Dual-mobility bearings: a review of the literature

Does-dual mobility still offer improved stability in smaller cup sizes? A computer modelling comparison of stability with 22-mm versus 28-mm inner heads in dual-mobility versus single-bearing constructs

PURPOSE

Dislocation remains 1 of the leading causes of revision after primary total hip arthroplasty (THA) and there is clear evidence the dual-mobility (DM) is used more frequently to minimise this. But in smaller cups, whether the use of DM with smaller 22-mm heads imparts any increased stability compared to standard bearing is unknown; especially when those smaller cups now allow for large single-bearing (SB) heads.

METHODS

3 primary cup sizes (48 mm, 50 mm, 52 mm) were chosen a priori for modelling. Head sizes trialled for the standard bearing (SB) constructs group were 28-0 mm, 32-0 mm and 36-0 mm against neutral polyethylene liners. In the modular sub-hemispheric DM constructs the inner head sizes for the DM constructs were altered where appropriate (22-0 mm vs. 28-0 mm). Cup position, stem offset, and stem size were standardised.

RESULTS

Both DM constructs outperformed all SB constructs because of a statistically significant jump distance increase (p < 0.001). However, there was no difference in range of motion (ROM) or jump distances between the 22-mm and 28-mm DM inner heads.The ROM angle before impingement between the DM (with 22-mm or 28-mm heads) and SB (with different head sizes where appropriate) showed no statistically significant difference. However, DM constructs presented significantly larger jump distances than SB constructs for both provocative dislocation tests across all 3 cup sizes.Of interest, for 50-mm and 52-mm cup sizes (for which this particular DM construct design can accommodate both 22-mm and 28-mm inner heads), there were no differences in ROM or jump distance between 22-mm versus 28-mm inner heads.

CONCLUSIONS

In this computer-modelling study, DM constructs are advantageous over SB constructs for improving jump distances in clinically provocative positions, but not range of motion angles. Inner head diameter of DM has no effect on stability.

Comparison of Outcomes in Dual-Mobility Versus Fixed-Bearing Implants in Primary Total Hip Arthroplasty: A Systematic Review and Meta-Analysis

Total hip arthroplasty (THA) is often regarded as one of the most successful surgical techniques developed in the twenty-first century. However, it is associated with complications such as prosthetic instability, dislocations, or infections. Dual-mobility (DM) implants have been developed with the goal of reducing the incidence of dislocations by increasing the femoral head-neck ratio, maximising hip stability, and improving the range of motion (ROM) before impingement and dislocation. This systematic review aims to comprehensively compare the safety and efficacy of DM versus fixed-bearing (FB) implants in primary THA patients. A comprehensive search strategy of PubMed, Embase, Scopus, and Web of Science Core Collection databases was executed to identify pertinent literature comparing DM and FB implants in THAs. Eligible studies underwent independent screening, and data were systematically extracted. The analysis employed pooled risk ratios (RR) for dichotomous outcomes and mean differences (MD) for continuous variables, each accompanied by their respective 95% confidence intervals (CI). Our systematic review and meta-analysis included nine studies encompassing 22,277 patients. The DM group had a significantly reduced incidence of dislocations compared to the FB group (RR 0.25, 95%CI [0.13, 0.47]; p-value <0.0001) and a significantly shorter length of stay (MD -9.92, 95%CI [-15.53, -4.32]; p-value = 0.0005). The FB group, however, had a significantly shorter operative time compared to the DM group (MD 10.41, 95%CI [7.64, 13.17]; p-value < 0.00001). We did not identify any significant statistical differences between the DM and FB groups regarding patient-reported outcome measures, the incidence of all-cause readmissions, the incidence of peri-prosthetic fractures, the incidence of infections, or the incidence of groyne pain.

A Meta-Analysis to Evaluate Implant Survival and Benefits of the Use of Dual Mobility Constructs in Total Hip Replacement Following Hip Fracture

Total hip replacement (THR) is commonly performed to treat hip fractures. Dual-mobility constructs (DMCs) are increasingly used for this indication. The aim of this study was to use evidence synthesis techniques to estimate net all-cause construct survival for THR with DMC performed for hip fracture. Additionally, we aimed to investigate and describe differences in all-cause construct survival (if present) between THRs performed with DMC (DMC-THR) or with a conventional bearing construct following hip fracture. We performed a systematic review and meta-analysis of published studies (including joint registries), including DMC-THR for hip fracture which provided Kaplan-Meier (KM) survival estimates. The primary outcome was all-cause construct survival over time. The study was prospectively registered on PROSPERO (CRD42020173117). A total of 557 papers and 17 registry reports were identified. Six studies (four registry reports, one matched-pair cohort study utilising joint registry data, and one single-institution case series) met the inclusion criteria, including 17,370 DMC THRs and 167,377 conventional THRs. Five-year KM survival estimates (95% confidence intervals) were similar at 95.4% (94.9 to 95.8%) for DMC-THR and 96.2% (96.0 to 96.4%) for conventional THR. The relative risk of revision for DMC-THR at five years was 1.21 (1.05 to 1.41). These results suggest that DMC-THR has a lower all-cause survival than conventional THR following hip fracture. This analysis does not support the routine use of DMC-THR over conventional bearing THR.

Outcomes of Dual Mobility Bearings in Revision Total Hip Replacements

Background Dual mobility bearings have gained attention in the prevention of instability in revision total hip replacement. This study aimed to evaluate the use of dual mobility bearings in revision total hip replacement. The primary outcome was the rate of dislocation. Secondary outcomes included the rate of re-operation for any reason, surgical complications, serious medical adverse events, and 90-day mortality rate. Methods A single-centre case series of 55 consecutive operations in 49 patients who underwent revision total hip replacement using dual mobility bearings with a minimum follow-up of three months was studied.  Results Early dislocation occurred in one case (2%), and there were no intra-prosthetic dislocations at a mean follow-up of 16 months. The rate of re-operation for any reason was 6/55 (11%) cases, and the post-operative infection rate was 2/55 (4%) cases. Serious medical adverse events occurred in 2/55 (4%) cases. The 90-day mortality rate was 1/55 (2%) cases. Two cases (2%) had cup abduction or anteversion angles outside of the safe zones although there were no dislocations in these patients. Conclusion This case series demonstrates a low dislocation rate in the early post-operative period for dual mobility bearings in revision total hip replacement. Dual mobility bearings show promise as an early low dislocation implant in revision total hip replacement. It remains to be determined whether dual mobility bearings are low-wear implants in the long term.

Two-Year Outcomes of Novel Dual-Mobility Implant in Primary Total Hip Arthroplasty

Introduction

Dual-mobility (DM) implants for total hip arthroplasty (THA) have gained popularity due to their potential to reduce hip instability and dislocation events that may lead to revision surgery. These implants consist of a femoral head articulated within a polyethylene liner, which articulates within an outer acetabular shell, creating a dual-bearing surface. Our study aimed to report our observations on the survivorship of a novel DM implant for primary total hip arthroplasty at two years.

Methods

We conducted a retrospective, multicenter study to assess the clinical outcomes of patients undergoing a THA with a novel DM implant (OR3O acetabular system™, Smith & Nephew, Inc., Memphis, TN) from January 2020 to September 2021. Patient demographics, surgical information, and survivorship data were collected from medical records for patients with a minimum of two years of follow-up. Primary outcomes included overall implant survivorship at two years as well as aseptic survivorship, revision rates of the DM acetabular shell, and average time to revision. Patient-reported outcomes were collected in the form of HOOS JR.

Results

A total of 250 hips in 245 patients had a minimum two-year follow-up. Primary osteoarthritis (80%) was the most common indication for index THA. The average aseptic survivorship of the DM acetabular components at two years for the cohort was 98.4% and survivorship of the acetabular implants overall was 97.6%. There were a total of four (1.6%) aseptic revisions of the DM acetabular component. Reasons for aseptic acetabular revision included one case of instability, one intraprosthetic dislocation, one periprosthetic acetabular fracture, and one malpositioned acetabular cup resulting in impingement. The mean time of follow-up was 893.9 days. Eighty-seven patients had preoperative and two-year HOOS JR available. HOOS JR improved by an average of 38.5 points.

Conclusion

This novel DM acetabular implant demonstrates excellent survivorship at two years follow-up with low rates of instability and intraprosthetic dislocation and no episodes of metal-on-metal corrosion. Use of the DM implant demonstrated clinically relevant improvements in patient-reported outcomes at two years.

The Practicality of the Robotic Total Hip Arthroplasty for the Treatment of Complex Bilateral Adult Hip Dysplasia. Technology Makes It Easy

Adult hip dysplasia provides many challenges for joint surgeons. Due to the abnormal bone morphology and altered biomechanics of the hip, surgeons must ensure accurate implant positioning to avoid postoperative complications. We present a 56-year-old female with a history of bilateral Legg-Calve-Perthes disease and subsequent dysplasia who underwent bilateral total hip arthroplasty using robotic navigation. We highlight the utility of robotic navigation in adult hip dysplasia to improve implant positioning and ensure optimal patient outcomes.

Selective Use of Dual-Mobility Did Not Significantly Reduce 90-Day Readmissions or Reoperations after Total Hip Arthroplasty

INTRODUCTION

Selective use of dual mobility (DM) implants in total hip arthroplasty (THA) patients at high dislocation risk has been proposed. However, evidence-based utilization thresholds have not been defined. We explored whether surgeon-specific rates of DM utilization correlate with rates of readmission and reoperation for dislocation.

METHODS

We retrospectively reviewed 14,818 primary THA procedures performed at a single institution between 2011 and 2021, including 14,310 FB and 508 DM implant constructs. Outcomes including 90-day readmissions and reoperations were compared between patients who had fixed-bearing (FB) and DM implants. Cases were then stratified into three groups based on the attending surgeon's rate of DM utilization (≤1, 1 to 10, or >10%) and outcomes were compared.

RESULTS

There were no differences in 90-day outcomes between FB and DM implant groups. Surgeon frequency of DM utilization ranged from 0 to 43%. There were 48 surgeons (73%) who used DM in ≤ 1% of cases, 11 (17%) in 1 to 10% of cases, and 7 (10%) in >10% of cases. The 90-day rates of readmission (7.3 vs 7.6 vs 7.2%, P=0.7) and reoperation (3.4 vs 3.9 vs 3.8%, P=0.3), as well as readmission for instability (0.5 vs 0.6 vs 0.8%, P=0.2) and reoperation for instability (0.5 vs 0.5 vs 0.8%, P=0.6), did not statistically differ between cohorts.

CONCLUSION

Selective DM utilization did not reduce 90-day readmissions or reoperations following primary THA. Other dislocation-mitigation strategies (i.e., surgical approach, computer navigation, robotic assistance, and large diameter fixed-bearings) may have masked any benefits of selective DM use.

Do Modular Dual Mobility Cups Offer a Reliable Benefit? Minimum 5-Year Follow-Up of 102 Cups

BACKGROUND

Among various options suggested to prevent hip instability after total hip replacement, the MDM-tritanium (modular dual mobility) cup features a cobalt-chrome liner (CoCr) positioned in a titanium acetabular shell and matched with a mobile insert in highly cross-linked annealed X3 polyethylene. The purpose of this study aimed to confirm whether there was no significant release of ions (Co and Cr) or higher occurrence of dislocation or even cases of aseptic loosening of the cementless shell with the use of MDM-tritanium cups at minimum of 5-year follow-up.

METHODS

The clinical study was carried out on a homogeneous consecutive and nonselective series with 102 MDM cups (98 patients) implanted in 2 centers. This MDM-tritanium cup had been systematically used for surgical revisions (70% of cases) or for patients with major hip dysplasia or in elderly patients with poor bone quality. A biological assessment of ion releases has been performed in a specific cohort of 39 cases that had an internal ceramic head.

RESULTS

None of the following complications was observed: no case of immunoallergic event, no aseptic loosening, and the dislocation rate was 4.9% involving only the difficult primary and revision cases. The clinical results were encouraging, with 89.7 points for Harris Hip Score, 41.16 points/48 for the OHS-12. The Agora Roentgenographic Assessment (ARA) radiologic score was graded "excellent" in 94.4%. The MDM-tritanium survivorship with revision for any cause in 102 cups at 7.95 years was 92.7%.

CONCLUSION

Based on the results of our first 102 cases, there were no immunoallergic complications-contrary to what was initially feared with the CoCr bearing-titanium pair-and no postoperative instability, including for complex primary and revisions total hip replacements.

LEVEL OF EVIDENCE

Individual Cohort Study: 2B.

The Incidence and Temporal Trends of Dislocation After the Use of Constrained Acetabular Components and Dual Mobility Implants in Primary Total Hip Replacements: A Systematic Review and Meta-Analysis of Longitudinal Observational Studies

BACKGROUND

Dislocation after a primary total hip replacement (pTHR) remains a common cause of treatment failure. Constrained acetabular components (CACs) and dual mobility implants (DMIs) may mitigate this in patients at high risk of dislocation or with significant intraoperative instability. This meta-analysis evaluated the incidence and temporal trends of dislocation after implantation with CACs and DMIs in pTHR.

METHODS

Longitudinal studies reporting dislocation after the use of CACs or DMIs in pTHR were sought from Medline and Embase to September 2020. Secondary outcomes included revision surgery for dislocation and for all causes.

RESULTS

A total of 46 studies (3 CAC and 43 DMI) comprising 582 CACs and 18,748 DMIs were included. The pooled incidence of dislocation was 1.08% (95% confidence interval [CI]: 0.00-3.72; range 0.27%-2.60%) over a weighted mean follow-up of 4.1 years for CACs, compared with 0.25% (95% CI: 0.08-0.46; range 0.00%-4.72%) over 6.2 years for DMIs. For DMIs, there was a temporal decline in dislocations from the 1980s onward, and dislocation rates remained low (<1%) until 15 years postoperatively. There were insufficient data for similar analysis of CACs. All studies were at high risk of bias. The incidence of revision for dislocation after CACs was 0.3% vs 0.1% for DMIs, and the incidence of revision for all causes after CACs was 4.8% vs 2.7% for DMIs.

CONCLUSION

DMIs demonstrated a lower incidence of dislocation compared with CACs; however, there was a relative absence of CACs used in the context of pTHR in the literature. Temporal trends in dislocation have improved over time for DMIs.

Is Dual Mobility Total Hip Arthroplasty Surgery More Aggressive than Hemiarthroplasty when Treating Femoral Neck Fracture in the Elderly? A Multicentric Retrospective Study on 302 Hips

Introduction

Bipolar hemiarthroplasty (BHA) and total hip arthroplasty (THA) are validated treatments for displaced femoral neck fractures (DFNFs). BHA seldomly needs conversion to THA, but the latter has higher dislocation rate in FNFs. Dual Mobility THA offers a reduced dislocation rate and eliminates the risk of conversion. This study looks for differences between BHA and DMTHA in terms of surgical time, blood loss and transfusion, dislocation rate, mortality, and thromboembolic events.

Material and Methods

All patients were ≥75yo. Recorded data included use of anticoagulant/antiplatelet drugs, ASA, operative time, intra-operative complications, pre/post-operative hemoglobin values, transfusions, hospitalization time, DVT/PE, glomerular filtration rate, Charlson Comorbidity Index (CCI), dislocation at 60 days, and mortality at 30 days and 6 months. A secondary analysis compared the subgroups in different age range (75–85 and ≥ 86yo).

Results

In the cohort of 302 DFNF (93 BHA and 209 DMTHA) differences in mean age, CCI, and ASA score were significant. Once divided by age, the subgroups resulted comparable in terms of age and CCI, with no significant difference. A significant difference in surgical times showed DMTHA being an average 12 minutes longer than BHA. Significant was the ΔHB in the DMTHA subgroup which resulted lower compared to the BHA one. Difference in mean number of post-operative transfusion were not statistically significant.

Conclusions

From our data, DMTHA did not lead to an increase in mortality, morbidity, bleeding, or dislocation rate when compared to BHA and could be considered as treatment of choice for DFNFs especially in healthy and active patients.

Effect of intraoperative treatment options on hip joint stability following total hip arthroplasty

Dislocation remains the leading indication for revision of total hip arthroplasty (THA). The objective of this study was to use a computational model to compare the overall resistance to both anterior and posterior dislocation for the available THA constructs commonly considered by surgeons attempting to produce a stable joint. Patient-specific musculoskeletal models of THA patients performing activities consistent with anterior and posterior dislocation were developed to calculate joint contact forces and joint positions used for simulations of dislocation in a finite element model of the implanted hip that included an experimentally calibrated hip capsule representation. Dislocations were then performed with consideration of offset using +5 and +9 offset, iteratively with three lipped liner variations in jump distance (10°, 15°, and 20° lips), a size 40 head, and a dual-mobility construct. Dislocation resistance was quantified as the moment required to dislocate the hip and the integral of the moment-flexion angle (dislocation energy). Increasing head diameter increased resistive moment on average for anterior and posterior dislocation by 22% relative to a neutral configuration. A lipped liner resulted in increases in the resistive moment to posterior dislocation of 9%, 19%, and 47% for 10°, 15°, and 20° lips, a sensitivity of approximately 2.8 Nm/mm of additional jump distance. A dual-mobility acetabular design resulted in an average 38% increase in resistive moment and 92% increase in dislocation energy for anterior and posterior dislocation. A quantitative understanding of tradeoffs in the dislocation risk inherent to THA construct options is valuable in supporting surgical decision making.

Dislocation of Total Hip Replacement in Femoral Neck Fracture: Do Surgical Approach and Dual Mobility Implant Matter?

INTRODUCTION

Total hip replacement (THR) in the neck of femur fracture in the elderly is associated with a higher risk of dislocation compared to hemiarthroplasty of hip or total hip replacement in the native hip. There is uncertainty regarding combining surgical approach, femoral head size, and the usage of single bearing or dual mobility to reduce the risk of dislocation. This study looks into the bearing of the prosthesis for posterior or lateral surgical hip approach as well as their head size to give a stable hip to these vulnerable groups of patients.

METHODS

Initial data were collected retrospectively from February 2017 till May 2019 from the electronic records database and clinical notes. Patients included in the study had a femoral neck fracture (age >60 years) who underwent a total hip replacement. Subsequent data were collected prospectively from June 2019 to July 2020.

RESULTS

High rate of dislocation was found with posterior approach and single bearing prosthesis. However, if dual mobility prosthesis was used while using the posterior approach the dislocation rate was very low. Also, with lateral approach and single bearing prosthesis using large femoral head size, the dislocation rate was negligible.

CONCLUSIONS

We recommend a dual mobility prosthesis for posterior approach THR and lateral approach with single-bearing hip replacement with large size femoral head. The dislocation rate is low using this principle irrespective of the surgical approach.

Acetabular complications are the most common cause for revision surgery following proximal femoral endoprosthetic replacement : what is the best bearing option in the primary and revision setting?

AIMS

Proximal femoral endoprosthetic replacements (PFEPRs) are the most common reconstruction option for osseous defects following primary and metastatic tumour resection. This study aimed to compare the rate of implant failure between PFEPRs with monopolar and bipolar hemiarthroplasties and acetabular arthroplasties, and determine the optimum articulation for revision PFEPRs.

METHODS

This is a retrospective review of 233 patients who underwent PFEPR. The mean age was 54.7 years (SD 18.2), and 99 (42.5%) were male. There were 90 patients with primary bone tumours (38.6%), 122 with metastatic bone disease (52.4%), and 21 with haematological malignancy (9.0%). A total of 128 patients had monopolar (54.9%), 74 had bipolar hemiarthroplasty heads (31.8%), and 31 underwent acetabular arthroplasty (13.3%).

RESULTS

At a mean 74.4 months follow-up, the overall revision rate was 15.0%. Primary malignancy (p < 0.001) and age < 50 years (p < 0.001) were risk factors for revision. The risks of death and implant failure were similar in patients with primary disease (p = 0.872), but the risk of death was significantly greater for patients who had metastatic bone disease (p < 0.001). Acetabular-related implant failures comprised 74.3% of revisions; however, no difference between hemiarthroplasty or arthroplasty groups (p = 0.209), or between monopolar or bipolar hemiarthroplasties (p = 0.307), was observed. There was greater radiological wear in patients with longer follow-up and primary bone malignancy. Re-revision rates following a revision PFEPR was 34.3%, with dual-mobility bearings having the lowest rate of instability and re-revision (15.4%).

CONCLUSION

Hemiarthroplasty and arthroplasty PFEPRs carry the same risk of revision in the medium term, and is primarily due to acetabular complications. There is no difference in revision rates or erosion between monopolar and bipolar hemiarthroplasties. The main causes of failure were acetabular wear in the hemiarthroplasty group and instability in the arthroplasty group. These risks should be balanced and patient prognosis considered when contemplating the bearing choice. Dual-mobility, constrained bearings, or large diameter heads (> 32 mm) are recommended in all revision PFEPRs. Cite this article: Bone Joint J 2021;103-B(10):1633-1640.

Intraoperative Fracture of a Dual Modular Delta Ceramic Femoral Head During Total Hip Arthroplasty: A Case Report

CASE

A 39-year-old man with cerebral palsy and hip dysplasia status post right Chiari osteotomy presented with right hip osteoarthritis in consultation for total hip arthroplasty (THA). During THA, a Delta ceramic head was misaligned on the taper, but this was obscured by an overlying dual modular polyethylene shell. When we attempted to tap the head onto the taper, fracture occurred requiring revision to a cobalt-chromium head due to slight taper damage.

CONCLUSION

To our knowledge, this is the first reported case of intraoperative fracture of a BIOLOX Delta dual modular head.

Novel Constrained Dual Mobility Hip Prosthesis to Combat Instability in Revision Total Hip Arthroplasty whilst Preserving Normal Function

We present the case of a male patient with sepsis and a chronic discharging sinus in a multirevised total hip replacement. Following extensive debridement, the reimplanted hip became unstable. With the patient's long-term desire to return to work and ride a bicycle with his children, the patient agreed to proceed with a novel, custom-designed, constrained dual mobility liner which allowed unrestricted movement. In 2017, the patient underwent revision surgery with this novel dual mobility constrained prosthesis. The patient was very quickly able to regain independence. After 16 years of unemployment, he managed to return to gainful employment as a cleaner rapidly regaining function as well as finally being able to ride a bike with his children for the first time.

Iatrogenic intraprosthetic dislocation after closed reduction of dual mobility total hip arthroplasty: Report of two cases

INTRODUCTION

Among hip arthroplasty, dual mobility aims to improve ROM and reduce dislocation rates, however this particular implant can fail in specific ways. Iatrogenic intraprosthetic dislocation (IPD) is a rare occurrence that can happen during closed reduction of a dislocated dual mobility total hip arthroplasty.

PRESENTATION OF CASE

#1 - A 34-year-old male who came to our attention with an undiagnosed IPD. He had experienced a classic dislocation 6 days earlier, which was treated with closed reduction. CT-scan confirmed decoupling of the metal head and PE liner. #2 - An 89-year-old male came to our attention for THA dislocation. During closed reduction manouvers he suffered IPD of the implant. Both patients were treated with revision surgery.

DISCUSSION

Despite being already reported in literature, IPD are still not well known to practitioners and sometimes overlooked even by orthopaedic specialists. Given the good results and diffusion of this kind of implant, iatrogenic IPD in the contest of a classic dislocation might become more frequent in the clinical practice.

CONCLUSION

When performing reduction maneuvers for a dislocated dual mobility total hip arthroplasty, X-rays must be carefully inspected for signs of IPD which, if undiagnosed, can lead to major implant damage and the need for extensive revision surgery.

Effects of Daily Activities and Position on Kinematics and Contact Mechanics of Dual Mobility Hip Implant

Dual mobility hip implants have been widely introduced to overcome dislocation in recent years. However, the potential influence of different gaits on kinematics and contact mechanics for dual mobility hip implants is still unclear. Furthermore, a large range of motion coupling with the implant position, especially high inclination or anteversion angle, may result in poor kinematics and contact mechanics. A previously developed dynamic finite element method was adopted in this study to examine the kinematics and corresponding stability of dual mobility hip implants under different gaits coupling with different inclinations or anteversion angles. The results showed only inner relative sliding under knee-bending for dual mobility hip implants under moderate inclination and anteversion angles, whereas an anteversion angle of 25° induced both impingement and consequent relative sliding of the outer articulation. However, the impingement (between the stem neck and the liner inner rim) indeed happened under stair-climbing and sitting-down/stand-up as well as combined movements when inclination and anteversion angles were set as 45° and 0°, respectively, and this finally led to relative sliding at the outer articulation. A high inclination angle did not worsen both the impingement and related outer sliding compared to modest inclination and anteversion angles of the liner, but a high anteversion angle prolonged the period of both the impingement and the outer relative sliding. The extreme motions and high anteversion angles are hardly inevitable, and they indeed lead to motions at both articulations for dual mobility hip implants.

Lack of early dislocation for dual mobility vs. fixed bearing total hip arthroplasty: A multi-center analysis of comparable cohorts

Background

Dislocation is a major cause of morbidity and revision surgery following total hip arthroplasty (THA). To address such issues, dual mobility (DM) bearings were introduced as a more stable alternative to fixed-bearing (FB) prostheses. As such, we compared DM and FB systems in a cohort study in terms of dislocations, readmissions, and revisions.

Methods

A 27 multi-center retrospective review was performed of 664 DM and 218 FB cases from the same manufacturer with mean follow-up of 2.09 years and 1.83 years, respectively. Patient reported outcome measures (PROMs) including Harris Hip Score (HHS), SF12, EQ5D, and Lower Extremity Activity Score (LEAS) were evaluated as well as dislocation rates, readmissions, and revisions rates. We also performed a survivorship analysis through Kaplan-Meier estimator. Students t-test was used for normally distributed continuous data and Fisher exact test (P < 0.05) was used for discrete data.

Results

There were 0 dislocations in the DM (0%) group and 2 dislocations in the FB (0.92%) group (p = 0.06). Latest follow up HHS revealed a significant difference between groups (91.44 DM and 87.81 FB; p = 0.006). In addition, there was significant difference between DM and FB on SF12 Physical Component Score (PCS) (46.83 and 44.55, respectively, p = 0.015). Also, readmission rates at 30, 60 and 90 days remained lower for DM than for FB at each time point (1.05% vs. 2.75%, 1.81% vs. 2.75%, and 1.81% vs. 2.75, respectively). Overall, DM had a lower revision rate at 1.51% compared to 2.29% for FB (p = 0.24). The revision breakdown for DM revealed 0 (0%) for both Anatomic Dual Mobility (ADM) and Modular Dual Mobility (MDM) due to the acetabular component.) There was a difference, 14 (87.5%) for ADM and 2 (12.5%) due to the femoral component. The survivorship analysis revealed no significance difference between DM and FB at 4 years (97.90% and 97.26%, respectively).

Conclusion

In comparison to patients who undergo FB THA, DM bearings have improved PROMs and a lower rate of dislocation, readmission, and revision.

Midterm Clinical and Radiographic Outcomes of a Contemporary Monoblock Dual-Mobility Cup in Uncemented Total Hip Arthroplasty

BACKGROUND

The efficacy of contemporary monoblock dual-mobility (DM) cups to prevent dislocations in total hip arthroplasty (THA) is well reported, but there is little published data on their mid- to long-term outcomes. The authors aimed at reporting the 10-year survival of a contemporary DM cup as well as its clinical and radiographic outcomes.

METHODS

From a retrospective consecutive multicentric series of 516 patients (541 hips) that received uncemented THA between June 2007 and June 2010, 6 patients (6 hips) had cup and stem revisions, 5 patients (5 hips) had isolated stem revision, and 2 patients (2 hips) had isolated insert revision. A total of 103 patients (111 hips) died with their original implants, and 41 patients (42 hips) were lost to follow-up. This left 358 patients (375 hips) for clinical assessment at a median follow-up of 8.7 years (range, 6.8-10.5 years), including 279 patients (290 hips) with postoperative radiographs. Implant survival was calculated using the Kaplan-Meier method, and multivariable analyses were performed to determine whether clinical outcomes are associated with patient or surgical factors.

RESULTS

The 10-year survival considering revision for aseptic loosening as end point was 100% for the cup and 99.2% for the stem. No dislocations were observed, and radiographic assessment revealed 1 acetabular granuloma (0.3%), but no radiolucencies nor fractures. The Harris hip score improved from 49.6 ± 15.5 to 85.2 ± 14.5, and the postoperative Oxford hip score was 19.2 ± 7.6. Multivariable analyses revealed that improvement in Harris hip score increased with cup diameter (beta, 1.28; P = .039).

CONCLUSION

Our data confirmed satisfactory midterm outcomes of uncemented THA using a contemporary DM cup, with no dislocations nor cup revisions due to aseptic loosening.

LEVEL OF EVIDENCE

Level IV, retrospective cohort study.

Dual mobility total hip arthroplasty: should everyone get one?

Hip instability following total hip arthroplasty (THA) remains a major challenge and is one of the main causes of revision surgery.

Dual mobility (DM) implants have been introduced to try to overcome this problem. The DM design consists of a small femoral head captive and mobile within a polyethylene liner.

Numerous studies have shown that DM implants reduce the rate of dislocation compared to fixed-bearing inserts.

Early designs for DM implants had problems with wear and intra-prosthetic dislocations, so their use was restricted to limited indications.

The results of the latest generation of DM prostheses demonstrate that these problems have been overcome. Given the results of these studies presented in this review, surgeons may now consider DM THA for a wider patient selection.

Cite this article: EFORT Open Rev 2019;4:541-547. DOI: 10.1302/2058-5241.4.180045

Use of a Dual mobility cup to prevent hip early arthroplasty dislocation in patients at high falls risk

INTRODUCTION

Hip fracture is a common serious injury that occurs mainly in elderly. Dual-mobility hip arthroplasty or bipolar emiarthroplasty for its treatment remains a controversial decision. Co-morbidities and risk of fall represent additional aspects to be considered. The aim of our study was to determine the rate of mechanical complications for these two types of implants related to fall risk status of patients.

PATIENTS AND METHODS

Our study is a retrospective clinical trial of patients operated with a biarticular hemiarthroplasty or a dual-mobility total hip arthroplasty. Primary outcome was dislocation rate and need for any revision procedure. Patients were treated in a single center from January 2013 to March 2017. In all cases Morse Fall Scale (MSF) was calculated at patient admission to evaluate the risk of postoperative fall. Inclusion criteria to the study were: subcapital or femoral neck fracture of non-pathologic nature, patients with neuromuscular disorders or cognitive dysfunction, age > 75 years with MFS ≥ 45. The patients were reviewed postoperatively at 8 weeks, 6 months, 12 months, and then annually. Patients had clinical (Harris hip score) and radiological assessment.

RESULTS

The mean duration of the follow-up was 283 months. There were five dislocations in Group A (5,6%) and no dislocations in Group B (0%). All dislocations occurred within the first 6 months after surgery. The mean Harris Hip score was 81,7 in Group A patients and 79, 8 in Group B patients.

DISCUSSION

Treatment of hip fractures on non-cooperative patients still represents a dilemma. Falls and runaway motions represent high risk factors of dislocation. Use of dual-mobility cup has been found to be associated with a not statistically proved decrease of dislocation compared to traditional cups.

CONCLUSION

Dual-mobility cups might be considered a valuable option to prevent postoperative dislocation but further study is needed before extending the indications for dual-mobility following a fracture of the femoral neck, to assess the potential cost and complications of a longer procedure. So far, despite a lower dislocation risk, the authors actually cannot recommend widely use of a dual-motility cup instead of emiarthroplasty in high falls risk patients.

Dual-Mobility Constructs in Primary and Revision Total Hip Arthroplasty: A Systematic Review of Comparative Studies

BACKGROUND

Utilization of dual-mobility constructs in total hip arthroplasties (THA) has increased in the recent years. Benefits and risks of these implants in terms of reducing dislocations, long-term survivorship, and associated complications are uncertain when compared to non-dual-mobility articulations.

METHODS

A systematic review of prospective and retrospective studies that compared dual-mobility constructs with controls for primary or revision THAs between 1986 and 2018 was performed. All articles in both English and French were reviewed.

RESULTS

Five studies with primary THAs and 6 with revision THAs were analyzed. For primary THAs, the overall rate of dislocation was 0.9% in the dual-mobility group compared to 6.8% in the control group (P < .001) at a mean follow-up of 7.6 years. The odds ratios for the control group to the dual-mobility group were 4.06 (P < .001) for dislocation, 1.18 (P = .87) for revision, 2.97 (P = .04) for revision due to dislocation, 1.67 (P = .57) for infection, 0.6 (P = .53) for fracture, and 1.21 (P = .81) for aseptic loosening. Similarly, for revision THAs, the overall dislocation rates were 2.2% compared to 7.1% (P < .001) at a mean follow-up of 4.1 years. The odds ratios for the control group to the dual-mobility group were 3.59 (P < .001) for dislocation, 2.46 (P < .001) for re-revision, 4.88 (P = .007) for re-revision due to dislocation, 1.51 (P = .32) for infection, 1.18 (P = .81) for fracture, and 2.71 (P = .003) for aseptic loosening.

CONCLUSION

This systematic review of comparative studies supports the efficacy of dual-mobility constructs to minimize dislocation after both primary and revision THAs in addition to excellent mid-term survivorship compared to control constructs. However, further evidence is needed to evaluate the long-term risks and benefits of dual-mobility constructs in the primary and revision THA setting when compared to contemporary conventional implants.

LEVEL OF EVIDENCE

III, therapeutic.

Cost Analysis of Dual-Mobility Versus Large Femoral Head Constructs in Revision Total Hip Arthroplasty

BACKGROUND

The purpose of this study is to report healthcare payer costs of dual-mobility (DM) and large femoral head (LFH) constructs in revision total hip arthroplasties (THAs).

METHODS

A Markov model was constructed to analyze costs of re-interventions incurred by Medicare and private payers over a 3-year time horizon in patients who underwent unilateral revision THA with DM (n = 126) or LFH (n = 176) implants. Model states and probabilities were derived from prospectively collected registry data. Medicare costs were estimated as the weighted-average national Medicare payment for revision THA. Private payer costs were estimated by using a multiplier of Medicare costs.

RESULTS

Over a 3-year period following revision THA, re-interventions were performed in 11 (9%) DM patients and 34 (19%) LFH patients, costing $263-$1898 in DM THAs and $1285-$3946 in LFH THAs for Medicare. When compared to LFH implants, DM constructs were less costly to Medicare and private payers, resulting in cost differentials of $1536 and $2611, respectively.

CONCLUSIONS

At mid-term follow-up, DM constructs utilized in revision THAs were associated with 11% lower absolute risk of re-intervention and payer savings of $1500-$2500 per case when compared to LFH constructs.

LEVEL OF EVIDENCE

Economic and decision analysis, Level III.

Effect of inclination and anteversion angles on kinematics and contact mechanics of dual mobility hip implants

BACKGROUND

Steep inclination and excessive anteversion angles of acetabular cups could result in adverse edge-loading. This, in turn, increases contact pressure and impingement risk for traditional artificial hip joints. However, the influence of high inclination and anteversion angles on both the kinematics and contact mechanics of dual mobility hip implants has rarely been examined.

METHODS

This study focuses on investigating both the kinematics and contact mechanics of a dual mobility hip implant under different inclination and anteversion angles using a dynamic explicit finite element method developed in a previous study.

FINDINGS

The results showed that an inclination angle of both the back shell and liner ranging from 30° to 70° had little influence on the maximum contact pressure and the accumulated sliding distance of inner and outer surfaces of the liner under normal walking gait. The same results were obtained for an anteversion angle of the liner varying between -20° and +20°. However, when the anteversion angle of the liner was beyond this range, the contact between the femoral neck and the inner rim of the liner occurred. Consequently, this caused a relative rotation at the outer articulation.

INTERPRETATIONS

This suggests that both inclination and modest anteversion angles have little influence on the kinematics and contact mechanics of dual mobility hip implants. However, too excessive anteversion angle could result in a rotation for this kind of hip implant at both articulations.

Mid-Term Outcomes of Dual Mobility Acetabular Cups for Revision Total Hip Arthroplasty

BACKGROUND

This study evaluated (1) survivorship, (2) clinical outcomes, (3) complications, and (4) radiographic outcomes of dual mobility (DM) systems when compared to fixed-bearing prostheses in revision total hip arthroplasty (THA).

METHODS

A cohort of 85 patients who underwent revision THA using DM implants were compared to a prior matching cohort of 170 patients who received fixed-bearing implants. Mean follow-up time was 4 years in the DM cohort and 10 years in the fixed-bearing cohort. Kaplan-Meier analysis was performed to assess survivorships. Clinical outcomes were evaluated using the Harris Hip Score (HHS). Complications and radiographs were evaluated and reported at the final follow-up.

RESULTS

Overall aseptic and all-cause survivorships of the DM cohort were 96.5% and 95.3% compared to 94.7% and 93.5% in fixed-bearing cohort (P = .01 for aseptic and all-cause survivorships). The DM cohort had statistically significant higher survivorship when compared at equivalent follow-up interval in the fixed-bearing cohort. There were 3 aseptic (one due to dislocation) and 1 septic revision in the DM cohort compared to 9 aseptic (6 due to dislocation) and 2 septic revisions in the fixed-bearing cohort. Postoperative HHS scores were 88 and 86 points in the DM and fixed-bearing cohorts. However, the difference in mean improvement in HHS scores from preoperative to postoperative (ΔHHS) was not statistically significant (35 vs 34, P = .533). Except for the aforementioned revisions, there were no progressive radiolucencies or osteolysis on radiographic evaluation in both cohorts.

CONCLUSION

DM articulations demonstrated superior survivorship at equal follow-up intervals when compared to fixed-bearing implants and showed a trend toward lower dislocation rates.

Midterm survival analysis of a cemented dual-mobility cup combined with bone impaction grafting in 102 revision hip arthroplasties

INTRODUCTION

Revision hip arthroplasty is associated with higher dislocation rates than primary hip arthroplasty. A dual-mobility cup (DMC) can reduce this risk. Another problem is destruction of the acetabulum, induced by aseptic loosening of the prosthesis. Bone impaction grafting (BIG) can be used to reconstruct these defects, but is usually performed with cemented all polyethylene cups. The purpose of this study is to evaluate midterm cup survival and dislocation rate for the combination of BIG and DMC.

METHODS

Between 2007 and 2013, 96 patients received 102 DMCs combined with BIG of the acetabulum during revision surgery. These data were first compared with a control group, consisting of 59 cases from the same hospital receiving a cemented all polyethylene cup combined with BIG. In addition, the control group was expanded with 41 cases operated on in 2007 in 'an orthopaedic centre of excellence', resulting in a 'combined control group' of 100 patients. Log-rank tests and chi-square tests were used to compare survival and dislocation rates, respectively.

RESULTS

Cumulative survival of the DMC was 95.8% (range 3 months-7 years). This was comparable to the survival in the control groups (96.5% and 94.7%). The dislocation rate of 2.9% (3/102) in the dual-mobility group was lower (p = 0.02) compared to the dislocation rate of 11.8% (7/59) in the control group, but not (p = 0.12) compared to 8% in the combined control group (8/100).

CONCLUSIONS

This study shows that combining a DMC with BIG does not compromise outcome in terms of midterm survival of the cup.

Dual-Mobility vs Fixed-Bearing Total Hip Arthroplasty in Patients Under 55 Years of Age: A Single-Institution, Matched-Cohort Analysis

BACKGROUND

Prosthetic dislocation of total hip arthroplasty (THA) is a common cause for revision surgery. Dual-mobility (DM) bearings were introduced to mitigate complications; however, their performance in younger patients is unknown. This study compared results of patients <55 years of age with DM vs fixed-bearing (FB) primary THA.

METHODS

Our total joint registry was used to evaluate primary THA patients <55 years of age, and then, an age-matched comparative analysis was performed for 136 THAs using third-generation highly cross-linked polyethylene DM bearings and 136 THAs using FB from the same manufacturer with mean follow-up of 3.2 and 3.4 years, respectively. Mean age at surgery was 48.4 and 48.5 years, respectively. There was no difference in gender distribution. Incidence of complications (eg, dislocation) was evaluated and compared statistically. Patient-reported outcomes using the Modified Harris Hip Score were available. Normally distributed continuous data were compared using the Student t test, and discrete data were compared using the Fisher exact test (P < .05).

RESULTS

There were no dislocations or intraprosthetic dissociations (0%) in the DM group and 7 (5.1%) dislocations in the FB group (P = .01) at the mean follow-up of 3 years postoperatively. Two of the 7 unstable patients in the FB cohort were revised for recurrent instability (1.5%). There was no difference in postoperative Modified Harris Hip Score between the DM (87.2 ± 16.6) and the control cohorts (87.9 ± 13.7; P = .78).

CONCLUSION

DM bearings in patients <55 years of age show excellent results for prosthetic stability when compared with patients who undergo FB.

The influence of spine-hip relations on total hip replacement: A systematic review

Sagittal pelvic kinematics along with spino-pelvic angular parameters have recently been studied by numerous investigators for their effect on total hip replacement (THR) clinical outcomes, but many issue of spine-hip relations (SHR) are currently unexplored. Therefore, our review aims at clarifying the following questions: is there any evidence of a relationship between articular impingement/dislocation risk in primary THR and (1) certain sagittal pelvic kinematics patterns, (2) pelvic incidence, and (3) types of SHRs? A systematic review of the existing literature utilising PubMed and Google search engines was performed in January 2017. Only clinical or computational studies published in peer-reviewed journals over the last five years in either English or French were reviewed. We identified 769 reports, of which 12 met our eligibility criteria. A review of literature shows that sagittal pelvic kinematics, but not the pelvic incidence, influences the risk of prosthetic impingement/dislocation. We found no study having assessed the relationship between this risk and the types of SHRs. Sagittal pelvic kinematics is highly variable among individuals and certain kinematic patterns substantially influences the risk of prosthetic impingement/dislocation. Recommendations for cup positioning are therefore switching from a systematic to a patient-specific approach, with the standing cup orientation Lewinneck safe zone progressively giving way to a new parameter of interest: the functional orientation of the cup. Based on a recently published classification for SHRs, We propose a new concept of "kinematically aligned THR" for the purposes of THR planning. Further studies are needed to investigate the relevance of such a classification towards the assumptions and hypothesis we have made. Level of evidence,- Level IV, systematic review of level III and IV studies.

The Cost-Effectiveness of Dual Mobility Implants for Primary Total Hip Arthroplasty: A Computer-Based Cost-Utility Model

BACKGROUND

Dislocation remains a clinically important problem following primary total hip arthroplasty, and it is a common reason for revision total hip arthroplasty. Dual mobility (DM) implants decrease the risk of dislocation but can be more expensive than conventional implants and have idiosyncratic failure mechanisms. The purpose of this study was to investigate the cost-effectiveness of DM implants compared with conventional bearings for primary total hip arthroplasty.

METHODS

Markov model analysis was conducted from the societal perspective with use of direct and indirect costs. Costs, expressed in 2013 U.S. dollars, were derived from the literature, the National Inpatient Sample, and the Centers for Medicare & Medicaid Services. Effectiveness was expressed in quality-adjusted life years (QALYs). The model was populated with health state utilities and state transition probabilities derived from previously published literature. The analysis was performed for a patient's lifetime, and costs and effectiveness were discounted at 3% annually. The principal outcome was the incremental cost-effectiveness ratio (ICER), with a willingness-to-pay threshold of $100,000/QALY. Sensitivity analyses were performed to explore relevant uncertainty.

RESULTS

In the base case, DM total hip arthroplasty showed absolute dominance over conventional total hip arthroplasty, with lower accrued costs ($39,008 versus $40,031 U.S. dollars) and higher accrued utility (13.18 versus 13.13 QALYs) indicating cost-savings. DM total hip arthroplasty ceased being cost-saving when its implant costs exceeded those of conventional total hip arthroplasty by $1,023, and the cost-effectiveness threshold for DM implants was $5,287 greater than that for conventional implants. DM was not cost-effective when the annualized incremental probability of revision from any unforeseen failure mechanism or mechanisms exceeded 0.29%. The probability of intraprosthetic dislocation exerted the most influence on model results.

CONCLUSIONS

This model determined that, compared with conventional bearings, DM implants can be cost-saving for routine primary total hip arthroplasty, from the societal perspective, if newer-generation DM implants meet specific economic and clinical benchmarks. The differences between these thresholds and the performance of other contemporary bearings were frequently quite narrow. The results have potential application to the postmarket surveillance of newer-generation DM components.

LEVEL OF EVIDENCE

Economic and decision analysis Level III. See Instructions for Authors for a complete description of levels of evidence.

The unstable total hip arthroplasty

One of the most common causes for revision surgery following total hip arthroplasty (THA) is dislocation.

Dislocation is associated with a considerable amount of suffering and risks for the patient, and extra costs for the health care system.

Compared with degenerative arthritis, the dislocation rate is doubled for avascular necrosis and multiplied by three times for congenital dislocation, four for fracture, five for nonunion, malunion or a failed hip arthroplasty, and eleven times after surgery for prosthetic instability.

In analysing instability the cause may be assessed as 1) locally caused within the hip with explanatory radiographic findings, 2) locally caused without explanatory radiographic findings or 3) non-locally caused, i.e. non-compliant patient, neuromuscular or cognitive disorders.

Revision strategies for instability are typically directed to correct the underlying aetiology, but also to strive for an upsizing of the head and liner.

Cite this article: Ullmark G. The unstable total hip arthroplasty. EFORT Open Rev 2016;1:83-88. DOI: 10.1302/2058-5241.1.000022.

No dislocations after primary hip arthroplasty with the dual mobility cup in displaced femoral neck fracture in patients with dementia. A one-year follow-up in 20 patients

Purpose: The aim of this study was to describe the dislocation rates, reoperation rates and mortality 30 day and one year following THA with AVANTAGE^® dual mobility cup among dementia patients with an acute displaced intracapsular femoral neck fracture.

Patients and methods: From 2010 to 2014 we identified 20 hip fracture patients with dementia, who have had total hip arthroplasty with the AVANTAGE^® dual mobility cup. The primary outcome was dislocation. Secondary outcomes were revision surgery, 30 days and one year mortality, time to surgery and length of hospital stay.

Results: Follow-up time was one year. None of the patients experienced dislocation or received revision surgery in the follow-up period. The 30-days mortality rate was 25% (confidence interval (CI) 95%; 4–46%) and the one year mortality was 45% (CI 95%; 21–69). Mean time to surgery was 27 h (CI 95%; 20–37 h) and mean length of hospital stay was 5.5 days (CI 95%; 4, 0–7, 6 days).

Conclusion: THA with the dual-mobility cup seems favourable in the treatment of patients with a displaced femoral neck fracture and patients with dementia. Correct placement of the cup is pivotal and technically demanding. Not all orthopedic surgeons perform total hip arthroplasty while challenges regarding the logistics can be encountered since time to surgery is known to affect the mortality negatively.

Comparison of dual-mobility cup and unipolar cup for prevention of dislocation after revision total hip arthroplasty

Background and purpose - Revision total hip arthroplasty (THA) is associated with higher dislocation rates than primary THA. We compared the risk of dislocation within 6 months and all-cause re-revision during the whole study period using either the dual-mobility cup or the unipolar cup. Methods - We used a prospective hospital registry-based cohort including all total and cup-only revision THAs performed between 2003 and 2013. The cups used were either dual-mobility or unipolar; the choice was made according to the preference of the surgeon. 316 revision THAs were included. The mean age of the cohort was 69 (25-98) years and 160 THAs (51%) were performed in women. The dual-mobility group (group 1) included 150 THAs (48%) and the mean length of follow-up was 31 (0-128) months. The unipolar group (group 2) included 166 THAs (53%) and the mean length of follow-up was 52 (0-136) months. Results - The incidence of dislocation within 6 months was significantly lower with the dual-mobility cup than with the unipolar cup (2.7% vs. 7.8%). The unadjusted risk ratio (RR) was 0.34 (95% CI: 0.11-1.02) and the adjusted RR was 0.28 (95% CI: 0.09-0.87). The number of patients needed to treat with a dual-mobility cup in order to prevent 1 case of dislocation was 19. The unadjusted incidence rate ratio for all-cause re-revision in the dual-mobility group compared to the unipolar group was 0.6 (95% CI: 0.3-1.4). Interpretation - Use of a dual-mobility rather than a unipolar cup in revision THA reduced the risk of dislocation within 6 months.

Early experience with dual mobility acetabular systems featuring highly cross-linked polyethylene liners for primary hip arthroplasty in patients under fifty five years of age: an international multi-centre preliminary study

PURPOSE

To evaluate early performance of contemporary dual mobility acetabular systems with second generation annealed highly cross-linked polyethylene for primary hip arthroplasty of patients under 55 years of age.

METHODS

A prospective observational five years study across five centers in Europe and the USA of 321 patients with a mean age of 48.1 years was performed. Patients were assessed for causes of revision, hip instability, intra-prosthetic dissociation, Harris hip score and radiological signs of osteolysis.

RESULTS

There were no dislocations and no intra-prosthetic dissociations. Kaplan Meier analysis demonstrated 97.51% survivorship for all cause revision and 99.68% survivorship for acetabular component revision at five years. Mean Harris hip score was 93.6. Two acetabular shells were revised for neck-rim implant impingement without dislocation and ten femoral stems were revised for causes unrelated to dual mobility implants.

CONCLUSION

Contemporary highly cross-linked polyethylene dual mobility systems demonstrate excellent early clinical, radiological, and survivorship results in a cohort of patients that demand high performance from their implants. It is envisaged that DM and second generation annealed HXLPE may reduce THA instability and wear, the two most common causes of THA revision in hip arthroplasty.

Benefit and risk in short term after total hip arthroplasty by direct anterior approach combined with dual mobility cup

PURPOSE

No previous reports have described the benefits and risks associated with the dual mobility cup (DMC) in primary THA via direct anterior approach (DAA). The aim of this study was to compare the safety and rate of early postoperative complication of the DAA with the DMC for THA with those of the DAA with a single standard cup, and to investigate the influence of the learning curve of the use of DMC on intra- and perioperative outcomes.

METHODS

We retrospectively investigated 60 hips treated in the single-DAA group and 60 hips treated in the dual-DAA group. A primary/secondary outcome variable was the presence of any intra- or perioperative complication within the first 6 months/the operative time and hip function at 6 months postoperatively. We also analyzed influence of the learning curve of the use of DMC on intra- and perioperative outcomes.

RESULTS

No intraoperative complications were observed in either group. One anterior dislocation and one periprosthetic hip fracture were occurred in the single-DAA group. The surgical times in the single-DAA and dual-DAA groups were 112.0 ± 20.9 and 121.0 ± 26.9 min (p < 0.001). There was no significant difference in the 6-month postoperative hip function scores between the two groups. There was no influence of the learning curve of the use of DMC on intra- and perioperative outcomes.

CONCLUSION

We have demonstrated the short-term safety and lack of inferiority of using the DMC in the DAA compared with the standard single mobility cup.

Cost-effectiveness model comparing dual-mobility to fixed-bearing designs for total hip replacement in France

BACKGROUND

Instability is among the main causes of total hip arthroplasty (THA) failure. In clinical studies, THA with a dual-mobility cup (THA-DM) decreased the risk of instability after primary THA compared to THA with a fixed-bearing design (THA-FB). However, whether THA-DM is more cost-effective than THA-FB has not been established using Markov modelling with determination of the incremental cost-effectiveness ratio (ICER). The objectives of this work were to: (1) measure the efficiency of these two options, (2) use the nationwide hospital electronic database (PMSI) to estimate direct costs of dislocations and revisions for instability, and (3) conduct deterministic and probabilistic sensitivity analyses to estimate potential mean annual cost-savings in France.

HYPOTHESIS

We hypothesised that primary THA-DM was cost-saving compared to primary THA-FB.

MATERIAL AND METHODS

In the database, we identified 80,405 patients who had THA in 2009 and we collected their outcomes over 4 years (2009-2012). Cost-effectiveness was assessed based on the costs of resources used for all consequences of prosthetic dislocation and paid for by the statutory health insurance system or other sources.

RESULTS

THA-DM was associated with a relative risk of dislocation of 0.4 versus THA-FB. This risk difference translated into 3283 fewer dislocations per 100,000 patients with THA-DM. The corresponding cost-savings for the 140,000 primary THA procedures done in France annually was 39.62 million Euros. A relative risk of 0.2 would yield annual cost-savings of 56.28 million Euros. In the probabilistic sensitivity analysis, THA-DM was the less costly option under all hypotheses, with potential maximum cost-savings of more than 100 million Euros per year in France.

DISCUSSION

This comparative cost-effectiveness analysis suggests that THA-DM may induce substantial cost-savings compared to THA-FB. This possibility should be assessed by long-term clinical studies of new-generation DM prostheses.

Effect of friction and clearance on kinematics and contact mechanics of dual mobility hip implant

The dual mobility hip implant has been introduced recently and increasingly used in total hip replacement to maintain the stability and reduce the risk of post-surgery dislocation. However, the kinematics and contact mechanisms of dual mobility hip implants have not been investigated in detail in the literature. Therefore, finite element method was adopted in this study to investigate dynamics and contact mechanics of a typical metal-on-polymer dual mobility hip implant under different friction coefficient ratios between the inner and the outer articulations and clearances/interferences between the ultra-high-molecular-weight polyethylene liner and the metal back shell. A critical ratio of friction coefficients between the two pairs of contact interfaces was found to mainly determine the rotating surfaces. Furthermore, an initial clearance between the liner and the back shell facilitated the rotation of the liner while an initial interference prevented such a motion at the outer articulating interface. In addition, the contact area and the sliding distance at the outer articulating surface were markedly greater than those at the inner cup-head interface, potentially leading to extensive wear at the outer surface of the liner.

Finite element analysis of sliding distance and contact mechanics of hip implant under dynamic walking conditions

An explicit finite element method was developed to predict the dynamic behavior of the contact mechanics for a hip implant under normal walking conditions. Two key parameters of mesh sensitivity and time steps were examined to balance the accuracy and computational cost. Both the maximum contact pressure and accumulated sliding distance showed good agreement with those in the previous studies using the implicit finite element analysis and analytical methods. Therefore, the explicit finite element method could be used to predict the contact pressure and accumulated sliding distance for an artificial hip joint simultaneously in dynamic manner.

Intraprosthetic Dislocation of Dual-Mobility Bearings Associated with Closed Reduction

CASE

We present two patients with dual-mobility total hip arthroplasty components who underwent closed reduction of posterior dislocations with conscious sedation in the emergency room. Following closed reduction, both patients had immediate pain, clicking, and grinding of the hip. Radiographs identified intraprosthetic dislocation of the dual-mobility components, and revision surgery was required.

CONCLUSION

When dislocation of a dual-mobility bearing occurs, the surgeon should consider performing a careful closed reduction with muscle paralysis and use of fluoroscopic guidance in the operating room to avoid intraprosthetic dislocation.

Dual mobility bearings withstand loading from steeper cup-inclinations without substantial wear

Steep cup abduction angles with adverse joint loading may increase traditional polyethylene bearing wear in total hip arthroplasties. However, there have been few reports evaluating the effect of cup inclination on the wear of dual-mobility devices. In a hip joint simulation, we compared the short-term wear of two-sizes of modular highly cross-linked dual-mobility bearings (28 mm femoral head diameter/42 mm polyethylene insert outer diameter/54 mm acetabular shell diameter; 22.2 mm femoral head diameter/36 mm polyethylene insert outer diameter/48 mm acetabular shell diameter) at 50 and 65° of cup inclination with modular 28 mm femoral head on 54 mm cup diameter metal-on-highly cross-linked polyethylene bearings. Increasing inclination from 50-65° had no changes in volumetric wear of 28/42/54 mm (mean, 1.7 vs. 1.2 mm3 /million cycles, respectively; p = 0.50) and 22.2/36/48 mm (mean, 1.7 vs. 1.2 mm3/million cycles, respectively; p = 0.48) dual mobility bearings. At 65°, 22.2/36/48 mm dual-mobility bearings had lower volumetric loss (mean, 2.2 vs. 6.3 mm(3) ; p = 0.03) and wear rates (mean, 1.2 vs. 2.7 mm3/million cycles; p = 0.02) compared to metal-on-highly cross-linked polyethylene bearings. Modern-generation dual-mobility designs with highly cross-linked polyethylenes may potentially withstand edge-loading from steeper cup-inclinations without substantial decreases in wear.

Dual mobility cup reduces dislocation and re-operation when used to treat displaced femoral neck fractures

PURPOSE

Total hip arthroplasty (THA) as primary treatment for displaced femoral neck fractures is controversial as THA is associated with higher rates of dislocation but lower rates of re-operation compared to hemiarthroplasty (HA). A dual mobility cup (DMC) design is associated with lower dislocation and re-operation rates in elective surgery. Is this also the case when used to treat displaced femoral neck fractures? The aim of this study is to compare rates of dislocation and re-operation of any kind following treatment for displaced femoral neck fractures with either bipolar HA or THA with DMC.

METHODS

Two consecutive groups of patients treated for displaced femoral neck fractures at the Regional Hospital in Viborg in Denmark were included. In 2007-2008 171 patients (mean age 84.1 years) were treated with bipolar HA. In 2009-2010 175 patients (mean age 75.2 years) were treated with THA with DMC. Data regarding rates of dislocation and re-operation were obtained by retrospective review of medical records.

RESULTS

We found a statistically significant difference regarding rates of dislocation and re-operation of any kind in favour of THA with DMC. Dislocation occurred in 25/171 patients [95 % confidence interval (CI) 9.3-19.9 %] treated with bipolar HA and 8/175 patients (95 % CI 1.5-7.7 %) treated with THA with DMC (p = 0.002). Re-operations were required in 32/171 patients (95 % CI 12.9-24.6 %) treated with bipolar HA and 16/175 patients (95 % CI 4.8-13.4 %) treated with THA with DMC (p = 0.01).

CONCLUSIONS

Our findings indicate that THA with DMC is superior to bipolar HA following treatment for displaced femoral neck fractures in regard to rates of dislocation and re-operation.

Computerized range of motion analysis following dual mobility total hip arthroplasty, traditional total hip arthroplasty, and hip resurfacing

Newer arthroplasty designs claim to provide superior range of motion (ROM) and greater stability than their predecessors. However, there is no way to compare ROM of implant systems in an equivalent anatomical environment in a clinical setting. This study used computer-aided design to compare ROM after hip resurfacing, 28 mm THA, 36 mm THA, and anatomic dual mobility (ADM) THA in 3D models of 5 cadaver pelvises. ROM to impingement was then tested in 10 different motions and a one-way ANOVA was used to compare results. The hip resurfacing resulted in restricted ROM compared to the other 3 models in all motions except adduction. The ADM, 36 mm, and 28 mm THA resulted in similar ROM. Dual mobility constructs provide comparable ROM in patients where large head THA is not appropriate.

Dual mobility cups for preventing early hip arthroplasty dislocation in patients at risk: experience in a county hospital

Dislocation remains a major concern after hip arthroplasty. We asked whether dual mobility cups (DMC) would improve early hip stability in patients with high risk of dislocation. We followed 34 patients (21 females, 13 males) treated between 2009 and 2012 with cemented DMC for hip revisions caused recurrent hip prosthetic dislocation or as a primary procedure in patients with high risk of instability. Functional outcome and quality of life were evaluated using Harris Hip Score and EQ-5D respectively. We found that the cemented DMC gave stability in 94%. Seven patients (20%) were re-operated due to infection. One patient sustained a periprosthetic fracture. At follow-up (6 to 36 months, mean 18), the mean Harris hip score was 67 (standard deviation: 14) and mean EQ-5D was 0.76 (standard deviation: 0.12). We concluded that treating patients with high risk of dislocation with DMC can give good stability. However, complications such as postoperative infection can be frequent and should be managed carefully.