-lateral offsets compromises THA outcomes.

MATERIALS AND METHODS

We reviewed records of 184 primary THAs with pre-operative CT scans used for templating. Acetabular offset (AO), femoral offset (FO) and global offset (GO) were measured on pre-operative CT scans, during acetate templating, and post-operative antero-posterior radiographs. Multivariable analyses were performed to determine if Forgotten Joint Score (FJS) and Oxford Hip Score (OHS) at > 2 years were associated with differences between post-operative and planned parameters.

RESULTS

The FJS and OHS were not influenced by mismatch of component sizes nor of FO and GO. The FJS was better when the post-operative AO was greater than planned (p = 0.050). The FJS differed among arthritic types (p = 0.015). Multivariable analyses confirmed that older patients had better OHS (beta - 0.16; p = 0.033) and FJS (beta 0.74; p = 0.002), medialized hips had worse FJS (beta - 20.1; p = 0.041) and hips with greater AO than planned had better FJS (beta 1.71; p = 0.024) CONCLUSIONS: Implanting a component of different size than planned did not compromise THA outcomes, but medialized hips had worse scores, and conservative acetabular reaming improved scores.

Characteristics of radiographic morphometries of the lower leg in subjects with progression of knee osteoarthritis in the TOEI cohort

BACKGROUND

Knee osteoarthritis is one of the most common orthopedic diseases. However, few studies have reported the morphometric characteristics of the lower leg related to the progression of knee osteoarthritis in regional populations. This study aimed to determine the radiographic morphometries of the lower leg in subjects who showed progression of osteoarthritis of the knee in the TOEI cohort.

METHODS

Data were collected from the TOEI study cohort, during the period from 2014 to 2016, to assess osteoarthritis of the knee and radiographic morphometries of the lower leg. The joints were divided into three groups according to osteoarthritis progression over 2 years. There were 323 legs of females and 163 legs of males. Knees which did not exhibit osteoarthritis were in group 1; knees with osteoarthritis that remained stable for 2 years were in group 2; knees that worsened osteoarthritis over 2 years were in group 3. Morphometric parameters in the lower leg were measured by radiographs taken in 2014.

RESULTS

In female subjects, group 2 had higher age, lower lever arm ratio and lower hip-knee-ankle angle, and higher height of the hip center compared with group (1). Group 3 had higher age compared with group 1 and lower height of the hip center compared with group (2). In male subjects, group 2 had lower height of the hip center and lower hip-knee-ankle angle compared with group 1. Group 3 had higher patellar shift index compared with group 1, higher height of the hip center and higher femoral neck length compared with group 2.

CONCLUSIONS

Higher age was the risk of osteoarthritis progression of the knee in female subjects but not significant risk in male subjects. Hip morphometries such as height of the hip center and femoral neck length in which showed a sex difference might be associated with the progression of knee osteoarthritis.

Three-dimensional technology assisted trabecular metal cup and augments positioning in revision total hip arthroplasty with complex acetabular defects

BACKGROUND

Revision total hip arthroplasty (THA) with large acetabular defect remains a challenge. Though trabecular metal (TM) cup and augments have been introduced in defect reconstruction with good result, the accurate positioning of implant is important to avoid complications. Therefore, we aimed to evaluate the usefulness of three-dimensional (3D) simulation and 3D model in assisting implant positioning during complex revision THA.

METHODS

Sixteen patients (18 hips) who underwent revision THA with a Paprosky type III acetabular defect were analyzed retrospectively. Placement of acetabular cup and TM augments was simulated with 3D simulation software and 3D model preoperatively. Cup anteversion, abduction angle, and hip center were measured in each case preoperatively and postoperatively. Primary outcome was the percentage of outliers according to Lewinnek safe zone and Harris hip score (HHS). Secondary outcome was the correlation between the 3D planned and the postoperative value.

RESULTS

The percentage of outliers was significantly corrected from 77.78% (14/18) preoperatively to 38.88% (7/18) postoperatively (p = 0.04). There was a significant correlation between mean planned cup anteversion and postoperative value (13.39 vs 11.99, r = 0.894; p < 0.001). There was a significant correlation between mean planned abduction and postoperative value (42.67 vs 44.91, r = 0.921, p < 0.001). The number of planned and used augments was the same in all the cases. In 15 cases (83.33%), the size of planned and used TM augments was the same. The HHS was significantly improved at final follow-up (80.94 vs 27.50, p < 0.001). No cases presented dislocation or radiological signs of loosening.

CONCLUSION

Preoperative 3D simulation and model were considered the useful method to assist implant positioning in revision THA with complex acetabular defect, with moderate to high accuracy and satisfied clinical outcome.

Bilateral High Hip Center Provides Gait Parameters Similar to Anatomical Reconstruction: A Gait Analysis Study in Hip Replacement Patients With Bilateral Developmental Dysplasia

BACKGROUND

Total hip arthroplasty in severe dysplasia is challenging due to diminished periacetabular bone stock and the highly placed femoral head. Although anatomical reconstruction of the hip, with required interventions such as subtrochanteric osteotomy and graft usage, is the main aim of the procedure, good long-term clinical outcomes of the high hip center technique have also been reported. Information regarding the effect of hip center placement on gait characteristics is limited; therefore, the aim of this study is to analyze the differences in gait parameters between the high hip center technique and anatomical reconstruction of the hip.

METHODS

Twenty patients (40 hips) with bilateral Crowe type III-IV developmental dysplasia of the hip who underwent bilateral total hip arthroplasty and completed at least 2 years of follow-up were included. Group 1 comprised 10 patients (20 hips) who underwent anatomical hip center reconstruction, while group 2 comprised 10 patients (20 hips) who underwent high hip center reconstruction. The gait characteristics of patients were examined through markers placed in certain anatomical regions, the cameras placed around, and the force plates embedded in the walking platform.

RESULTS

There was no significant difference in the gait characteristics according to the location of the hip rotation center. The mean temporospatial, kinematic, and kinetic values were similar between the groups. The most prominent difference was in the peak dynamic hip extension, which was lower in group 2 (-9.71° ± 7.46°) compared to group 1 (-6.80° ± 11.44°), although it was not statistically significant (P = .09).

CONCLUSION

The bilateral high hip center technique can provide similar gait characteristics as anatomical reconstruction and may be preferred in particularly difficult cases based on the surgeon's decision.

Effect of placement of acetabular prosthesis on hip joint function after THA

The good recovery of hip function after THA depends on reconstruction of acetabular prosthesis accurately. So we investigated the effect of acetabular prosthesis placement on hip joint function after THA and analyzed the clinical data of 432 patients with unilateral THA retrospectively . The patients were followed-up to evaluate the Harris score and hip range of motion (ROM). The hip ROM, the Harris score and the good rate of Harris score were compared between different groups. Comparison of the good rate of Harris score showed that 85%∼100% group of the rotation center horizontal position ratio was higher than >100% group; 80%∼120% group of the rotation center vertical position ratio was higher than >160% group; and the 90%∼110% group and 110%∼130% group of femoral offset ratio were higher than 90% and >130% groups. Comparison of Harris score showed that 85%∼100% and 70%∼85% groups of rotation center horizontal position ratio were higher than 70% and >100% groups; 80%∼120% group of rotation center vertical position ratio was the highest; and 90%∼110% group and 110%∼130% group of femoral offset ratio were higher than >130% and 90% groups. Comparison of hip ROM showed that 85%∼100% and 70%∼85% groups of the rotation center horizontal position ratio were higher than 70% and >100% groups; 80%∼120% group of the rotation center vertical position ratio was the highest; and hip ROM from high to low are 90%∼110%, 110%∼130%, >130% and 90% groups of femoral offset ratio. These findings indicated that during the early follow-up period of THA, if the horizontal position of femoral head rotation center was reconstructed in 0.85 to 1 times of healthy side when compared with reconstruction >1 times of the healthy side and if the vertical position of femoral head rotation center was reconstructed in 0.8 to 1.2 times of the healthy side when compared with reconstruction in >1.6 times of the healthy side, better hip function recovery and optimal hip ROM were obtained. The optimal reconstruction range of femoral offset is 0.9 to 1.3 times of the healthy side.

High Hip Center Reduces the Dynamic Hip Range of Motion and Increases the Hip Load: A Gait Analysis Study in Hip Arthroplasty Patients With Unilateral Developmental Dysplasia

BACKGROUND

Long-term favorable clinical outcomes of anatomical or high hip center techniques in total hip arthroplasty (THA) are reported in patients with developmental dysplasia of the hip (DDH). However, there is little information about the effect of the hip center location on gait characteristics. The purpose of this study was to compare these surgical techniques with gait analysis, analyze the effect of the hip rotation center location on gait parameters, and discuss the possible problems that may arise.

METHODS

A total of 40 patients who underwent THA due to unilateral coxarthrosis secondary to Crowe type III-IV DDH and completed 5 years of follow-up were included in the study. Group 1 included 20 patients who underwent anatomical hip center reconstruction, while group 2 included 20 patients who underwent high hip center reconstruction. Gait analysis was performed, and the groups were compared according to the gait characteristics.

RESULTS

The mean temporospatial values were similar between the groups. The extension of the operated side was significantly lower in group 2 (-9.11 ± 8.92) than in group 1 (-1.87 ± 11.51) (P = .04). The mean longitudinal hip joint force was found to be significantly higher in group 2 (8.92 N/kg ± 0.54) than in group 1 (8.16 N/kg ± 0.66) (P = .04). The high hip center technique has been shown to increase the load on the hip and restrict the dynamic range of motion.

CONCLUSION

The high hip center technique can decrease the survival of the implant and increase the fall risk as it increases the load on the hip and reduces the dynamic range of motion. The hip center should be reconstructed anatomically when possible in DDH patients who undergo unilateral THA.

Restoring femoral offset and leg length; the potential of a short curved stem in total hip arthroplasty

Background

Total hip arthroplasty (THA) is a very successful procedure in orthopedics. Still polyethylene wear and gait deficits are limiting the clinical success.It is important to reconstruct leg length (LL) and femoral offset (FO) anatomically in order to have the best possible result of a THA. Gait deficits can arise due to leg length discrepancy as well as changes in the abductor moment arm. In THA, LL and FO are strongly determined by the orientation, size and geometry of the femoral stem.

Methods

This radio-anatomical study used the data of a prospective cases series of 112 patients who underwent 126 primary THAs and had completed a 1-year follow-up examination. FO and LL were compared between the conventional straight stem in vivo and a computed simulated implantation of a short curved stem, using the pre- and postoperative pelvic radiographs of the same patients.

Results

In this simulation of the short curved stem statistically significantly restored native FO (p = 0.010) and LL (p = 0.000) better, compared to the conventional straight stem.

Conclusions

Thus, the short curved stem restores FO and LL better, and could potentially prevent gait deficits.

Reconstruction of acetabular defects with porous tantalum shells and augments in revision total hip arthroplasty at ten-year follow-up

Aims

The use of trabecular metal (TM) shells supported by augments has provided good mid-term results after revision total hip arthroplasty (THA) in patients with a bony defect of the acetabulum. The aim of this study was to assess the long-term implant survivorship and radiological and clinical outcomes after acetabular revision using this technique.

Patients and Methods

Between 2006 and 2010, 60 patients (62 hips) underwent acetabular revision using a combination of a TM shell and augment. A total of 51 patients (53 hips) had complete follow-up at a minimum of seven years and were included in the study. Of these patients, 15 were men (29.4%) and 36 were women (70.6%). Their mean age at the time of revision THA was 64.6 years (28 to 85). Three patients (5.2%) had a Paprosky IIA defect, 13 (24.5%) had a type IIB defect, six (11.3%) had a type IIC defect, 22 (41.5%) had a type IIIA defect, and nine (17%) had a type IIIB defect. Five patients (9.4%) also had pelvic discontinuity.

Results

The overall survival of the acetabular component at a mean of ten years postoperatively was 92.5%. Three hips (5.6%) required further revision due to aseptic loosening, and one (1.9%) required revision for infection. Three hips with aseptic loosening failed, due to insufficient screw fixation of the shell in two and pelvic discontinuity in one. The mean Harris Hip Score improved significantly from 55 (35 to 68) preoperatively to 81 points (68 to 99) at the latest follow-up (p < 0.001).

Conclusion

The reconstruction of acetabular defects with TM shells and augments showed excellent long-term results. Supplementary screw fixation of the shell should be performed in every patient. Alternative techniques should be considered to address pelvic disconinuity. Cite this article: Bone Joint J 2019;101-B:311–316.

The influence of cavity preparation and press-fit cup implantation on restoring the hip rotation center

BACKGROUND

Reaming of the acetabular cavity and cup implantation directly influence the hip rotation center and contact area between implant and bone. Previous studies have reported on an altered rotation center after total hip arthroplasty, but have not studied the influence of reaming and cup implantation separately. Aim of this study was therefore to analyze the individual influence of acetabular reaming and subsequent cup implantation on the rotation center and how this influences the contact conditions at the bone-implant interface.

METHODS

Acetabular press-fit cups were implanted into the left and right hips of three full cadavers (n = 6). CT scans were performed to calculate the change in hip rotation center after reaming and prior to liner insertion. 3D models of the cups were used to determine the polar gap, the contact conditions and the effective press-fit.

FINDINGS

Reaming the acetabular cavity shifted the rotation center medially (median 5.8 mm, range 4.8-9.1), superiorly (5.3 mm, 3.0-7.0) and posteriorly (2.9 mm, 1.0-5.3). With cup implantation, the rotation center shifted back towards the native position, but no full restoration was observed. The degree of shift increased with the size of polar gap (r_s = 0.829, P = .042), which inversely reduced the contact area (r_s = 0.886, P = .019).

INTERPRETATION

This study reveals that the dominant factor in hip rotation center restoration is the reaming process, while the cup implantation for a given nominal press-fit has only a small influence. Increasing the press-fit would improve the restoration but bares the danger of insufficient bone coverage and periprosthetic fractures due to the high forces needed.

The Utilization of Metal Augments Allows Better Biomechanical Reconstruction of the Hip in Revision Total Hip Arthroplasty With Severe Acetabular Defects: A Comparative Study

BACKGROUND

Reconstructing the normal hip biomechanics is important for a successful revision total hip arthroplasty (THA). Little is known about whether using metal augments in revision THA is biomechanically superior to traditional techniques.

METHODS

A retrospective review was conducted on 74 consecutive THAs revised using metal augments with a cementless hemispherical cup and 77 consecutive THAs revised using the jumbo cup, all with a minimum 2-year follow-up. Biomechanical parameters were measured before and immediately after the revision. Radiological and clinical outcomes at follow-ups were also evaluated.

RESULTS

The metal augment group had a reconstructed center of rotation (COR) that was 6.5 mm closer to the anatomic COR in height (P < .001), had 3.6 m smaller cup size (P < .001), and had 5.7 mm less head-cup difference (P < .001). Moreover, there was a reconstructed COR that was much closer to the anatomic COR (vertical distance: 1.8 vs 14.1 mm, P < .001; horizontal distance: -2.1 vs 7.9 mm, P = .013), had 4.1 mm greater femoral offset (P = .006), and had 8 mm less leg length discrepancy (P = .035) in the subgroup of Paprosky type III bone defects when compared to the jumbo cup group. All cup-augment constructs were radiologically stable with a higher mean postoperative Harris Hip Score (P = .012). One jumbo cup was radiologically unstable.

CONCLUSION

In revision THA, utilizing metal augments helps to restore the COR position more precisely, avoid using a larger cup, reduce head-cup difference, rebuild femoral offset, and decrease leg length discrepancy, particularly with Paprosky type III bone defects. Moreover, it provides satisfactory radiological and clinical outcomes in the short term.

Is a short stem suitable for patients with hip dysplasia? A report on technical problems encountered during femoral reconstruction

INTRODUCTION

A wide variety of stems have been used for the treatment of osteoarthritis secondary to advanced hip dysplasia. Since evidence for using short stems in dysplastic hips is limited, we planned to analyse the technical problems encountered when reconstructing the proximal femur of patients with osteoarthritis secondary to congenital dysplasia of the hip treated with total hip arthroplasty (THA) using a type 2B short stem.

METHODS

We prospectively analysed 17 patients (22 hips) treated with primary THA performed with a single-branded short uncemented stem with metaphyseal fixation (MiniHip™; Corin). We excluded cases in which other type of stems were used, or in which retrospective data was only available. Mean follow-up was 41.22 months (minimum 24). We analysed clinical outcome using the modified Harris Hip Score (mHHS) and pain using the visual analogue scale (VAS). Radiographs were examined in order to determine causes of complications and revision surgery.

RESULTS

All patients showed statistically significant improvement when preoperative and postoperative values for mHHS (54.19 vs. 94.57; p = 0.0001) and for pain VAS (8.71 vs. 0.71; p = 0.0003) were compared. No cases of thigh pain, instability or infection were found. 1 case of acetabular cup loosening and 1 case of periprosthetic fracture were diagnosed at 8 months and 45 days, respectively. Overall survival was 84.7% at 5 years (CI 95%, 64.4-105.3) with revision for any reason as an end point. When stem performance was separately evaluated, it showed a survival rate of 100% at 5 years with revision for aseptic loosening as an end point.

CONCLUSIONS

THA with a type 2B short stem for the treatment of dysplastic osteoarthritis showed very few technical intraoperative problems, being a useful alternative for femoral reconstruction.

The Acetabular Fossa May Not Be Located at the True Center of the Acetabulum: A Detailed Analysis Using Preoperative CT Images

BACKGROUND

The acetabular fossa is thought to be located in the center of the acetabulum, and acetabular reaming in total hip arthroplasty is conventionally performed in the center of the fossa. However, the actual location of the fossa and the influence that hypoplasia or deformity may have on the position of the fossa are unknown. We hypothesized that the fossa is located in the center of the acetabulum, regardless of hypoplasia or deformity.

METHODS

Fifty patients with normal hips (normal hip group), 50 patients with dysplasia who underwent rotational acetabular osteotomy (dysplastic hip group), and 46 patients with osteoarthritis who underwent total hip arthroplasty (osteoarthritic hip group) were evaluated by computed tomography (CT) imaging. On the horizontal plane that passes through the center of the femoral head, the center line of the acetabulum was defined as the perpendicular bisector of the anterior and posterior rims of the acetabulum. The angle and distance of the center of the acetabular fossa in relation to the center line of the acetabulum were evaluated; furthermore, the center position of the fossa from the anterior margin of the acetabulum was calculated as a ratio relative to acetabular size. A 1-way analysis of variance was performed to compare measurements among the 3 groups.

RESULTS

The center of the acetabular fossa was positioned anteriorly to the center line of the acetabulum in all 3 groups. The mean center angle of the acetabular fossa was 14.0° ± 3.8°, 15.2° ± 5.6°, and 14.9° ± 5.5° in the normal, dysplastic, and osteoarthritic hip groups, respectively (p = 0.33). The mean center distance of the acetabular fossa was 5.6 ± 1.8, 5.8 ± 2.3, and 6.1 ± 2.2 mm, respectively (p = 0.55). The mean center position of the acetabular fossa was 38.8% ± 3.3%, 38.5% ± 4.2%, and 38.3% ± 3.9%, respectively (p = 0.71).

CONCLUSIONS

The center of the acetabular fossa is positioned anteriorly to the center of the acetabulum, and the positioning is affected by neither dysplasia nor osteoarthritis. The preconception that the center of the acetabulum corresponds to the center of the acetabular fossa may risk eccentric reaming, possibly damaging the anterior wall.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Radiographic evaluation of 19 patients with Paprosky 3A and 3B submitted to acetabular review with trabecular metal wedge

Objective

This study is aimed at evaluating the fixation of trabecular metal wedges in patients who underwent revision of total hip arthroplasty with large acetabular bone defects.

Methods

The radiographs of 19 patients (21 hips), who underwent revision of total hip arthroplasty using trabecular metal wedges from September 2010 to December 2014 were evaluated. This study included only cases of Paprosky 3A and 3B. Preoperative and postoperative images were analyzed. Non-fixation of the implant was defined by the presence of angular variation of the component higher 10 degrees or displacement greater than 6 mm. Patients with follow-up times of less than 24 months or who did not attend the last two appointments were excluded from the study.

Results

The mean follow-up time was 39.4 months (25–61). Fixation was achieved in all cases despite its complexity. There was only one case of dislocation that was treated with open reduction. One case developed infection, and was surgically approached on two occasions, with extensive debridement and intravenous antibiotics following protocol, with good evolution.

Conclusion

The implanted trabecular metal wedges showed excellent results in the short- and medium-term and may represent another option in the reconstruction of large acetabular defects, sometimes replacing bone reconstruction that uses bone tissue banks or autologous graft.

Lateral trochanteric pain following total hip arthroplasty: radiographic assessment of altered biomechanics as a potential aetiology

INTRODUCTION

Lateral trochanteric pain (LTP) complicates up to 17% of cases of total hip arthroplasty (THA). Studies have refuted underlying trochanteric bursitis. Restoration of the femoral offset and reproduction of the natural femoral centre of rotation are important in successful arthroplasty. LTP is believed to be associated with their alteration.

AIM

The aim of our study was to evaluate the effect of femoral offset and centre of rotation on the incidence of LTP post-THA.

METHODS

A retrospective case control study was developed from 158 patients who underwent a THA over a two-year period to form two patient cohorts. Twenty-nine patients diagnosed with LTP were matched with 110 control subjects. The direct lateral approach was used in all cases. Anterior-posterior pelvic radiographs before and after surgery were compared to assess the femoral, cup and global offsets and limb length discrepancies between the two groups. Statistical analyses were performed using the Mann-Whitney U test and independent samples t test.

RESULTS

Twenty-nine diagnosed with post-operative LTP. Sixty-two percent of symptomatic patients were female (p = 0.13). The median ages were 74.33 (symptomatic) and 70.71 (control) (p = 0.11). The differences (pre-post) of the femoral (p = 0.17), cup (p = 0.5) and global offsets (p = 0.99) and mean of limb length discrepancy (LLD) (p = 0.83) were not significant between the two groups.

CONCLUSION

No relationship was found between LTP and femoral offset or femoral centre of rotation. Disruption of the soft tissues during a lateral approach with resultant abductor tear, tendon defects and tendinitis might play a role in LTP and explain the apparent efficacy of corticosteroid injections.

Level of surgical experience is associated with change in hip center of rotation following cementless total hip arthroplasty: A radiographic assessment

Objectives

After total hip arthroplasty (THA), restoration of hip center of rotation (COR) is essential to ensure stability of the prosthetic hip and longevity of the prosthesis. Our aim was to determine whether, and how, the COR changed postoperatively compared to the native COR following implantation of a cementless acetabular component in anatomical position and to compare the accuracy of cup placement between two surgeons with different levels of surgical experience.

Materials and methods

We evaluated 145 patients (145 hips) who underwent unilateral primary THA, who had no distorted acetabulum on the affected hip and a normal contralateral hip. Hip reconstruction was radiologically and clinically assessed at a minimum 2-year follow-up. Perioperative change in COR, initial cup position, offset, leg-length discrepancy (LLD), radiographic cup orientation, Harris Hip Score (HHS), component loosening, and dislocations were compared between the highly experienced surgeon and less-experienced surgeon groups.

Results

The COR was significantly displaced in the superior and medial directions postoperatively. Significant differences were identified in the vertical COR change, initial cup position, LLD, cup inclination, and cups within safe zones, but not in the horizontal COR change, offset parameters, cup anteversion, or HHS. There were no radiographic evidence of component loosening in both groups, but three dislocations (7%) only in the group operated on by the less-experienced surgeon (p = 0.027).

Conclusions

We found that the postoperative COR tended to be displaced in the superior and medial directions, and that the level of surgical experience strongly affected the accuracy and consistency of cup placement, particularly in COR position and cup inclination.

Effects of perioperative factors and hip geometry on hip abductor muscle strength during the first 6 months after anterolateral total hip arthroplasty

[Purpose] The importance and effect of hip joint geometry on hip abductor muscle strength are well known. In addition, other perioperative factors are also known to affect hip abductor muscle strength. This study examined the relative importance of factors affecting hip abductor muscle strength after total hip arthroplasty. [Subjects and Methods] The subjects were 97 females with osteoarthritis scheduled for primary unilateral THA. The following variables were assessed preoperatively and 2 and 6 months after surgery: isometric hip abductor strength, radiographic analysis (Crowe class, postoperative femoral offset (FO)), Frenchay Activities Index, compliance rate with home exercise, Japanese Orthopaedic Association Hip-Disease Evaluation Questionnaire (JHEQ), and demographic data. Factors related to isometric hip abductor muscle strength 2 and 6 months after surgery were examined. [Results] Significant factors related to isometric hip abductor muscle strength at 2 and 6 months after surgery were, in extraction order: 1. isometric hip abductor muscle strength in the preoperative period; 2. BMI; and 3. the JHEQ mental score at 2 and 6 months after surgery. [Conclusion] Preoperative factors and postoperative mental status were related to postoperative isometric hip abductor strength. FO was not extracted as a significant factor related to postoperative isomeric hip abductor strength.

Use of Oversized Highly Porous Cups in Acetabular Revision

This study assessed the efficacy of highly porous cups in revision total hip arthroplasty for Paprosky types II and III acetabular bone loss. The authors identified 33 acetabular revisions in 29 patients from a prospective database (66% type III, 7 with pelvic dissociation). Initial stability was achieved with interference fit between the anterior inferior iliac spine, pubis, and ischium with cups that were 2 to 4 mm larger than the reamed acetabulum and augmented with multiple screw fixations without allograft or wedges. At mean follow-up of 6 years (range, 2.7-7.7 years) after revision surgery, no dislocation, infection, or reoperation was noted. Mean satisfaction score was 6±3.2. Mean anteversion and abduction angles were 43°±4.6° and 21.5°±4.4°, respectively. Complications included limp in 13% of patients, wound issues in 10%, and heterotopic ossification in 17%. Osteointegration was seen in all cups, without any migration. Mean overall osteointegration, based on the average percentage of the 3 zones in both views, was 55%±21% (range, 25%-95%). The most osteointegration was seen in zone I (superior) and zone VI (posterior), and the least osseointegration was seen in zone II (medial) and zone IV (anterior). This method can provide reproducible results in acetabular revision arthroplasty.

A radiological study of the true anatomical position of the acetabulum in Japanese women

There is sometimes uncertainty concerning the correct socket position prior to total hip arthroplasty (THA). We conducted a study to determine the hip centre in Japanese women in order to define the true anatomical position of the acetabulum. The study involved 200 consecutive female patients in whom the contralateral hip joint was normal or was prearthritic and who underwent unilateral THA. The 'normal' group comprised 100 hip joints with no acetabular hip dysplasia, and the prearthritis group comprised 100 hip joints with Crowe type I dysplasia. The length of a perpendicular line drawn under the teardrop (interteardrop line) connecting both inferior edges of the teardrop with the centre of the femoral head was recorded as the vertical distance, and the distance from the intersection of the perpendicular line and interteardrop line up to the teardrop was recorded as the horizontal distance. We measured these distances on the femoral head of the side that did not undergo THA. The mean vertical distances in the 'normal' and prearthritis groups were 14.6 ± 2.8 mm and 16.8 ± 2.7 mm, respectively, and the mean horizontal distances were 30.2 ± 2.8 mm and 32.5 ± 2.7 mm, respectively. We therefore determined the mean centre of the hips to lie at a vertical distance of 11 to 22 mm and a horizontal distance of 27 to 38 mm. These values can serve as a useful index for socket positioning in THA.

Changes of center of rotation and femoral offset in total hip arthroplasty

BACKGROUND

It is a challenge to reconstruct the center of rotation (COR) and femoroacetabular offset anatomically in total hip arthroplasty (THA). We addressed the controversy how we manage to preserve the COR and femoroacetabular offset with an uncemented total hip prosthesis implanted with free hand technique.

METHODS

We analyzed a prospective series of 73 patients who underwent primary THA. The series was composed of 40 females and 33 males, mean age 64 years (range, 35-90 years). The reasons for THA were primary osteoarthritis (n=63) and developmental dysplasia of the hip (n=10). Pre- and postoperative X-rays were done in a standardized format for anterior-posterior (AP) radiographs of the pelvis, and digitalized measurements were done using SectraTM. We compared preoperative measurements with the final outcome to determine changes in COR and femoral offset.

RESULTS

We found that 40 patients had their COR and 34 patients had their femoral offset preserved within preoperative 5.0 mm limits. Twenty-three patients had both their values of COR and femoral offset preserved within 5.0 mm limits. While a significant correlation was found between changes of femoral and global offset (r=0.786, P<0.001), there were no correlation between changes of acetabular and femoral offset (r=-0.027, P=0.822).

CONCLUSIONS

Using an uncemented THA and free hand technique, there is a fair reproducibility of anatomy. The variations were mostly minor, but our results indicate a potential for better restoring the location of COR and femoral offset when planning and implanting an uncemented THA.

Comparison of Head Center Position and Screw Fixation Options Between a Jumbo Cup and an Offset Center of Rotation Cup in Revision Total Hip Arthroplasty: A Computer Simulation Study

Jumbo acetabular cups are commonly used in revision total hip arthroplasty (THA). A straightforward reaming technique is used which is similar to primary THA. However, jumbo cups may also be associated with hip center elevation, limited screw fixation options, and anterior soft tissue impingement. A partially truncated hemispherical shell was designed with an offset center of rotation, thick superior rim, and beveled anterior and superior rims as an alternative to a conventional jumbo cup. A three dimensional computer simulation was used to assess head center position and safe screw trajectories. Results of this in vitro study indicate that a modified hemispherical implant geometry can reduce head center elevation while permitting favorable screw fixation trajectories into the pelvis in comparison to a conventional jumbo cup.