Wear performance evaluation of a contemporary dual mobility hip bearing using multiple hip simulator testing conditions

Polyethylene Dual Mobility Liners Show Minimal Polyethylene Changes in Early Retrievals

BACKGROUND

Dual mobility (DM) liners were introduced to reduce instability in total hip arthroplasty. They were found to allow for motion predominantly at the femoral head and the inner bearing of the acetabular liner; however, little is known if this motion is sufficient to alter polyethylene material characteristics. We assessed cross-link (XL) density and oxidation index (OI) measurements of the inner and outer bearing articulations.

METHODS

Thirty-seven DM liners were collected with a duration of implantation greater than 2 years. Clinical and demographic data were collected from a chart review. A cylinder was cored from the apex of each liner and cut into 4.5 mm long inner and outer diameter segments for XL density swell ratio testing. The OI was measured from sagittal 100 μm microtome slices using Fourier transform infrared spectroscopy. Student's t-tests were used to determine differences in OI and XL density between the bearings. Spearman's correlation assessed relationships between patient demographics, OI, and XL density. Duration of implantation for the cohort was a mean of 35 (range, 24-96) months.

RESULTS

The inner and outer bearing had similar median XL densities (0.17 mol/dm3 versus 0.17 mol/dm3, P = .6). The inner bearing had an increased OI when compared to the outer bearing (0.16 versus 0.13, P = .008). The OI was inversely correlated with XL density (r = -0.50, P = .002).

CONCLUSION

Small differences were found in oxidation between the inner and outer bearing of the DM construct. Failures at an average of 3 years indicate low levels of oxidation, unlikely to impact the mechanical properties of the material.

Do articular surfaces of dual mobility hips have more wear and friction? An in vitro investigation

INTRODUCTION

Larger head-to-neck ratio of dual mobility (DM) hip arthroplasties provide greater range of motion/less risk of dislocation, but raise concerns for high wear and friction. We measured in vitro, the wear rates of contemporary DM hips with highly-crosslinked Ultra High Molecular Weight Polyethylene (UHWMPE), where it came from, and their frictional torques.

METHODS

Hip simulators were used to compare the wear of DM to fixed-bearing (FB) designs of two different implants. Each of eight different configurations underwent millions of simulated walking cycle tests, some as full DM, some as FB controls, some DM with the outer-articulation deliberately immobilized, and some the inner. Wear and three-dimensional-frictional torques were measured and friction independent of size was deduced.

RESULTS

The DM hips produced lower wear and friction-torque than the FB hips. The DM Wear during walking gait comes mostly from the smaller inner articular surface. If the outer surface was immobilized, the wear and torque of the inner alone would be small, but the full DM (inner and outer free-to-move) wear and torque were smallest of all. Friction measurements expectedly showed larger hips having higher frictional torques, but the DM showed the lowest, again because its motion was mostly the smaller inner articulation; smaller than even a modern fixed-bearing hip.

CONCLUSION

The DM hips appear to combine the benefits of greater range of motion and less impingement of larger hips, with the lower wear and friction of smaller FB hips, with some benefits compromised if the outer or inner articulations are immobilized.

The Role of Dual-Mobility Components in Total Hip Arthroplasty

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Dual mobility (DM) refers to a now widely available option for total hip articulation. DM implants feature a small inner head, a hard bearing, that connects via a taper fit onto the femoral trunnion. This head freely rotates but is encased inside a larger, outer polyethylene head that articulates with a smooth acetabular component.

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DM acetabular components are available in the form of a monoblock shell or as a liner that is impacted into a modular shell, providing a metal articulation for the polyethylene outer head.

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DM is designed to increase hip stability by providing the arthroplasty construct with a higher jump distance, head-to-neck ratio, and range of motion prior to impingement.

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The use of DM in total hip arthroplasty continues to increase in the United States for both primary and revision arthroplasty. Surgeons should be aware of the potential benefits and pitfalls.

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Long-term data are lacking, especially for modular DM implants. Points of concern include a potential for accelerated polyethylene wear, intraprosthetic dislocation, and modular backside fretting corrosion.

Dual-Mobility Cups in Primary Total Hip Arthroplasty

Dual-mobility cups (DMCs) were introduced in France more than 40 years ago and are increasingly used not only in hip revision but also primary hip arthroplasty. Due to a simulated large-head articulation and increased jumping distance, DMCs can contribute to a high range of motion in the hip joint and reduce the risk of instability. Numerous studies have reported low dislocation rates and high survival rates in the mid-term follow-up. Nevertheless, long-term data, especially on primary hip replacement, remain limited, and the effect of recent designs and material innovations is still unclear. Therefore, primary DMCs are mainly proposed in patients at high risk for dislocation (i.e. pelvitrochanteric insufficiency, compromised spinopelvic mobility, neuromuscular disorders, obesity and femoral neck fractures). Based on a review of recently published studies referring to these indications, the current study discusses the advantages and disadvantages of DMCs.

Direct Cementation of Dual Mobility Cups Into the Bony Acetabulum in Primary Total Hip Arthroplasty: Clinical and Radiographic Outcomes at a Minimum 5-Year Follow-Up

BACKGROUND

Cemented dual mobility cups (DMCs) are commonly used in combination with acetabular reinforcement devices. Indeed, according to literature, direct cementation of metal-backed acetabular components into the bony acetabulum remains controversial as this technique is potentially associated with increased rates of aseptic loosening. Therefore, this study aimed to evaluate the clinical and radiographic outcomes of DMC cemented into the bony acetabulum in primary total hip arthroplasty (THA).

METHODS

A total of 49 THA (48 patients, mean age 78 years [range, 51 to 91]) performed with direct cementation of a DMC into the bony acetabulum were prospectively included in our total joint registry and retrospectively reviewed. The clinical outcome was assessed using the Harris hip score (HHS). The radiographic outcome included measurement of component positioning and occurrence and progression of demarcation around the cemented DMC. Complications were reported with a particular attention to cemented fixation failure and aseptic loosening.

RESULTS

At a 7-year mean follow-up (range, 5 to 8), the pre-to postoperative HHS improved from 47 (range, 30 to 58) to 92 points (range, 80 to 98) (P < .01). Nonprogressive and focalized demarcations were observed in 7 THA (14%). Importantly, no progressive demarcation or DMC aseptic loosening was observed.

CONCLUSION

Direct cementation of DMC into the bony acetabulum ensured a stable fixation with no progressive demarcation or aseptic loosening at midterm follow-up. Therefore, this technique can be selectively considered in primary THA, especially in elderly or frail patients to avoid potential mechanical failure of press-fit fixation due to altered bone quality or additional morbidity related to the use of acetabular reinforcement devices.

Which femoral neck for a dual mobility cup? A biomechanical evaluation

Purpose

This study aimed to evaluate polyethylene (PE) damage and wear lesions to the chamfer of mobile components under mobile and fixed femoral neck impingement at the third articulation, and to determine which femoral neck characteristics should be considered with a dual mobility cup to limit those lesions.

Methods

Two femoral neck geometries (cylindrical and quadrangular) with two surface finishing roughness (rough and polished), and two head-to-neck ratios (28- and 22.2-mm diameter femoral heads) were evaluated in a hip simulator testing. For each characteristic, six femoral necks were tested with six dual mobility cups under fixed and mobile femoral neck impingement conditions. Chamfer PE damage and volumetric wear were evaluated and compared for each femoral neck characteristic and impingement condition.

Results

Under mobile impingement condition, femoral neck characteristics did not significantly affect PE damage and wear lesions to the chamfer (p = 0.283 to 0.810). However, under fixed impingement condition, significantly higher PE damage and wear lesions to the chamfer were produced by the quadrangular geometry compared to the cylindrical geometry (p = 0.004 to 0.025). In addition, with the quadrangular geometry, rough surface finishing was demonstrated to increase volumetric wear of the chamfer (p = 0.009). No significant influence of head-to-neck ratio was observed on PE damage and wear lesions to the chamfer (p = 0.244 to 0.714).

Discussion

This biomechanical study emphasized that femoral neck characteristics are critical with dual mobility cup and tend to favor a cylindrical geometry particularly whether fixed impingement at the third articulation occurs.

Personalized Hip Joint Replacement with Large Diameter Head: Current Concepts

Hip arthroplasty is a common procedure in elective orthopaedic surgery that has excellent outcomes. Hip replacement surgery aims to create a “forgotten” joint, i.e., a pain-free joint akin to a native articulation. To achieve such goals, hip arthroplasty must be personalised. This is achieved by restoring: the centre of rotation of the native hip; leg length equality; femoral offset; femoral orientation; soft tissue tension; joint stability with an unrestricted hip range of motion; and having appropriate stress transfer to the bone. In addition, the whole pathway should provide an uneventful and swift postoperative recovery and lifetime implant survivorship with unrestricted activities. At our institution, the preferred option is a personalized total hip arthroplasty (THA) with a large diameter head (LDH) using either monobloc or dual-mobility configuration for the acetabular component. LDH THA offers an impingement-free range of motion and a reduced risk of dislocation. The larger head-neck offset allows for a supraphysiologic range of motion (ROM). This can compensate for a patient’s abnormal spinopelvic mobility and surgical imprecision. Additionally, LDH bearing with a small clearance exerts a high suction force, which provides greater hip micro-stability. With appropriate biomechanical reconstruction, LDH THA can restore normal gait parameters. This results in unrestricted activities and higher patient satisfaction scores. We use LDH ceramic on ceramic for our patients with a life expectancy of more than 20 years and use LDH dual mobility bearings for all others.

The usefulness of dual mobility cups in primary total hip arthroplasty patients at a risk of dislocation

This study aimed to evaluate the early results of primary total hip arthroplasty (THA) using dual mobility (DM) cups in patients at a risk of dislocation and compare them with that of fixed bearing (FB) THA. This retrospective study included patients who had undergone primary THA between January 2016 and December 2018 and were at a risk of dislocation. A propensity score-matched analysis was conducted for 63 THA procedures with vitamin-E infused highly cross-linked polyethylene (VEPE) DM bearing and 63 THA procedures performed with FB from the same manufacturer for a mean follow-up period of 3.1 and 3.5 years, respectively. The radiologic outcomes at the last follow-up and incidence of postoperative complications were evaluated and compared statistically between the two groups. The modified Harris hip score (mHHS) was used to assess patient-reported outcomes. Postoperative dislocation occurred in 4 cases (6.3%) in the FB group, but did not occur in the DM group (p = 0.042). There was no difference in the radiologic outcomes and postoperative complications between the two groups. The mHHS at the last follow-up showed satisfactory outcomes in both the groups (DM group, 90.5; FB group, 88.1), without a statistical difference between the groups. The early results of THA using VEPE DM bearing showed better outcomes than that of THA with FB for patients at a risk of dislocation. A longer follow-up period is recommended to assess the stability and overall outcomes.

Polyethylene wear of dual mobility cups: a comparative analysis based on patient-specific finite element modeling

Purpose

Concerns remain about potential increased wear with dual mobility cups related to the multiple articulations involved in this specific design of implant. This finite element analysis study aimed to compare polyethylene (PE) wear between dual mobility cup and conventional acetabular component, and between the use of conventional ultra-high molecular weight PE (UHMWPE) and highly cross-linked PE (XPLE).

Methods

Patient-specific finite element modeling was developed for 15 patients undergoing primary total hip arthroplasty (THA). Five acetabular components were 3D modeled and compared in THA constructs replicating existing implants: a dual mobility cup with a 22.2-mm-diameter femoral head against UHMWPE or XLPE (DM22PE or DM22XL), a conventional cup with a 22.2-mm-diameter femoral head against UHMWPE (SD22PE) and a conventional cup with a 32-mm-diameter femoral head against UHMWPE or XLPE (SD32PE or SD32XL).

Results

DM22PE produced 4.6 times and 5.1 times more volumetric wear than SD32XL and DM22XL (p < 0.0001, Cohen’s d = 6.97 and 7.11; respectively). However, even if significant, the differences in volumetric wear between DM22XL and SD32XL as well as between DM22PE and SD22PE or SD32PE were small according to their effect size (p < 0.0001, Cohen’s |d|= 0.48 to 0.65) and could be therefore considered as clinically negligible.

Conclusion

When using XLPE instead of UHMWPE, dual mobility cup with a 22.2-mm-diameter femoral head produced a similar amount of volumetric wear than conventional acetabular component with a 32-mm-diameter femoral head against XLPE. Therefore, XLPE is advocated in dual mobility cup to improve its wear performance.

Acetabular Component and Liner Selection for the Prevention of Dislocation After Primary Total Hip Arthroplasty

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Primary total hip arthroplasty (THA) is a reproducible and efficacious procedure for patients with end-stage osteoarthritis; however, dislocation remains the most common cause of revision arthroplasty.

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Technological advancements in acetabular component design and liner options, in conjunction with a more comprehensive understanding of the spinopelvic factors that influence dislocation, will likely reduce the risk of dislocation and revision over time.

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The contemporary liner and shell options for primary THA, in order of increasing constraint and stability, include (1) neutral, (2) lateralized, (3) face-changing (oblique), (4) lipped (high-wall) with or without lateralization, (5) modular and anatomic dual-mobility, and (6) constrained options.

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Different liner designs can alter functional anteversion, inclination, and jump distance, and can be used to minimize a single predictable dislocation vector (lipped [high-wall] liners) or multiple vectors of instability risk when the dislocation direction is unpredictable (dual-mobility liners).

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Liner selection should be based on the patient-specific risk of dislocation, including static anatomic (e.g., large anterior inferior iliac spine or greater trochanter morphology), dynamic anatomic (e.g., limited sitting-standing change in the sacral slope), and demographic or medical (e.g., neurocognitive disorders and obesity) risk factors.

Dual Mobility in Total Hip Arthroplasty: Biomechanics, Indications and Complications-Current Concepts

Dual-mobility (DM) articulations are increasingly utilized to prevent or manage hip instability after total hip arthroplasty (THA). DM cups offer enhanced stability due to the dual articulation resulting in larger jump distance and greater range of motion before impingement. Improvement in design features and biomaterials has contributed to increased interest in dual-mobility articulations due to lower risk of complications compared to their historic rates. The incidence of implant-specific complications like intra-prosthetic dislocation (IPD) and wear has reduced with newer-generation implants. DM THAs are used in primary THA in patients with high risk for dislocation, e.g. neuromuscular disorder, femoral neck fracture, spinopelvic deformity, etc. They offer an attractive alternative option to constrained liner for treatment of hip instability in revision THA. The medium- to short-term results with DM THA have been encouraging in primary and revision THA. However, there are concerns of fretting, corrosion and long-term survivorship with DM THA. Hence, longer-term studies and surveillance are required for the safe use of DM THA in clinical practice.

Superior functional outcome with dual mobility THR as compared to conventional THR in fracture neck femur: a prospective cohort study

Introduction: Total Hip Replacement (THR) in displaced Fracture Neck of Femur (FNOF) is associated with higher dislocation rates. Conventional THR with a large femoral head and anterior approach has reduced the instability, but it remains higher than THR done for other aetiology. Recent studies have shown reduced dislocation rates with dual mobility THR (DMTHR) for FNOF; however, there is a lack of comparative research to show its superiority over conventional THR. Further, its role in the Asian subcontinent, where the patient requires sitting cross-legged or squatting, has not been studied. Methods: A prospective cohort study of 103 elderly patients with displaced FNOF with a minimum follow-up of 1-year. Fifty-two patients were operated on with DMTHR and fifty-one patients with conventional THR. Both the groups were matched in terms of demographic data, surgical approach, and postoperative protocol. Radiological and functional outcomes in terms of Harris Hip Score (HHS), Range of motion, Patient Reported Outcome Measures (PROM), and Dislocation rate were compared between the two groups. Results: Mean HHS of the DMTHR group was 76.37 at three months and 87.02 at the end of the 1-year postoperatively, which was significantly better than the conventional THR group 65.65 at three months and 72.96 at 1-year. The range of motion was significantly better in the DMTHR group than the conventional THR group. There was no significant difference in radiological outcomes and postoperative dislocation rate between the two groups. Conclusion: Dual mobility implants give better results than conventional implants for primary THA in elderly patients of displaced FNOF regarding better function and greater range of motion.

Dual Mobility Reduces Dislocations-Why I Use It in All Revisions

BACKGROUND

Instability remains the most common complication after revision total hip arthroplasty (THA) and presents a unique treatment dilemma for the orthopedic surgeon. Dual mobility (DM) bearing articulations have been used in France since the 1970s, but have only become more widely adopted in the United States over the last decade. The purpose of this symposium was to discuss the role for DM bearings in revision THA.

METHODS

We reviewed the existing literature on outcomes after DM bearing articulations in revision THA. We also report several case examples of the use of DM in difficult revision THA cases, including acetabular bone loss, failed constrained liner, and adverse local tissue reaction. Finally, we briefly discuss the limitations associated with the use of DM.

RESULTS

Several large retrospective series demonstrate that DM bearings reduce the incidence of dislocation after revision THA when compared with conventional single bearing THA. Specific complications related to DM bearings including polyethylene wear, loosening, intraprosthetic dislocation, and corrosion remain a concern, but appear to have drastically improved over time with modern implant designs.

CONCLUSION

Contemporary DM designs have been established as an effective bearing option to reduce instability in revision THA, although concerns do exist. High-quality prospective studies are necessary to further define the role this bearing option has in the coming years.

Use of a modular hip dual-mobility articulation in patients with high risk of dislocation: a relatively small-sized acetabulum in Asian patients may limit its use

BACKGROUND

Dual-mobility hip component is widely used in Europe and North America, because it effectively reduces hip dislocation in primary and revision total hip arthroplasties. However, reports were limited on the use of dual-mobility articulation in Asian populations.

PURPOSE

The aim of this retrospective study was to review the use of modular dual-mobility hip articulation in Asian patients with the high risk factor for hip dislocation. We also discussed the potential concern on the use of dual-mobility articulation in Asian patients.

METHODS

From Jan 2018 to June 2019, 17 patients were included in this study. The mean age of the patients was (73.8 ± 9.5) years (range: 57-88 years). The mean size of acetabular cup and modular DM liner were (49.5 ± 3.4) mm (range, 46-58 mm) and (40.7 ± 3.4) mm (range, 38-48 mm), respectively. The mean follow-up period was (15.8 ± 3.9) months (range, 11-24 months). The primary outcome was the rate of hip dislocation. The secondary outcomes included the Harris Hip Score. Differences were considered statistically significant at p < 0.05.

RESULTS

Hip dislocation, loosening, peri-prosthetic fractures, or intra-prosthetic dislocation was not found in the series. The mean preoperative and postoperative Harris Hip Scores were 42.2 ± 17.2 (range, 15-80) and 74.7 ± 13.5 (range, 52-97), respectively, giving a mean improvement of 32.5 ± 17.2 (range, 4-72). The improvement was statistically significant (p < 0.05).

CONCLUSIONS

In Asian patients with high risk of hip dislocation, the use of modular dual-mobility hip component produces promising outcomes without hip dislocation, but the relatively small-sized acetabulum may limit it widespread application in other populations worldwide.

TRIAL REGISTRATION

HKUCTR-2913 .

Dual mobility THR: Resolving instability and providing near normal range of movement

BACKGROUND

Dislocation is a common complication of Total Hip Replacement (THR), particularly when performed in primary (indications with increased risk of instability) and in revision scenarios. Dual mobility THR (DMTHR) minimizes the risk of instability in such scenarios, however most of the evidence is from western literature. Results of DMTHR in Indian scenarios where patient want to go back to their normal routine activities of squatting and sitting cross-legged is lacking. The aim of our study was to evaluate the short to mid-term results of DMTHR for varied indications (both primary and revision) in Indian scenario. To evaluate the outcome of the DMTHR in terms of functional range of motion and the ability to go back to their pre-injury level of activity.

METHODS

This is a retrospective study of 150 patients operated with DMTHR between January 2015 to February 2019 with a minimum follow-up of 12 months. Patients were evaluated clinically using Modified Harris Hip Score (HHS), Range of Motion (ROM), and Patient Reported Outcome Measures (PROM) like ability to squat and sit cross legged. Radiological evaluation was done using radiographs to assess loosening, stress shielding, osteolysis.

RESULTS

Mean follow up in our study was 25.2 months (Range 12-46 months). Mean Modified HHS was 71.8 ± 8.11 at 6 weeks post-op and 85.8 ± 7.62 at last follow-up. HHS showed excellent outcome in 36 hips (26.7%), good outcome in 76 hips (56.7%), fair outcome in 20 hips (14.6%), poor outcome in 3 hips (2%). All our patients were allowed to squat and sit cross-legged at a mean follow-up period of 13 weeks (8 weeks-20 weeks) except 10 cases of Revision THR where patients were advised not to squat or sit cross-legged. All patients were able to resume their activities of daily living.

CONCLUSION

DMTHR in patients of all ages has shown a good short to midterm clinical outcome which is comparable to conventional THR. It confers the benefit of stability allowing our patients to squat and sit cross legged which is often one of the expectation and requirement of a patient undergoing THR in India. DMTHR in both primary and revision scenarios exhibit a low risk of dislocation, complications and revision surgery.

Trends in the use of dual mobility bearings in hip arthroplasty

Aims

Dual mobility (DM) bearings are an attractive treatment option to obtain hip stability during challenging primary and revision total hip arthroplasty (THA) cases. The purpose of this study was to analyze data submitted to the American Joint Replacement Registry (AJRR) to characterize utilization trends of DM bearings in the USA.

Methods

All primary and revision THA procedures reported to AJRR from 2012 to 2018 were analyzed. Patients of all ages were included and subdivided into DM and traditional bearing surface cohorts. Patient demographics, geographical region, hospital size, and teaching affiliation were assessed. Associations were determined by chi-squared analysis and logistic regression was performed to assess outcome variables.

Results

A total of 406,900 primary and 34,745 revision THAs were identified, of which 35,455 (8.7%) and 8,031 (23.1%) received DM implants respectively. For primary THA, DM usage increased from 6.7% in 2012 to 12.0% in 2018. Among revision THA, DM use increased from 19.5% in 2012 to 30.6% in 2018. Patients < 50 years of age had the highest rates of DM implantation in every year examined. For each year of increase in age, there was a 0.4% decrease in the rate of DM utilization (odds ratio (OR) 0.996 (95% confidence interval (CI) 0.995 to 0.997); p < 0.001). Females were more likely to receive a DM implant compared to males (OR 1.077 (95% CI 1.054 to 1.100); p < 0.001). Major teaching institutions and smaller hospitals were associated with higher rates of utilization. DM articulations were used more commonly for dysplasia compared with osteoarthritis (OR 2.448 (95% CI 2.032 to 2.949); p < 0.001) during primary THA and for instability (OR 3.130 (95% CI 2.751 to 3.562) vs poly-wear; p < 0.001) in the revision setting.

Conclusion

DM articulations showed a marked increase in utilization during the period examined. Younger patient age, female sex, and hospital characteristics such as teaching status, smaller size, and geographical location were associated with increased utilization. DM articulations were used more frequently for primary THA in patients with dysplasia and for revision THA in patients being treated for instability. Cite this article: Bone Joint J 2020;102-B(7 Supple B):27–32.

Can dual mobility cups prevent dislocation without increasing revision rates in primary total hip arthroplasty? A systematic review

BACKGROUND

Dislocation is one of the leading causes for early revision surgery after total hip arthroplasty (THA). To address this problem, the dual mobility (DM) cup was developed in the 1970s by the French. Despite the increased and, in some countries, broad use of DM cups, high quality evidence of their effectiveness compared to traditional unipolar (UP) cups is lacking. There are a few well-conducted literature reviews, but the level of evidence of the included studies was moderate to low and the rates of revision were not specifically investigated. Therefore, we did a systematic review to investigate whether there is a difference in the rate of dislocations and revisions after primary THA with a DM cup or a UP cup.

METHODS

We conducted a systematic literature search in PubMed, Embase and Cochrane databases in July 2019. The articles were selected based upon their quality, relevance and measurement of the predictive factor. We used the MINORS criteria to determine the methodological quality of all studies.

RESULTS

The initial search resulted in 702 citations. After application of the inclusion and exclusion criteria, eight articles met our eligibility criteria and were graded. Included studies were of medium to low methodological quality with a mean score of 14/24 (11-16) points following the MINORS criteria. In the case-control studies, a total of 549 DM cups and 649 UP cups were included. In the registry studies, a total of 5.935 DM cups and 217.362 UP cups were included. In the case-control studies, one (0.2%) dislocation was reported for the DM cups and 46 (7.1%) for the UP cup (p=0.009, IQR=0.00-7.00). Nine (1.6%) revisions, of which zero due to dislocation, were reported for the DM cup and 39 (6.0%), of which 30 due to dislocation, for the UP cup (p=0.046, CI=-16.93-5.73). In the registry studies 161 (2.7%) revisions were reported for the DM cup, of which 14 (8.7%) due to dislocation. For the UP cup, 3.332 (1.5%) revisions were reported (p=0.275, IQR=41.00-866.25), of which 1.093 (32.8%) due to dislocation (p=0.050, IQR=3.50-293.25).

CONCLUSION

This review suggests lower rates of dislocation and lower rates of revision for dislocation in favor of the DM cups. Concluding, DM cups might be an effective solution to reduce dislocation in primary THA. To evaluate the efficacy of DM cups compared to UP cups, an economic evaluation alongside a randomized controlled trial is needed focusing on patient important endpoints.

LEVEL OF EVIDENCE

III, systematic review of level III studies.

No Difference in Force Required for Intraprosthetic Dislocation of Mixed Manufacturer vs Same Manufacturer Dual Mobility Articulations

BACKGROUND

To avoid the morbidity of removing well-fixed implants during revision surgery, the off-label practice of mixing femoral heads with dual mobility (DM) polyethylene liners from different manufacturers is commonly performed. The resistance to intraprosthetic dislocation, when the inner prosthetic head disengages from the polyethylene bearing, between mixed and same manufacturer constructs remains unknown.

METHODS

Between January 2010 and July 2018, 168 DM liners were retrieved. Specimens were excluded for catastrophic wear (n = 14), previously levered-out (n = 17), and cases in legal proceedings (n = 8). Using a validated setup, 129 specimens were uniaxially loaded 100 mm from the femoral head until lever-out failure of the head from the liner. The difference in maximum lever-out force (LOF) was compared for same and mixed manufacturer retrievals (Student t-test). Multivariable regression analysis evaluated the influence of potential confounders (length of implantation, head size, head material, presence of skirt) on LOF.

RESULTS

Ninety-seven same and 32 mixed manufacturer DM constructs were tested. The average LOF for same (272.6 ± 68.7 N) and mixed (299.2 ± 89.0 N) manufacturer specimens was not significantly different (P = .08). An inner head size of 22.2 mm was associated with 184.4-N increase in LOF (P < .001), the presence of a skirt was associated with 63.8-N increase in maximum LOF, and head material (ceramic vs metal) did not influence LOF.

CONCLUSION

We found no difference in the force required to lever-out same and mixed manufacturer inner heads from DM liners, suggesting that mixing manufacturers when placing DM articulations on well-fixed femoral stems should not increase the risk of intraprosthetic instability.

Is Isolated Mobile Component Exchange an Option in the Management of Intraprosthetic Dislocation of a Dual Mobility Cup?

BACKGROUND

Intraprosthetic dislocation is a specific complication of dual mobility cups, although it occurs less frequently with the latest generations of implants. Intraprosthetic dislocation is related to long-term polyethylene wear of the mobile component chamfer and retentive area, leading to a snap-out of the femoral head. With the increased use of dual mobility cups, even in younger and active patients, the management of intraprosthetic dislocation should be defined according to its type. However, no previous studies, except for case reports, have described the strategy to manage long-term wear-related intraprosthetic dislocation, particularly when a dual mobility cup is not loose.

QUESTIONS/PURPOSES

This study aimed to (1) determine the prevalence of intraprosthetic dislocation in this patient population and the macroscopic findings at the time of surgical revision and (2) evaluate whether isolated mobile component exchange could be an option to manage intraprosthetic dislocation occurring with a well-fixed dual mobility cup metal shell.

METHODS

From January 1991 to December 2009, a continuous series of 5274 THAs with dual mobility cups (4546 patients; 2773 women; mean [range] age 58 years [22-87]; bilateral THA = 728) were prospectively enrolled in our institutional total joint registry. A cementless, hemispherical dual mobility cup was systematically implanted, regardless of the patient's age or indication for THA. At the latest follow-up examination, the registry was queried to isolate each occurrence of intraprosthetic dislocation, which was retrospectively analyzed regarding the patient's demographics, indication for THA, radiographs, intraoperative findings (polyethylene wear and lesion patterns on the mobile component, periarticular metallosis, and implant damage because of intraprosthetic impingement of the femoral neck), management of intraprosthetic dislocation (isolated exchange of the mobile component or revision of the dual mobility cup), and outcome.

RESULTS

At a mean (range) follow-up duration of 14 years (3-26), 3% of intraprosthetic dislocations (169 of 5274) were reported, with a mean (range) time from THA of 18 years (13-22). Intraprosthetic dislocation occurred predominantly in younger men (mean [range] age at THA, 42 years [22-64] versus 61 years [46-87]; p < 0.001, and sex ratio (male to female, 1:32 [96 male and 73 female] versus 0.62 [1677 male and 2700 female]; p < 0.001) in patients with intraprosthetic dislocation and those without, respectively, but was not influenced by the indication for THA (105 patients with intraprosthetic dislocation who underwent THA for primary hip osteoarthritis and 64 with other diagnoses versus 3146 patients without who underwent THA for primary hip osteoarthritis and 1959 for other diagnoses (p = 0.9)). In all patients with intraprosthetic dislocation, a macroscopic analysis of the explanted mobile component revealed circumferential polyethylene wear and damage to the chamfer and retentive area, with subsequent loss of retaining power for the femoral head. Nine percent of intraprosthetic dislocations (16 of 169 patients with intraprosthetic dislocations) were associated with aseptic loosening of the dual mobility cup and were managed with acetabular revision without recurrence at a mean (range) follow-up duration of 7.5 years (5-11). Ninety-one percent of intraprosthetic dislocations (153 of 169) were pure, related to wear of the mobile component chamfer and retentive area without aseptic loosening of the dual mobility cup, and managed with isolated mobile component exchange. Intraprosthetic dislocation recurred in 6% (nine of 153) at a mean (range) follow-up interval of 3 years (2-4.5). Additionally, severe premature polyethylene wear of the mobile component with loosening of the dual mobility cup occurred in 12% of patients (19 of 153) at a mean (range) follow-up duration of 1.5 years (0.5-3).

CONCLUSIONS

A failure rate of 18% (28 of 153 patients undergoing isolated mobile component exchange) was reported within 5 years after isolated mobile component exchange to manage intraprosthetic dislocation occurring with a well-fixed dual mobility cup metal shell. The two modes of failure were early recurrence of intraprosthetic dislocation or severe premature metallosis-related polyethylene wear of the mobile component with loosening of the dual mobility cup. Acetabular revision with synovectomy should remain the standard procedure to manage intraprosthetic dislocation, particularly if periarticular metallosis is present. The exception is intraprosthetic dislocation occurring in elderly or frail patients, for whom a conventional acetabular revision procedure would be associated with an unjustified surgical or anesthetic risk.

LEVEL OF EVIDENCE

Level II, prognostic study.

Dual mobility in primary total hip arthroplasty: current concepts

Total hip arthroplasty (THA) is one of the most successful surgical procedures – reducing pain and providing functional improvement. However, THA instability is a disabling condition and remains the most common indication for revision THA. To combat the risk of instability, the concept of dual mobility (DM) was developed. This article provides a comprehensive review of DM in the literature.

Widespread use of first-generation DM was limited due to concern regarding wear of the polyethylene head and the unique complication of intraprosthetic dislocation (IPD). Implant modifications using highly cross-linked, durable polyethylene and a smooth, cylindrical femoral neck have all but eliminated IPD in contemporary DM.

In multiple studies, DM demonstrates statistically significant reductions in dislocation rates comparative to standard bearing primary THA. These results have been particular promising in high-risk patient populations and femoral neck fractures – where low dislocation rates and improved functional outcomes are a recurrent theme. From an economic perspective, DM is equally exciting – with lower accrued costs and higher accrued utility comparative to standard bearing THA.

Longer-term clinical evidence and higher-quality prospective comparative studies are required to strengthen current research. Dual mobility may well represent the future gold standard for THA in high-risk patient populations and femoral neck fractures, but due diligence of long-term performance is needed before recommendations for widespread use can be justified.

Cite this article: EFORT Open Rev 2019;4:640-646. DOI: 10.1302/2058-5241.4.180089

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

Is a modular dual mobility acetabulum a viable option for the young, active total hip arthroplasty patient?

AIMS

Modular dual mobility (DM) prostheses in which a cobalt-chromium liner is inserted into a titanium acetabular shell ( vs a monoblock acetabular component) have the advantage of allowing supplementary screw fixation, but the potential for corrosion between the liner and acetabulum has raised concerns. While DM prostheses have shown improved stability in patients deemed 'high-risk' for dislocation undergoing total hip arthroplasty (THA), their performance in young, active patients has not been reported. This study's purpose was to assess clinical outcomes, metal ion levels, and periprosthetic femoral bone mineral density (BMD) in young, active patients receiving a modular DM acetabulum and recently introduced titanium, proximally coated, tapered femoral stem design.

PATIENTS AND METHODS

This was a prospective study of patients between 18 and 65 years of age, with a body mass index (BMI) < 35 kg/m² and University of California at Los Angeles (UCLA) activity score > 6, who received a modular cobalt-chromium acetabular liner, highly crosslinked polyethylene mobile bearing, and cementless titanium femoral stem for their primary THA. Patients with a history of renal disease and metal hardware elsewhere in the body were excluded. A total of 43 patients (30 male, 13 female; mean age 52.6 years (sd 6.5)) were enrolled. All patients had a minimum of two years' clinical follow-up. Patient-reported outcome measures, whole blood metal ion levels (ug/l), and periprosthetic femoral BMD were measured at baseline, as well as at one and two years postoperatively. Power analysis indicated 40 patients necessary to demonstrate a five-fold increase in cobalt levels from baseline (alpha = 0.05, beta = 0.80). A mixed model with repeated measures was used for statistical analysis.

RESULTS

Mean Harris Hip Scores improved from 54.1 (sd 20.5) to 91.2 (sd 10.8) at two years postoperatively (p < 0.001). All patients had radiologically well-fixed components, no patients experienced any instability, and no patients required any further intervention. Mean cobalt levels increased from 0.065 ug/l (sd 0.03) preoperatively to 0.30 ug/l (sd 0.51) at one year postoperatively (p = 0.01) but decreased at two years postoperatively to 0.16 ug/l (sd 0.23; p = 0.2). Four patients (9.3%) had a cobalt level outside the reference range (0.03 ug/l to 0.29 ug/l) at two years postoperatively, with values from 0.32 ug/l to 0.94 ug/l. The mean femoral BMD ratio was maintained in Gruen zones 2 to 7 at both one and two years postoperatively using this stem design. At two years postoperatively, mean BMD in the medial calcar was 101.5% of the baseline value.

CONCLUSION

Use of a modular DM prosthesis and cementless, tapered femoral stem has shown encouraging results in young, active patients undergoing primary THA. Elevation in mean cobalt levels and the presence of four patients outside the reference range at two years postoperatively demonstrates the necessity of continued surveillance in this cohort. Cite this article: Bone Joint J 2019;101-B:365-371.

Catastrophic failure of a dual mobility bearing in a revision total hip arthroplasty

The following case demonstrates an example of a catastrophic failure of a dual mobility (DM) bearing used in the setting of a revision total hip arthroplasty for an acetabular component with an excessive abduction angle. Currently, in the literature, it has been demonstrated that DM bearings have decreased polyethylene wear at abduction angles up to 65°; however, this has only been shown in in vitro studies. To our knowledge, there have been no reports of in vivo DM bearings that have demonstrated these same results. In this case, a DM bearing was used in a revision surgery with a retained acetabular component that had an abduction angle of approximately 70°-75° which ultimately led to catastrophic polyethylene failure.

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.

Intraprosthetic dislocation of dual mobility total hip arthroplasty: still occurring?

PURPOSE

The objective was to identify predictive factors for intraprosthetic dislocation (IPD) and to understand how improvements in dual mobility cups (DMC) have helped to reduce dramatically the occurrence of this complication.

METHODS

DM mobile inserts retrieved from 93 hips were divided into three groups: first-generation DMC with IPD ("firstDMC-IPD"), first-generation DMC with over 15 years of implantation without IPD ("firstDMC-noIPD"), and latest-generation DMC ("newDMC"). The predictive factors for IPD based on clinical, prosthetic, radiological and intraoperative characteristics were analysed by multivariate analysis. The surface of each retrieved mobile insert was analysed using three-dimensional CT scan in order to compare their rim wear.

RESULTS

Three predictive factors for IPD were found: a high BMI, a wide rough stem neck and a large cup size. Wear of the firstDMC-noIPD inserts was significantly less than those of firstDMC-IPD inserts and significantly more than those of newDMC inserts. For the firstDMC-IPD inserts, the rim's outer surface wear was significantly greater than the rim's inner surface wear.

CONCLUSIONS

IPD is a specific complication related to wear of the DM mobile insert due to failure of the liner's retaining rim, especially from the rim's outer surface. This long-term issue is different to the early traumatic complication, which can happen after an attempt at closed reduction of a DM THA dislocation. Recent modifications in the design and the coating of contemporary DMC and femoral stems, as well as improvements in the mobile insert itself, seem to corroborate our assumptions about the IPD mechanism and contribute to the quasi-disappearance of this complication.

Comprehensive Review of Current Constraining Devices in Total Hip Arthroplasty

Hip instability after total joint arthroplasty is a devastating complication. Appropriate management of instability is a challenge. Three components that are commonly used in these challenging scenarios are constrained liners, constrained tripolar components, and nonconstrained tripolar components. The biomaterials and biomechanics of these devices vary. Surgeons must take into account the risks associated with each of these components and some surgical pearls for their use. A thorough review of the recent literature allows comparison of results addressing the short-, medium-, and long-term survival of each component. Constraining devices are a good option when used in salvage procedures in elderly and/or low-demand patients with hip instability. However, constraining devices should not be used to correct deficiencies in surgical technique or implant placement.

Salvage of a monoblock metal-on-metal cup using a dual mobility liner: a two-year MRI follow-up study

PURPOSE

Revision of failed modular metal-on-metal total hip replacement (MoM-THA) can be technically difficult. A dual mobility liner can help to salvage a well-fixed acetabular component. The present paper reports the clinical and radiographic outcome of revision of failed Birmingham modular MoM-THA using a dual mobility liner.

METHODS

The present study reports on ten patients (3 female and 7 male) with 11 revision THAs. Patients underwent revision an average of 51 months (range 40-73 months) after index procedure. Mean follow-up after the revision was 31 months (range 24-37 months) and all patients underwent an MRI with metal artifact reduction software (MARS) at least two years after revision to assess for local polyethylene wear and osteolysis.

RESULTS

The Harris Hip score improved from 92.2 (range 63.0-100.0) to 100.0 (p = 0.072). One patient had a one-time dislocation within seven days of surgery. No patient required additional surgeries. Radiographs showed no signs of component loosening and osteolysis and MRI imaging revealed no evidence of polyethylene wear or osteolysis.

CONCLUSION

A dual mobility liner in an existing Birmingham cup can provide excellent clinical and radiological short-term results without MRI evidence of increased polyethylene wear. Post-operative hip precautions should be enforced.

Metal Ion Levels in Young, Active Patients Receiving a Modular, Dual Mobility Total Hip Arthroplasty

BACKGROUND

Dual mobility total hip arthroplasty (THA) components improve stability, yet use of a modular cobalt alloy acetabular liner may be associated with metal ion release. This study's purpose was to measure blood metal ion levels in young, active patients receiving a dual mobility THA prosthesis.

METHODS

This is a prospective study of young, active patients undergoing primary THA. Twenty-six patients received a 22-mm cobalt alloy (n = 10) or a 28-mm ceramic (n = 16) femoral head, a modular cobalt chrome acetabular liner, with a highly cross-linked polyethylene insert (dual mobility). Seventeen control patients received a 32-mm cobalt alloy (n = 6), oxidized zirconium (n = 5), or ceramic (n = 6) femoral head and polyethylene acetabular liner (conventional). All patients received a cementless, titanium femoral stem. Blood metal ion levels (μg/L) were measured preoperatively and at 1 year postoperatively.

RESULTS

No difference was present for age or body mass index (P = .5 and .9). At 1 year postoperatively, mean cobalt levels were greater in the dual mobility cohort (0.23 ± 0.39 vs 0.15 ± 0.07, P < .001). Four patients in the dual mobility cohort had a cobalt level outside the reference range (0.03-0.29), with values from 0.34 to 1.81 μg/L. One patient in the conventional cohort had a cobalt level outside the reference range with a value of 0.39 μg/L.

CONCLUSION

The presence and clinical significance of increased cobalt levels in 4 patients with the use of a modular dual mobility prosthesis demonstrates the necessity of continued surveillance.

Constrained liners, dual mobility or large diameter heads to avoid dislocation in THA

Dislocation remains a common cause of failure after total hip arthroplasty. The limitations of existing approaches to address instability have led to the development of powerfull options: constrained liners, dual mobility and large heads. These implant-related options have proven to be very efficient, but have raised concerns.With constrained liners, restricted range of motion (ROM) is responsible for impingement leading to high likelihood of failure, depending on the design, with various failure modes.Improvements of the bearing materials have addressed some of the concerns about increased volumetric wear of conventional polyethylene and offer an option to reduce instability: large diameter heads have the advantage of increased ROM before impingement, increased head-neck ratio, and jump distance. Highly cross-linked polyethylene helps address the risk for increased wear, and also large heads provide improved stability without the risk of mechanical failures observed with constrained liners. However, the increase of the head size remains limited as reducing the thickness of the liner may lead to fractures. In addition, the jump distance decreases as the cup abduction increases.The dual mobility concept simultaneously attempts to address head-neck ratio, constraint, and jump distance. Despite the need for longer follow-up, concerns raised about potential increased wear and intra-prosthetic dislocation with first generation implants have been addressed with modern designs.With a dramatic increase of the head-neck ratio whilst reducing the risk of mechanical failure or excessive wear, dual mobility THA outperforms large diameter heads and constrained liners at 10 years follow-up. For these reasons, dual mobility continues to gain interest worldwide and is becoming the most popular option to manage instability. Cite this article: Guyen O. Constrained liners, dual mobility or large diameter heads to avoid dislocation in THA. EFORT Open Rev 2016;1:197-204. DOI: 10.1302/2058-5241.1.000054.

Fretting and Corrosion at the Backside of Modular Cobalt Chromium Acetabular Inserts: A Retrieval Analysis

BACKGROUND

Adverse local tissue reaction formation has been suggested to occur with the Modular Dual Mobility (MDM) acetabular design. Few reports in the literature have evaluated fretting and corrosion damage between the acetabular shell and modular metal inserts in this modular system. We evaluated a series of 18 retrieved cobalt chromium MDM inserts for evidence of fretting and corrosion.

METHODS

We assessed the backsides of 18 MDM components for evidence of fretting and corrosion in polar and taper regions based on previously established methods. We collected and assessed 30 similarly designed modular inserts retrieved from metal-on-metal (MoM) total hip arthroplasties as a control.

RESULTS

No specific pattern of fretting or corrosion was identified on the MDM inserts. Both fretting and corrosion were significantly greater in the MoM cohort than the MDM cohort, driven by higher fretting and corrosion scores in the engaged taper region of the MoM inserts.

CONCLUSION

MoM components demonstrated more fretting and corrosion than MDM designs, specifically at the taper region, likely driven by differences in the taper engagement mechanism and geometry among the insert designs. The lack of significant fretting and corrosion observed in the MDM inserts are inconsistent with recent claims that this interface may produce clinically significant metallosis and adverse local tissue reactions.

Dislocation following total hip arthroplasty using dual mobility acetabular components: a systematic review

AIMS

The aim of this systematic review was to report the rate of dislocation following the use of dual mobility (DM) acetabular components in primary and revision total hip arthroplasty (THA).

MATERIALS AND METHODS

A systematic review of the literature according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines was performed. A comprehensive search of Pubmed/Medline, Cochrane Library and Embase (Scopus) was conducted for English articles between January 1974 and March 2016 using various combinations of the keywords "dual mobility", "dual-mobility", "tripolar", "double-mobility", "double mobility", "hip", "cup", "socket". The following data were extracted by two investigators independently: demographics, whether the operation was a primary or revision THA, length of follow-up, the design of the components, diameter of the femoral head, and type of fixation of the acetabular component.

RESULTS

In all, 59 articles met our inclusion criteria. These included a total of 17 908 THAs which were divided into two groups: studies dealing with DM components in primary THA and those dealing with these components in revision THA. The mean rate of dislocation was 0.9% in the primary THA group, and 3.0% in the revision THA group. The mean rate of intraprosthetic dislocation was 0.7% in primary and 1.3% in revision THAs.

CONCLUSION

Based on the current data, the use of DM acetabular components are effective in minimising the risk of instability after both primary and revision THA. This benefit must be balanced against continuing concerns about the additional modularity, and the new mode of failure of intraprosthetic dislocation. Longer term studies are needed to assess the function of these newer materials compared with previous generations. Cite this article: Bone Joint J 2017;99-B(1 Supple A):18-24.

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.

Equivalent wear performance of dual mobility bearing compared with standard bearing in total hip arthroplasty: in vitro study

PURPOSE

Osteolysis in total hip arthroplasty (THA) depends on polyethylene wear and dictates the survival of the prosthesis. Dual mobility in THAs, which is claimed to reduce dislocation risk, has very good long-term clinical results. However, little is known about how the liner wears in this design, compared to the standard single mobility model.

METHODS

A comparative study looking at wear of a conventional ultra-high-molecular-weight polyethylene liner, using gravimetric measurement, between dual mobility implants and standard implants, was performed on a simulator in accordance with a normed protocol based on the same dimensions, environmental conditions and stresses. A linear regression test was employed.

RESULTS

Under the same conditions (loading, cycles, sterilization, material and surface roughness), the gravimetric wear (for conventional polyethylene) is comparable between a standard and a dual mobility cup. This correlates to ten year follow-up results of dual mobility cup.

DISCUSSION - CONCLUSION

This in vitro equivalent wear serves to confirm the very good long-term clinical results observed with dual mobility bearing, whose use should not be restricted by concerns about increased polyethylene wear.

Highly crosslinked polyethylene: a safe alternative to conventional polyethylene for dual mobility cup mobile component. A biomechanical validation

PURPOSE

Dual mobility cup (DMC) consists of a cobalt-chromium (CoCr) alloy cup articulated with a polyethylene (PE) mobile component capturing the femoral head in force using a snap-fit technique. This biomechanical study was the first to evaluate and compare the generation of cracks in the retentive area of DMC mobile components made of highly crosslinked PE (XLPE) or conventional ultra-high molecular weight PE (UHMWPE).

METHODS

Eighty mobile components designed for a 52-mm diameter Symbol® DMC (Dedienne Santé, Mauguio, France) and a 28-mm diameter femoral head were analyzed. Four groups of 20 mobile components were constituted according to the PE material: raw UHMWPE, sterilized UHMWPE, annealed XLPE and remelted XLPE. Ten mobile components in each group were impacted with a 28-mm diameter CoCr femoral head using a snap-fit technique. The occurrence, location and area of the cracks in the retentive area were investigated using micro-CT (Skyscan 1176®, Bruker, Aarsellar, Belgium) with a 35 μm nominal isotropic voxel size by two observers blinded to the PE material and impaction or not of the mobile components.

RESULTS

Compared to conventional UHMWPE, the femoral head snap-fit did not generate more or wider cracks in the retentive area of annealed or remelted XLPE mobile components.

CONCLUSION

This biomechanical study suggests that XLPE in DMC could be a safe alternative to conventional UHMWPE regarding the generation of cracks in the retentive area related to the femoral head snap-fit.

Assessment of Damage on a Dual Mobility Acetabular System

BACKGROUND

Dual mobility designs were introduced to increase stability and reduce the risk of dislocation, both being common reasons for surgical revision after total hip arthroplasty. The in vivo behavior of dual mobility constructs remains unclear, and to our knowledge, no data have been published describing in vivo surface damage to the polyethylene bearing surfaces.

METHODS

We used surface damage assessed on the inner and outer polyethylene bearing surfaces in 33 short-term retrieved dual mobility liners as evidence of relative motion at the 2 bearings. A lever out test was performed to determine the force required for dislocation of the cobalt-chromium femoral head from the polyethylene liner.

RESULTS

Both bearings showed damage; however, the inner polyethylene bearings had higher damage scores, lower prevalence of remaining machining marks, and higher incidence of concentric wear, all consistent with more motion at the inner polyethylene bearing. The inner polyethylene bearings also had a higher occurrence of embedded titanium debris. The damage sustained in vivo was insufficient to lead to intraprosthetic dislocation in any of the retrieved components. Lever out tests of 12 retrievals had a mean dislocation load of 261 ± 52 N, which was unrelated to the length of implantation.

CONCLUSION

Our short-term retrieval data of 33 highly cross-linked polyethylene dual mobility components suggest that although motion occurs at both bearing articulations, the motion of the femoral head against the inner polyethylene bearing dominates. Although damage was not severe enough to lead to intraprosthetic dislocation, failure may occur long term and should be assessed in future studies.

Analysis of Dual Mobility Liner Rim Damage Using Retrieved Components and Cadaver Models

BACKGROUND

The objective of this study was to assess the retentive rim of retrieved dual mobility liners for visible evidence of deformation from femoral neck contact and to use cadaver models to determine if anterior soft tissue impingement could contribute to such deformation.

METHODS

Fifteen surgically retrieved polyethylene liners were assessed for evidence of rim deformation. The average time in vivo was 31.4 months, and all patients were revised for reasons other than intraprosthetic dislocation. Liner interaction with the iliopsoas was studied visually and with fluoroscopy in cadaver specimens using a dual mobility system different than the retrieval study. For fluoroscopic visualization, a metal wire was sutured to the iliopsoas and wires were also embedded into grooves on the outer surface of the liner and the inner head.

RESULTS

All retrievals showed evidence of femoral neck contact. The cadaver experiments showed that liner motion was impeded by impingement with the iliopsoas tendon in low flexion angles. When observing the hip during maximum hyperextension, 0°, 15°, and 30° of flexion, there was noticeable tenting of the iliopsoas caused by impingement with the liner.

CONCLUSION

Liner rim deformation resulting from contact with the femoral neck likely begins during early in vivo function. The presence of deformation is indicative of a mechanism inhibiting mobility of the liner. The cadaver studies showed that liner motion could be impeded because of its impingement with the iliopsoas. Such soft tissue impingement may be one mechanism by which liner motion is routinely inhibited, which can result in load transfer from the neck to the rim.

Reducing the distal profile of dual mobility liners can mitigate soft-tissue impingement and liner entrapment without affecting mechanical performance

Soft-tissue impingement with dual mobility liners can cause anterior hip pain and intra-prosthetic dislocation. The hypothesis of this study was that reducing liner profile below the equator (contoured design) can mitigate soft-tissue impingement without compromising inner-head pull-out resistance and hip joint stability. The interaction of conventional and contoured liners with anterior soft tissues was evaluated in cadaver specimens via visual observation and fluoroscopic imaging. Resistance to inner-head pull-out was evaluated via finite element analyses, and hip joint stability was evaluated by rigid-body mechanics simulation of dislocation in two modes (A, B). Cadaveric experiments showed that distal portion of conventional liners impinge on anterior hip capsule and cause iliopsoas tenting at low flexion angles (≤30°). During hip extension, the rotation imparted to the liner from posterior engagement with femoral neck was impeded by anterior soft-tissue impingement. The iliopsoas tenting was significantly reduced with contoured liners (p ≤ 0.04). Additionally, the contoured and conventional liners had identical inner-head pull-out resistance (901 N vs. 909 N), jump distance (9.4 mm mode-A, 11.7 mm mode-B) and impingement-free range of motion (47° mode-A, 29° mode-B). Thus, soft-tissue impingement with conventional dual mobility liners may be mitigated by reducing liner profile below the equator, without affecting mechanical performance. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:889-897, 2016.

Serum Metal Ion Levels Following Total Hip Arthroplasty With Modular Dual Mobility Components

Dual mobility acetabular components can reduce the incidence of total hip arthroplasty (THA) instability. Modular dual mobility (MDM) components facilitate acetabular component implantation. However, corrosion can occur at modular junctions. Serum cobalt and chromium levels and Oxford scores were obtained at minimum two year follow-up for 100 consecutive patients who had THA with MDM components. Average Oxford score was 43 (range 13-48). Average serum cobalt and chromium values were 0.7 mcg/L (range, 0.0 to 7.0) and 0.6 mcg/L (range, 0.1 to 2.7), respectively. MARS MRI was performed for four patients with pain and elevated serum cobalt levels. Two of these studies were consistent with adverse local tissue reaction. We recommend use of MDM implants in only patients at high risk for dislocation following THA.

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.

Wear testing of total hip replacements under severe conditions

Controlled wear testing of total hip replacements in hip joint simulators is a well-established and powerful method, giving an extensive prediction of the long-term clinical performance. To understand the wear behavior of a bearing and its limits under in vivo conditions, testing scenarios should be designed as physiologically as possible. Currently, the ISO standard protocol 14242 is the most common preclinical testing procedure for total hip replacements, based on a simplified gait cycle for normal walking conditions. However, in recent years, wear patterns have increasingly been observed on retrievals that cannot be replicated by the current standard. The purpose of this study is to review the severe testing conditions that enable the generation of clinically relevant wear rates and phenomena. These conditions include changes in loading and activity, third-body wear, surface topography, edge wear and the role of aging of the bearing materials.

Revision of Failed Hip Resurfacing and Large Metal-on-Metal Total Hip Arthroplasty Using Dual-Mobility Components

Revision of metal-on-metal (MoM) total hip arthroplasty (THA) or hip resurfacing is associated with high complication rates. The authors propose dual-mobility components as a surgical option and present short- to mid-term results of MoM hips revised with dual-mobility components. Eighteen consecutive hips that underwent revision of MoM THA or hip resurfacing using dual-mobility components were identified. At final follow-up (mean, 17.5 months), the visual analog scale, modified Harris Hip Score, and SF-12 scores had all improved (P<.05, P<.01, and P<.05, respectively). There were no dislocations or other complications. Revision of failed MoM THA or hip resurfacing using a dual-mobility device is an effective strategy.

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.

Clinical outcomes, survivorship and adverse events with mobile-bearings versus fixed-bearings in hip arthroplasty-a prospective comparative cohort study of 143 ADM versus 130 trident cups at 2 to 6-year follow-up

The principle of dual mobility cups, often called "tripolar", has been developed to overcome the problem of instability following primary hip arthroplasty. We prospectively compared two cohorts which differed only by the type of bearings, i.e." mobile bearing hip" (MBH) in a 143-study cohort of ADM cups versus "fixed bearing hip" (FBH) of 130 Trident PSL cups, at a follow-up at 2-6years. The survival rates at 4.13-years, with instability as endpoint was significantly (P=0.0176) in favor of mobile bearings at 100% with no dislocation reported, versus 94.8% with fixed bearings. These mobile bearings, matching both "modern" dual mobility cups and annealed highly crossed polyethylene, would appear to offer at longer follow-up a valuable solution to clinical outcomes in acetabular arthroplasty.

Intraprosthetic dislocation of a contemporary dual-mobility design used during conversion THA

Although dual-mobility sockets have been in clinical use for decades in other parts of the world, they recently gained popularity in the United States as an option for primary and revision total hip arthroplasty (THA). Improvements in dual-mobility socket technology include articulation with a metal insert impacted into a metal shell and a femoral head made of highly cross-linked polyethylene. The results and complications associated with the use of dual-mobility sockets employing these technologic advancements are not known. Specifically, intraprosthetic dislocation is a well-known complication of these implants and has been reported extensively in the literature. To the authors' knowledge, its occurrence in a modern dual-mobility socket has not been reported. The authors report a case of early intraprosthetic dislocation of a contemporary dual-mobility design used to convert a patient to THA after failed fixation of intertrochanteric hip fracture. At retrieval, there was evidence that the outer bearing may have ceased moving, causing localized focal impingement of the implant neck on the retentive ring. The authors theorized that external hip impingement (pelvic against trochanter) and previous surgery that led to the formation of scar tissue could have caused the outer bearing surface to cease its motion. This ultimately led to impingement of the femoral component neck on the retentive ring, which led to the intraprosthetic dislocation. Dual-mobility cups provide an attractive option to decrease wear and improve stability. Further research is needed to establish the ideal construct design and materials.