Results of the Evora dual-mobility socket after a minimum follow-up of five years

No dislocation and low complication rate for a modern dual mobility cup with pre-impacted femoral head in primary hip replacement: A consecutive series of 175 hips at minimum 5-year follow-up

INTRODUCTION

Despite its excellent results in preventing dislocation, the dual mobility cup (DMC) is still struggling to be adopted by some teams due to premature wear and loosening reported on first-generation implants. Therefore, this study aimed to assess the mid-term survivorship of a modern DMC with a pre-impacted head and the radio-clinical results at a minimum follow-up of 5 years.

METHODS

This was a retrospective single-centre study performed on patients who had a primary total hip replacement for osteoarthritis in 2016. The cup was a third-generation DMC with a pre-impacted femoral head. Clinical (harris hip score (HHS)) and radiological (cup abduction, anteversion, overhang, and radiolucent lines) results were recorded, as well as complications, particularly dislocations and survivorship. A minimum of five years of follow-ups was required.

RESULTS

One hundred and seventy-five hips (167 patients) met the inclusion criteria. Five hips (2.9%, 5/175) were lost to follow-up and excluded from the postoperative analysis. The mean follow-up period was 70 ± 2.9 months [63.6-76.5]. Three cups needed revision surgery (1.8%, 3/170): one for septic loosening, and two for chronic infection. At 77 months, the global survival probability was 98.2% ± 1, and the survival probability excluding septic aetiology was 100%. There was a significant improvement in the HHS from pre-operatively (48.3 ± 6.0 [14.0-70.0]) to post-operatively (96 ± 4.5 [50-100]) (p < 0.0001). There were no postoperative dislocations recorded, nor any iliopsoas-impingement or symptomatic cam-effect.

DISCUSSION

This study showed excellent survival and good radiological and clinical results of this dual mobility cup at a mid-term follow-up. None of the patients had dislocation or any specific complication feared with dual mobility cups.

Monobloc Dual Mobility With a Minimum 5-Year Follow-Up: A Safe and Effective Solution in Primary Total Hip Arthroplasty

BACKGROUND

Instability constitutes over 20% of revisions after total hip arthroplasty (THA). Dual mobility (DM) designs were introduced as a solution to this problem. However, the few publications that have reported promising results for monobloc DM constructs have been limited by sample size or length of follow-up. The purpose of this study is to evaluate mid-term outcomes (minimum 5-year follow-up) of a single-surgeon series utilizing a monobloc DM acetabular component in patients with high risk for dislocation.

METHODS

This is a single-surgeon consecutive series of 207 primary THAs implanted with a monobloc DM component in patients who were considered at high risk for dislocation. Patient demographics and case-specific data were collected retrospectively. All patients had a minimum of 5-year follow-up. The Mann-Whitney U test was used to assess continuous variables, whereas categorical variables were analyzed using the chi-square test. Survival probability was calculated using the Kaplan-Meier method.

RESULTS

Radiographic analysis did not reveal acetabular radiolucency in any patients, and there were no revisions for aseptic loosening. In addition, there were no dislocations. Seven of 205 patients (3.4%) were revised, 5 on the femoral side due to periprosthetic fracture and the remaining two for infection. Survivorship of the acetabular component from revision was 99%. The mean Veteran RAND (VR-12) physical score improved from 7 (standard deviation [SD]: 13.7) preoperatively to 9.5 (SD: 17.6) at the final follow-up. Similarly, the hip disability osteoarthritis score improved from 8 (SD: 17.9) preoperatively to 21.2 (SD: 37).

CONCLUSION

Monobloc DM components reliably prevent dislocation after primary THA in high-risk patients. At mid-term follow-up, this DM monobloc component demonstrates excellent implant survivorship, radiographic fixation, and improved functional outcomes.

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.

Cemented Dual Mobility Cup for Primary Total Hip Arthroplasty in Elder Patients with High-Risk Instability

Several studies have shown that double mobility (DM) cups reduce postoperative dislocations. Does the cemented dual mobility cup reduce dislocations in a specific cohort of elder patients with a high dislocation risk? Our hypothesis is that this implant is optimal for elder patients because it reduces early dislocation. We have retrospectively reviewed elder patients who underwent total hip arthroplasty (THA) with cemented double mobility cup between March 2009 and January 2018. The inclusion criteria were patients (>75 years) who were operated on for primary THA (osteoarthritis or necrosis) with a cemented dual mobility cup and a high-risk instability (at least two patient-dependent risk factors for instability). The exclusion criteria were revision surgeries or hip fracture. In all the cases, the same surgical approach was performed with a Watson Jones modified approach in supine position. We have collected demographic data, instability risk factors. Patients were classified using the Devane's score, Merle d'Aubigné score and the patient's likelihood of falling with the Morse Fall Scale. Surgical and follow-up complications were collected from their medical history. Sixty-eight arthroplasties (68 patients) were included in the study. The median age was 81.7 years (SD 6.4), and the American Society of Anesthesiologists (ASA) score showed a distribution: II 27.94%, III 63.24% and IV 8.82%. Devane's score was less than five in all of the cases. At least two patient-dependent risk factors for instability (87% had three or more) were present in each case. The median follow-up time was 49.04 months (SD 22.6). Complications observed were two cases of infection and one case of aseptic loosening at 15 months which required revision surgery. We did not observe any prosthetic dislocation. The cemented dual mobility cup is an excellent surgical option on primary total hip arthroplasties for elder patients with high-risk instability.

THA for a Fractured Femoral Neck: Comparing the Revision and Dislocation Rates of Standard-head, Large-head, Dual-mobility, and Constrained Liners

BACKGROUND

THA is a reasonable surgical option for some patients with fragility fractures of the femoral neck, but it has the risk of prosthesis dislocation. The prosthesis combination that reduces the risk of dislocation and the rate of revision surgery is not known.

QUESTIONS/PURPOSES

In patients receiving primary THA for a femoral neck fracture, does (1) the rate of all-cause revision or (2) the reason for revision and rate of revision for dislocation differ among THA with a standard head size, large head size, dual mobility (DM), or constrained liner? (3) Is there a difference in the revision risk when patients are stratified by age at the time of surgery?

METHODS

Data were analyzed for 16,692 THAs performed to treat fractures of the femoral neck reported in the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) from January 2008 to December 2018, as this included the first use of DM prostheses. The AOANJRR includes information on more than 98% of arthroplasty procedures performed in Australia. Most patients were female (72%) and the mean age was 74 years ± 11. There were 8582 standard-head prostheses, 5820 large-head prostheses, 1778 DM prostheses, and 512 constrained prostheses identified. The cumulative percent revision (CPR) was determined for all causes as well as CPR for dislocation. The time to the first revision was described using Kaplan-Meier estimates of survivorship, with right censoring for death or closure of the database at the time of analysis. The unadjusted CPR was estimated each year of the first 10 years for standard heads, 10 years for large heads, 8 years for constrained liners, and 7 years for DM prostheses, with 95% confidence intervals using unadjusted pointwise Greenwood estimates. The results were adjusted for age, sex, femoral fixation, and head size where appropriate and were considered by age groups < 70 and ≥ 70 years.

RESULTS

When adjusted for age, sex, femoral fixation and head size, there was no difference in the rate of all-cause revision at 7 years for any of the four groups. There was no difference in the rate of all-cause revision when patients were stratified by < 70 or ≥ 70 years of age. Dislocation was the most common reason for revision (32%). When analyzing revision for dislocation alone, large-head THA had a lower rate of revision for dislocation compared with standard head (HR 0.6 [95% CI 0.4 to 0.8]; p < 0.001) and DM prostheses had a lower rate of revision for dislocation than standard head for the first 3 months (HR 0.3 [95% CI 0.1 to 0.7]; p < 0.004) but not after this time point.

CONCLUSION

The Australian registry shows that there is no difference in the rate of all-cause revision for standard-head, large-head, DM prostheses or constrained liner THA after femoral neck fractures for all patients or for patients stratified into younger than 70 years and at least 70 years of age groups. Dislocation is the most common cause of revision. Large-head prostheses are associated with a lower revision risk for dislocation and DM prostheses have a lower rate of revision for dislocation than standard heads for the first 3 months only. Surgeons treating a femoral neck fracture with THA might consider a large head size if the diameter of the acetabulum will allow it and a DM prosthesis if a large head size is not possible. The age, life expectancy and level of function of patients with femoral neck fractures minimizes the potential long-term consequences of these prostheses. The lack of significant differences in survival between most prosthesis combinations means surgeons should continue to look for factors beyond head size and prosthesis to minimize dislocation and revision surgery.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Ten- to 16-Year Results of a Modern Cementless Dual-Mobility Acetabular Implant in Primary Total Hip Arthroplasty

BACKGROUND

The purpose of this study is to assess the radiographic results, clinical outcomes, and survivorship of a modern cementless dual-mobility cup (DMC) implant as a primary THA with a minimum of 10 years follow-up.

METHODS

This study retrospectively assessed a series of 310 primary THAs using a modern-generation cementless DMC (Saturne acetabular cup) between April 2001 and December 2005 at a single center. Patients were followed prospectively clinically and radiographically after surgery. Hips with follow-up less than 120 months were excluded from the study (5 lost to follow-up and 167 deceased). In total, a cohort of 138 hips were included for preoperative and postoperative analysis with an average follow-up of 152.4 months. All complications were collected, and a Kaplan-Meier survival analysis was performed.

RESULTS

There was a significant increase in the mean Harris and Postel-Merle d'Aubigne scores between preoperative and postoperative cohorts (P < .001). No loosening of the cup and no acetabular osteolysis were found at final follow-up. No prosthetic dislocation, no intraprosthetic dislocation, and no infections were reported. The survival curve of THA in the total cohort (N = 310) was about 98% at 10 years with 3 stem revisions for femoral fracture. One psoas impingement was also described.

CONCLUSION

This study showed no acetabular component failure and no reported cases of acetabular osteolysis with this DMC acetabular component retention at 10 years. No prosthetic or intraprosthetic dislocation was reported.

Modern Dual-Mobility Cups in Revision Total Hip Arthroplasty: A Systematic Review and Meta-Analysis

BACKGROUND

The purpose of this systematic review is to analyze the outcomes of dual-mobility (DM) cups in revision total hip arthroplasty (THA). Specifically, we evaluated the following: (1) all-cause and aseptic survivorship rates; (2) dislocation rates; (3) complications; and (4) clinical outcomes reported using validated health status measures.

METHODS

A comprehensive literature search included studies that reported the following: (1) re-revision rates, (2) complications, and (3) clinical outcomes following DM use in revision THA. The following exclusion criteria were used: (1) studies that did not stratify their analysis between primary and revision THA, (2) studies that utilized off-label techniques, (3) review articles, (4) case studies, (5) basic science articles, (6) non-English language reports, and (6) reports on patients who underwent surgery before 2010, in order to reflect modern DM implants use and technology. A total of 9 studies were included in our final analysis.

RESULTS

Aseptic and all-cause survivorship rates were 97.7% and 94.5%. Prevalence of dislocation was 2.2%, and 0.3% for intraprosthetic dislocation. Meta-analysis comparing DM to fixed-bearing prostheses demonstrated a significantly lower odds of dislocation in the DM cohort (odds ratio 0.24, P = .002). Complications occurred in 7.4% of revision THAs with DM cups, while infection rates totaled to 3.3% of cases. Studies comparing outcomes using Harris Hip Scores did not demonstrate a statistically significant difference in improved postoperative scores (P > .05).

CONCLUSION

DM cups have demonstrated excellent survivorship, low dislocation, and overall complication rates. Therefore, it can be considered a safe and effective option, particularly in the high-risk patients who undergo revision THA.

Course of dislocated posterior hip arthroplasty: A continuous 232-patient series at a mean 10 years' follow up (range, 1-22 years)

BACKGROUND

Dislocation rates in posterior total hip arthroplasty (THA) range between 2% and 5%, but long-term course (recurrence of dislocation or revision surgery) is not known, most series having short follow-up or small populations. We therefore conducted a retrospective study on a large series, to determine long-term rates of recurrence and surgical revision and recurrence risk factors.

HYPOTHESIS

Long-term follow-up of a large cohort of THA dislocations enables recurrence rate and factors to be determined.

MATERIAL AND METHOD

Five hundred and nine cases of THA dislocation were admitted to our center between 1994 and 2008. A hundred and twenty seven incomplete files and 150 patients who had received their THA elsewhere were excluded, leaving 232 patients: 150 female, 82 male. Mean age at THA (163 primary, 69 revision) was 63 years (range, 15-90 years), and 65 years (range 20-90 years) at first dislocation, with a mean interval to dislocation of 25 months. Minimum follow-up was 8 years up to 2016, or 1 year taking account of deaths (111 deaths). There were 46 anterior, 185 posterior and 1 multidirectional dislocations. The following potential recurrence factors were assessed: gander, age, body-mass index (BMI), etiology, surgical history, bearing diameter and type, component fixation means, dislocation direction, and time to dislocation.

RESULTS

A hundred and thirty three of the 232 patients (57%) showed at least 1 recurrence, at a mean 38 months (range, 0.5-252 months); 78 experienced a second and 32 a third recurrence. Ninety-nine (43%) had only 1 dislocation, without recurrence, but 17 of these (17%) underwent reoperation for other causes. The reoperation rate was 17/232 (7%) excluding recurrent instability, and 84/232 (36%) for instability. Fourty-eight months after the first dislocation, 84/133 cases of recurrence (63%) had been reoperated on: 16 complete replacements, 18 bearing replacements, 42 dual mobility cups, one large diameter cup, seven Lefèvre retentive cups. The rate of revision surgery for instability was high, at 84/232 (36%), and higher again in relation to recurrence (84/133: 63%). Only posterior dislocation emerged as a factor for recurrence (HR=1.774, 95% CI [1.020-3.083]), the other tested factors showing no correlation.14 of the 84 revision surgeries for instability (16.6%) were followed by recurrence, without identifiable risk factors.

CONCLUSION/DISCUSSION

The recurrence rate was 57%, with posterior dislocation as the only risk factor. The rate of revision surgery for recurrence was 84/232 (36%), with 14/84 revision procedures (16.6%) followed by further recurrence.

LEVEL OF EVIDENCE

IV, retrospective, without control group.

Evidence based management of intracapsular neck of femur fractures

Neck of femur fractures are occurring at an increased incidence. Functionally independent patients without cognitive impairment can expect reasonable life expectancy. This indicates the need for a durable surgical option that optimises the chance to return to pre-injury functional status, with minimal risk of complications and reoperation. Most fractures are displaced. Surgical options include internal fixation, hemiarthroplasty or total hip arthroplasty (THA). Evidence is conclusive that arthroplasty options outperform internal fixation in terms of function, quality of life and reoperation rates. In anyone other than young patients where head preserving surgery is required, arthroplasty is the standard of care. Hemiarthroplasty is the heavily favoured arthroplasty option for surgeons. However, in patients other than the extreme elderly, medically infirm, neurologically impaired, or with little or no ambulatory capacity, the evidence to support hemiarthroplasty is lacking. In functionally independent patients without cognitive impairment, THA should be considered the gold standard, producing better functional and quality of life outcomes, lower reoperation rates and better cost effectiveness, with no difference in complications or mortality. An increased risk of dislocation does exist. This may be reduced with modern surgical technique and implant options. Low amounts of research have been afforded to undisplaced fractures. For this fracture type, surgery is the standard of care. Despite a higher risk of reoperation, internal fixation is the preferred option for all age groups. Further study is required to identify the difference between internal fixation and THA, in particular, for unstable fracture patterns in elderly patients.

Dual mobility total hip arthroplasty in hemiplegic patients

Introduction: The rate of cerebrovascular insults is increasing, currently leaving many patients with difficulties to maintain their balance due to muscular weakness and/or poor central control. Those patients are at risk of dislocation when total hip arthroplasty (THA) is planned. Instability remains the most significant issue after primary THA especially in such groups of patients. The risk is more pronounced when other factors are added such as, older age, femoral neck fractures, avascular necrosis and/or hip osteoarthritis. Dual mobility cup (DMC) is considered as a prosthesis with higher inherent stability that may help in such situation. In this patient series, we aimed to evaluate stability, clinical and radiological results of dual mobility THA done on the weak limb of hemiplegic patients.

Methods: Twenty-four consecutive hemiplegic patients have undergone DMC with a mean age of 68 years. The indication for surgery was hip osteoarthritis in one third of the patients and femoral neck fractures in the remaining patients. Those patients were capable of walking prior to hospital admission despite weakness. Those patients were observed postoperatively for at least one year. Clinical results and complications were recorded.

Results: After a minimum of one year, 91.6% of the patients have satisfactory results. No cases of hip or intraprosthetic dislocation were observed.

Discussion: Dual mobility THA in the hemiplegic patients provides both efficacy and stability with good functional results.

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.

[Use of dual mobility cups for revision hip arthroplasty]

The dual mobility cup (DMC) is an increasingly important tool not only in primary but also in revision total hip arthroplasty to prevent dislocation and eventually reduce postoperative complication rates. Various studies have shown survival rates with DMCs of up to 100% with an average dislocation rate of less than 1.5% after primary hip arthroplasty and a follow-up of 10 years. In revision surgery, survival rates of up to 99% were reported with dislocation rates between 0 and 10% after an average of 5 years after implantation. This article is intended to provide an overview of the principle and function of DMCs. Furthermore, indications as well as complications are presented.

The evolution of outcomes and indications for the dual-mobility cup: a systematic review

PURPOSE

Instability following total hip arthroplasty remains a common and disabling complication. The dual mobility cup (DMC) allows a reduction in the dislocation rate. An increasing number of studies have been undertaken to better understand DMC long term outcomes and complications. The goal of this systematic review was to clarify its different uses and outcomes according to the indications.

METHODS

A comprehensive literature review was performed using the keywords 'dual mobility' and 'tripolar cup' with no limit regarding the year of publication. One hundred seventy six publications were identified.

RESULTS

Current literature shows that "contemporary" dual mobility cup are a significant indication to manage instability following primary and revision hip arthroplasty. Survivorship at midterm is comparable to other articulations for primary THA, but is more difficult to evaluate in revision. Intra-prosthetic dislocation, wear, and loosening are now uncommon with new generations of DMC.

CONCLUSIONS

Compared to previous generations of DMC, the current "contemporary" DMC presents a significant improvement. Current literature reveals a tendency to increase the indications but further studies with long term follow up remain important to consolidate these findings.

Do Dual-Mobility Cups Reduce the Risk of Dislocation in Total Hip Arthroplasty for Fractured Neck of Femur in Patients Aged Older Than 75 Years?

BACKGROUND

Total hip arthroplasty (THA) for intracapsular neck of femur (NOF) fracture remains debatable as it is associated with higher rates of dislocation, notably in the older part of the population. We hypothesized this risk could be limited using dual-mobility cups (DMCs).

METHODS

Eighty-two patients (83 hips) aged older than 75 years underwent DMC-THA using a posterolateral approach for an intracapsular NOF fracture.

RESULTS

Clinical data were collected in 45 patients at a mean of 23.8 ± 9.4 months (12.1-42 months). The mortality rates were 19% (16 patients) and 36.5% (30 patients) at 1 year postoperatively and at the last follow-up, respectively. Postoperatively, there were 2 dislocations of the large articulation (4.4%) and one intraprosthetic dislocation (2.2%), all related to technical errors. Functional results were rated at least good in 71% cases, whereas the Parker and Devane scores were stable, indicating optimal restoration of autonomy and physical activity.

CONCLUSION

Although technically demanding, DMC-THA may prevent dislocation in intracapsular NOF fracture in elderly patients, while consistently limiting the risk of loss of independence.

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.

Dual mobility cups in total hip arthroplasty

Total hip arthroplasty (THA) is considered one of the most successful surgical procedures in orthopaedics. With the increase in the number of THAs performed in the world in the next decades, reducing or preventing medical and mechanical complications such as post-operative THA instability will be of paramount importance, particularly in an emerging health care environment based on quality control and patient outcome. Dual mobility acetabular component (also known as unconstrained tripolar implant) was introduced in France at the end of the 1970s as an alternative to standard sockets, to reduce the risk of THA dislocation in patients undergoing primary THA in France. Dual mobility cups have recently gained wider attention in the United States as an alternative option in the prevention and treatment of instability in both primary and revision THA and offer the benefit of increased stability without compromising clinical outcomes and implant longevity. In this article, we review the use of dual mobility cup in total hip arthroplasty in terms of its history, biomechanics, outcomes and complications based on more than 20 years of medical literature.

Are modern dual mobility cups a valuable option in reducing instability after primary hip arthroplasty, even in younger patients?

Hip instability after total hip replacement has been shown to be a critical cause of failure. The use of dual mobility has been classically restricted to patients "at risk", over 70 years of age. The question rises up about extended indications of so-called "modern" second generation dual mobility cups. This prospective multicenter study reports on first results at 2-5 years of the HA anatomical ADM cup upon two comparative groups of patients under 70 years (112 hips) vs. over 70 years of age (325 hips). No dislocation, migration, tilting, wear, or intra-prosthetic dislocation was recorded within each of the two cohorts. Survivorship for cup failures at this 4-year period was ideal at 100% in the younger patients, and 99.7% in the older group of patients.

Femoral head dislodgement complicating use of a dual mobility prosthesis for recurrent instability

The dual mobility cup is an unconstrained tripolar configuration newly introduced to the United States in February 2011. The dual mobility construct allows for a larger femoral head to improve motion and minimize the risk of dislocation. We present a case of a patient who received the dual mobility cup for the treatment of recurrent dislocation following total hip arthroplasty. Early in the patient's postoperative course, the implant failed at the articulation between the larger outer polyethylene head and inner smaller metal femoral head following an attempt at closed reduction. This implant specific complication has not been reported in the North American literature.

Biomechanical concept and clinical outcome of dual mobility cups

Dual mobility cup systems in total hip arthroplasty consist of a metal back with a non-constrained liner, in which a constrained standard head articulates. While superior stability of such implants in comparison with standard total hip replacements is assumed, it is the purpose of this study to outline the biomechanical concept of dual mobility cups and to describe implant survival and dislocation rate based on the series published in the English-speaking and Francophone literature. A growing body of evidence indicates reduced dislocation rates in primary and revision total hip arthroplasty and in selected tumour cases. The limited availability of studies evaluating long-term implant survival and existing concerns with regard to increased wear rates and aseptic loosening, leads to the conclusion that such implants have to be used with prudence, particularly in standard primary hip arthroplasty and in young patients.

Recurrence of dislocation following total hip arthroplasty revision using dual mobility cups was rare in 180 hips followed over 7 years

BACKGROUND

Dual mobility (DM) cups of mobile polyethylene were introduced to prevent total hip arthroplasty (THA) dislocation, but no large series with this design to treat recurrent instability have been reported.

PURPOSE

Our retrospective investigation ascertained the efficiency of DM cups in correction of recurrent dislocation and assessed any adverse effects.

METHODS

One hundred eighty THAs with recurrent instability were revised to DM cups in 180 patients (mean age, 67.4 ± 11.7 years; range, 19 to 92 years). Thirty-one patients (17.2%) underwent at least one earlier THA revision, and 15 (10.3%) incurred non-union of the greater trochanter. Of the initial group in 2009, 145 patients had completed evaluations which included assessment of the Harris Hip Score and a radiographic assessment at a mean follow-up of 7.7 ± 2.2 years (range, 4 to 14 years). The rate of survival was calculated considering any reason for revision as failure.

RESULTS

At follow-up, Harris hip score was 83.9 ± 16.1 (range, 21 to 100). Dislocation of the large articulation occurred in seven hips (4.8%), and only two recurred (1.4%) (one requiring additional revision). In addition, two intra-prosthetic dislocations of the small articulation (1.4%) were observed and needed revision surgery. The large number of earlier surgeries and non-union of the greater trochanter were related to recurrent instability. Two cups (1.4%) showed signs of definite loosening; six (4.1%) presented signs of possible loosening. Twenty-nine hips manifested femoral or acetabular osteolysis (20%), but only three were severe. Eight-year survival rate considering revision for any reason was 92.6% (95% CI, 85.5-96.4%).

CONCLUSIONS

This series indicates that DM cups are a viable option to treat recurrent THA instability. Their design provides a low risk of recurrent instability without increasing mechanical complications.

Acetabular revision using a press-fit dual mobility cup

INTRODUCTION

Dual mobility cups are especially indicated in total hip replacement revision, the risk of recurrent instability being greater than in primary surgery. In revision, however, primary cup fixation is uncertain without routine anchoring screws.

HYPOTHESIS

The stability of dual mobility cups impacted without cement, supplementary screw(s) or anchoring pegs fixation is satisfactory in total hip arthroplasty acetabular component revision, and prevents instability accidents.

PATIENTS AND METHODS

Twenty three patients were operated on by the same surgeon between January 1999 and December 2006 and prospectively followed up to a mean 4 1/2 years (range,2-10 yrs). A Collégia cup (Wright Medical France, Créteil, France) was impacted in 23 total hip arthroplasty acetabular component revisions, including 17 cases of SOFCOT grade-1 bone-stock loss and six of grade 2.

RESULTS

There were six clinically poor results on the Merle D'Aubigné scale. One case of early migration occurred, in a multioperated acetabulum. There was one isolated dislocation and one recurrent dislocation associated with loose greater trochanter nonunion, but tolerated as it was infrequent.

DISCUSSION

This option simplifies revision surgery and limits the risk of dislocation if the abductor muscles unit is continuous. It is indicated when local bone-site compromise encompass a wall-contained cavitary defect at most. A medial wall defect, if moderate, does not in our view preclude using a primary cup, impacted with a certain degree of protrusion. Longer-term follow-up will be needed to confirm these medium-term findings.

LEVEL OF EVIDENCE

Level IV. Prospective non comparative therapeutic study.