Intra-prosthetic dislocation of dual-mobility cups after total hip arthroplasty: potential causes from a clinical and biomechanical perspective

Wear debris in metal-on-metal bearings and modular junctions : What have we learned from the last decades?

Metal-on-metal (MoM) bearing hip arthroplasty saw increasing utilization and peaked in the 1990s and early 2000s. Although the linear and volumetric wear rate for a MoM bearings was lower than its polyethylene counterpart, metal ion particles were found to be approximately 10 × smaller and 500 × higher in quantity compared to polyethylene wear debris. Research into these articulations have demonstrated their relationship to the formation of lymphocyte-mediated adverse local tissue reactions. The work-up for metal particle-associated conditions (metallosis) includes a thorough patient history and physical examination, blood laboratory studies for metal ion concentrations, and advanced imaging studies including magnetic resonance imaging (MRI). The treatment of metallosis and adverse local tissue reactions ranges from close serial observation to extensive debridement and full revision of arthroplasty components, when indicated.

Dual Mobility Total Hip Replacements in Young Patients- A Systematic Review

Background

There is little consensus on outcomes of dual Mobility total hip replacement (DM-THR) in younger patients. We performed a systematic review to examine this.

Methods

A systematic review of all observational studies and randomised controlled trials of patients under 70 with primary DM-THR in MEDLINE, EMBASE, Pubmed, Cochrane was performed according to PRISMA guidelines. Collected data included demographics, revision, dislocation and infection rates and functional scores.

Results

Twelve papers studying 738 DM-THR in 664 patients were included. The mean patient age was 46.9 years (13.5-69.0), with 319 (48.0%) being female and 419 (52.0%) being male. After an average follow-up of 90.0 months (1-371 months), the revision rate was 12.7% (84 hips), 0 dislocations were reported but 2.5% (15 hips) underwent intra-prosthetic dislocation. 32.1% hip revisions were due to aseptic loosening.

Conclusion

Limited literature surrounding the use of DM-THR suggests favourable stability but higher revision rates than conventional THR.

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.

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.

Long-term survival of the Lefèvre retentive cup: 12-year follow-up analysis of 466 consecutive cases

INTRODUCTION

The Lefèvre retentive cup is a salvage solution for total hip replacement at high risk of dislocation. Only a few studies have reported the medium or long-term survival; most often, only a small number of patients were included in these studies. This led us to conduct a retrospective analysis of a large population to determine: 1) the 10-year survival rate after primary or revision arthroplasty, 2) the complication rate.

HYPOTHESIS

The dislocation rate is<5% for revision arthroplasty and<2% for primary arthroplasty.

MATERIAL AND METHODS

This single-center retrospective study included 466 consecutive total hip replacements performed with the Lefèvre retentive cup with a 12-year theoretical minimum follow-up (1/1/1998 to 31/8/2006). There were 257 indications for primary arthroplasty and 209 for revision arthroplasty. The cohort had 316 women and the mean age at surgery was 72.9years (30.2-89.9). The mean follow-up was 10.2±5 years (0.1-19.3). A statistical analysis was done based on the Kaplan-Meier survival curves in two subsets of patients: primary and revision surgery.

RESULTS

At the final review, 264 patients had died because of reasons unrelated to the procedures (mean 7.8±4.7years after the procedure), 48 were lost to follow-up (mean 3.0±3.3years after the procedure), and 39 patients (8%) had undergone acetabular revision of which 12 were for infection (2.5%), 25 were for loosening (5.4%) (5 femoral loosening only) and 2 were for dislocation (0.4%). In all, there were 10/466 dislocations (2.1%) of which 5/257 (1.9%) were in the primary group and 5/209 (2.4%) were in the revision group: 2 had a cup exchange and 8 were reduced by closed procedures. The probability of survival free of mechanical complications at 10years was estimated at 94.8%±1.6% (95% CI: 91.6%-98.0%) for the primary group and 87.8%±2.7% (95% CI: 82.4%-93.2%) for the revision groups (p=0.0017). There were 39 re-operations in the overall cohort: 1/257 (0.4%) for dislocation, 7/257 (2.7%) for aseptic loosening and 3/257 (1.2%) for infection in the primary group, while in the revision group, 1/209 (0.5%) was for dislocation, 18/209 (8.6%) for aseptic loosening and 9/209 (4.3%) for infection.

CONCLUSION

The Lefèvre retentive cup has good long-term survival with a low mechanical complication rate, both in primary and revision surgery. To us, this implant appears to be a reliable salvage procedure for total hip replacement in patients at high risk for dislocation.

LEVEL OF EVIDENCE

IV; retrospective study without control group.

Dual mobility hip arthroplasty: iatrogenic intraprosthetic dislocation of a 22 mm head

We describe the first intraprosthetic dislocations of a 22 mm head in a dual mobility hip replacement in the literature. This case emphasises the importance of information gathering and planning when dealing with arthroplasty complications. Furthermore, it highlights the necessity of adequate muscle relaxation and analgesia when dealing with hip dislocations. A 78-year-old patient presented to the emergency department (ED) with a spontaneous dislocation of her left dual-mobility total hip replacement 3 months after first-stage revision surgery for infection. Reduction via manipulation under analgesia was then attempted in the ED but was ultimately unsuccessful; an iatrogenic intraprosthetic dislocation of the polyethylene liner was sustained. Several factors may have contributed to liner dislocation: a failure to appreciate the implant type, multiple manipulations in ED were attempted under analgesia, but no sedation or muscle relaxation was administered to the patient. The patient subsequently underwent revision surgery.

Clinical Concerns With Dual Mobility- Should I Avoid it When Possible?

The utilization of dual mobility (DM) articulations in total hip arthroplasty (THA) is increasing. The principal appeal of DM implants is its ability to reduce postoperative instability by maximizing the effective ball head size for each reconstruction. However, while DM implants have been used worldwide for over 3 decades, the experience in North America is more limited. Moreover, there remains concerns with intraprosthetic dissociation, wear, metallosis, and soft tissue impingement. Therefore, the purpose of this article is to review the available evidence for these potential issues. First, intraprosthetic dissociation (IPD) is a unique complication of DM implants. Although the rate has decreased with improvements in materials and design, the reported prevalence is approximately 1%. Second, wear in DM implants can be unpredictable and increased wear has been reported in younger, active patients. Third, corrosion in modular DM implants has been described and elevations in serum cobalt and chromium levels have been reported. While the clinical significance of these elevations is unclear, it remains a source of concern with these implants. Finally, psoas impingement and entrapment can be a source of persistent groin pain after THA. DM articulations are a valuable addition to the armamentarium of total hip surgeons. However, these bearings are not free of complications. Consequently, current data only support selective use of DM bearings in patients at increased risk for postoperative instability after arthroplasty.

Dual-Mobility Cup Total Hip Arthroplasty for Displaced Femoral Neck Fractures: A Retrospective Study With a Median Follow-Up of 5 Years

Introduction:

Patient outcomes following modern dual-mobility cup total hip arthroplasty (DM-THA) remains a concern. Few reports have focused on the use of modern DM-THA in the setting of Asian populations for displaced osteoporotic femoral neck fractures (FNFs). This study aimed to investigate the outcomes of Chinese population with displaced osteoporotic FNFs initially treated with modern DM-THA.

Materials and Methods:

Data from 112 consecutive patients (112 hips) with displaced osteoporotic FNFs initially treated with modern DM-THA during 2011-2018 were retrospectively analyzed. Follow-ups were performed at 3 months, 6 months, 12 months, and then every 1 year after surgery. The primary endpoint was the Harris Hip Score (HHS); the secondary endpoint was the main orthopedic complication rate.

Results:

The mean HHS improved from 58.62 (±15.79) prior to surgery to 86.13 (±9.92) at the final follow-up. The main complication rate was 14.2% (16/112). Sixteen complications in 10 patients were recorded. Of the 16 complications, there were 2 (1.7%) cases requiring revision DM-THA, 3 (2.6%) cases of loosening, 2 (1.7%) cases of migration, 3 (2.6%) intra-prosthetic dislocation (IPD), 4 (3.5%) cases of tilting, and 2 (1.7%) cases of severe wear. The need for revision was attributed to prosthesis loosening associated with poor bony quality.

Conclusion:

In patients with displaced osteoporotic FNFs, DM-THA may yield favorable functional outcomes and a low rate of main orthopedic complications, in particular, a low dislocation rate.

Advances and innovations in total hip arthroplasty

Total hip arthroplasty (THA) has been quoted as one of the most successful and cost-effective procedures in Orthopaedics. The last decade has seen an exponential rise in the number of THAs performed globally and a sharp increase in the percentage of young patients hoping to improve their quality of life and return to physically demanding activities. Hence, it is imperative to review the various applications of technology in total hip arthroplasty for improving outcomes. The development of state-of-the-art robotic technology has enabled more reproducible and accurate acetabular positioning, while long-term data are needed to assess its cost-effectiveness. This opinion piece aims to outline and present the advances and innovations in total hip arthroplasty, from virtual reality and three-dimensional printing to patient-specific instrumentation and dual mobility bearings. This illustrates and reflects the debate that will be at the centre of hip surgery for the next decade.

Use of dual mobility components in total hip arthroplasty: Indications and outcomes

Instability after total hip arthroplasty (THA) can be a problematic complication and remains one of the leading causes of revision surgery in the early post-operative period. Dual mobility (DM) implants decrease dislocation risk after THA but they come with their own set of complications. Selective use of DM implants for THA in high risk groups can confer the advantages of this construct while mitigating the risks. In this paper, we review the current literature to examine the evidence for or against use of DM implants in various clinical scenarios and provide an algorithm for when to consider using DM design construct in THA.

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.

Use of dual mobility cups in patients undergoing primary total hip arthroplasty with prior lumbar spine fusion

BACKGROUND

Patients undergoing primary total hip arthroplasty (THA) with prior lumbar spine fusion (LSF) are a high-risk group for instability with reported incidence of dislocation as high as 8.3% using fixed bearing femoral heads. Purpose of this study was to determine risk of post-operative instability in patients undergoing primary THA with a history of prior LSF using dual mobility acetabular cups.

METHODS

This was a multicenter retrospective study with 93 patients undergoing primary THA using a dual mobility cup with a prior history of instrumented LSF. There were 56 females and 47 males with an average age of 66 years (46-87) and average BMI of 30 with mean follow-up of 2.7 years (range 12-124 months). Surgical approach included posterior (63), direct lateral (15), anterior (11), and direct superior (4). Forty-four percent had one level lumbar fusion, 29% with two levels, and 15% with three or more levels fused. The primary outcome investigated was instability.

RESULTS

There were no cases of instability or prosthetic joint infection in this group of patients with prior lumbar spine fusion undergoing primary THA using a dual mobility cup. There was one intra-operative periprosthetic femur fracture and one case of aseptic acetabular cup loosening.

CONCLUSION

Patients undergoing THA with prior LSF are at increased risk for instability due to loss of normal spinopelvic relationship. The use of dual mobility cups in patients with prior LSF undergoing primary THA appears promising with no cases of instability in this high-risk group of patients.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

LEVEL OF EVIDENCE

Level IV, retrospective cohort study.

Dual mobility constructs in revision total hip arthroplasty: survivorship analysis in recurrent dislocation versus other indications at three to twelve-year follow-up

BACKGROUND

The aim of this retrospective study was to evaluate the clinical, radiologic, and survival results of dual mobility (DM) sockets in revision total hip arthroplasty (THA) performed for instability versus revision THAs performed for other reasons.

METHODS

From a computerized database, we identified 84 revision THAs using a modern DM socket performed in 81 patients with a mean age of 71 years. Indication for revision was recurrent dislocation in 47 hips, and other reasons in the remaining 37 hips. A survivorship analysis according to the actuarial method was carried out on the entire series using revision for any cause, revision for dislocation, and radiological cup loosening revised or not, as the end points.

RESULTS

Of the 81 patients, twelve died, six were lost to follow-up, eight had been revised, and 55 patients (58 hips) were unrevised and alive at a mean follow-up of 6.4 years. Dislocation occurred in four of the 47 (8.5%) hips for which indication for revision was dislocation versus one of the remaining 37 (2.7%) hips [odds ratio = 3.4 (0.4-31.3), p = 0.07]. According to our criteria, three acetabular components of which one was revised were considered as loosened. When using revision for dislocation as the end-point, the survival rate at seven years was 90.4 ± 5.3% (IC_95%, 79.9-100) in the 47 hips for which the indication for revision was dislocation versus 100% in the remaining 37 hips (log-rank, p = 0.5).

CONCLUSIONS

The current study indicated that DM sockets represent an interesting solution to prevent dislocation in revision THAs at mid-term follow-up.

Is a hip flip the right trick?

Clinical introductionA 68-year-old man, with known spasticity and a total left hip arthroplasty (THA) performed 6 years ago, was brought to our ED after falling down the stairs. Laying on the stretcher, his left leg was internally rotated and in hyperflexion. An X-ray of the left hip was performed. The diagnosis of posterior hip dislocation was made (figure 1). The patient received sedation and analgesia with 75 mg propofol and 9 mg esketamine intravenously, and a closed reduction procedure was attempted using manual flexion, adduction, traction and internal rotation. Unfortunately, the reduction failed.emermed;37/1/53/F1F1F1Figure 1The patient's X-ray. QUESTION: Why is closed reduction not effective in this case?The femoral head is located more cranially expected, due to material failure. The whole THA should be replaced.This is an anterior dislocation. The closed reduction procedure should be performed by using extension, abduction, traction and internal rotation.The femoral head is not reduced centrally in the acetabulum and the closed reduction procedure should be repeated more forcefully.A dual-mobility cup is used and the liner is not in place anymore. Revision surgery is required. For answer see page 2.

A Retrospective Study to Compare the Efficacy and Postoperative Outcome of Total Hip Arthroplasty with Internal Screw Fixation in Patients with Avascular Necrosis of the Femoral Head

Background

This retrospective study compared the effects of total hip arthroplasty (THA) and traditional surgery using internal screw fixation for the treatment of avascular necrosis (AVN) of the femoral head.

Material/Methods

Two hundred and seventy patients with bilateral AVN of the femoral head were admitted for elective surgery, and 176 patients underwent THA (the THA group), and 94 patients underwent closed reduction screw fixation (the traditional surgery group). The Harris hip score (HHS) was used pre-operatively and to evaluate postoperative outcome.

Results

The mean operation time in the traditional surgery group (82.6±15.6 min) was significantly less compared with the THA group (104.8±14.2 min) (P=0.001). Intraoperative blood loss in the traditional surgery group (219.8±21.6 mL) was significantly less compared with the THA group (339.4±29.4 mL) (P=0.001). After treatment, the mean HHS score of the THA group (76.5±9.2 points) was significantly increased when compared with the traditional surgery group (61.4±10.5 points) (P=0.001). Disease recurrence rate in the THA group was significantly reduced compared with the traditional surgery group (P=0.001). The mean quality of life score of the THA group (85.5±6.4 points) was significantly higher than that of the traditional surgery group (73.4±8.8 points) (P=0.001).

Conclusions

Compared with closed reduction screw fixation, THA for AVN of the femoral head effectively reduced the length of hospital stay, time to recovery, and achieved an improved clinical outcome.

Asymptomatic intraprosthetic dual mobility cup dislocation with increased metal ion levels

With the increased use of dual-mobility cups (DMCs) in total-and revision hip arthroplasties, surgeons can expect an increase of known and new complications. During routine follow-up, we observed an asymptomatic patient with an intraprosthetic-dislocation (IPD) and elevated levels of serum metal ions (1.8 ppb of cobalt and 28.0 ppb of chromium). Revision surgery was inevitable. Perioperative metallosis and severe wear of the metal shell and metal femoral head supported the IPD. Literature showed that the modularity of the DMC can result in increased serum metal ions, create excessive wear, and possibly affect implant survival. Our case and review of the literature may form an argument not to consider DMC for primary cases. Furthermore, we advise yearly clinical and radiological follow-up and, on indication, metal ion testing for DMCs.

Dual mobility acetabular cups for total hip arthroplasty: advantages and drawbacks

INTRODUCTION

The dual mobility cup (DMC) concept was proposed by Professor Gilles Bousquet in 1974. Its' aims were to prevent postoperative dislocation, restore the physiological range of motion of the hip, and reduce the stresses at the interface. Since it was created, this design has been modified multiple times to reduce the complication rate, improve implant survival, and expand the indications.

AREAS COVERED

The objective of this review is to discuss the advantages and disadvantages of this implant based on its 40-year history and also to propose a range of indications based on published results. This will provide surgeons with a complete overview of DMC.

EXPERT COMMENTARY

Published studies on DMC confirm the low dislocation rate. Improvements made to DMC overtime have greatly reduced the complications related to wear, such as aseptic loosening and intraprosthetic dislocation (IPD). According to the literature, the indications have expanded and are no longer limited to revision surgery only. Long-term studies are needed before we can draw formal conclusions and consolidate these promising results.

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.

Cause of irreducible dislocation of a re-revision THR

Instability or recurrent dislocations are a common reason for revision of total hip replacements (THRs). Dual-mobility constructs can help improve stability by increasing the femoral head jump distance. These constructs are used to decrease the risk of re-revision in the setting of recurrent dislocation. This case describes an unusual case of irreducible dislocation of a re-revision THR due to intraprosthetic dislocation. The patient required open reduction and revision of this construct to a tripolar implant. This is important to appreciate from an emergency medicine point of view as repeated attempts at reduction will be fruitless and may result in a femur fracture. This particular type of dislocation is very rare. Perioperative considerations should include early referral to the orthopaedic team for reduction in theatre, and having a low threshold for open reduction. Revision options should be available when bringing a case like this to the operating theatre.

Retrieval evidence of impingement at the third articulation in contemporary dual mobility cups for total hip arthroplasty

PURPOSE

We aimed to assess polyethylene liners of retrieved hips of one design of a dual mobility (DM) cup liner and two designs of femoral stems to better understand the role of femoral stem design on polyethylene impingement.

METHODS

This was a case-control study involving 70 retrieved highly cross-linked polyethylene (X3) liners used with ABGII (n = 35) and Rejuvenate (n = 35) stems (Stryker). All polyethylene liners were assessed for evidence of rim deformation and the damage quantified using metrology methods.

RESULTS

A total of 80% of polyethylene liners paired with ABGII necks had macroscopic evidence of neck impingement resulting in a raised lip whilst 23% of liners paired with Rejuvenate necks had evidence of a raised lip (p < 0.0001). The height of the raised rims of the DM cups paired with ABGII necks had a median (range) of 139 μm (72-255). The height of the raised rims of the DM cups paired with Rejuvenate necks had a median (range) of 52 μm (45-90) (p < 0.0001).

CONCLUSION

Our new findings from retrieved dual mobility bearings showed that polyethylene liner rim deformation resulting from impingement with the femoral neck occurs in early in-human function, is circumferential in distribution, and is affected by the stem neck design. We recommend the use of highly polished and non-edged neck designs when used in conjunction with DM cups.

[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.

Bousquet dual mobility socket for patient under fifty years old. More than twenty year follow-up of one hundred and thirty one hips

PURPOSE

The aim of this study was to analyze dual mobility cup survival rate on young patients under 50 years old at more than 20 years of follow up.

METHODS

One hundred thirty seven hips with a first generation of dual mobility Bousquet cup (Serf) were included. The mean age at the time of the surgery was 41 years and the mean follow-up was 21.9 years.

RESULTS

Twenty year follow-up cup survival rate was 77%. No dislocation occurred, 44 hips were revised (including 21 cup aseptic loosenings isolated, 15 Intra Prosthetic Dislocations), seven hips were lost to follow-up, 11 patients died, and 75 hips were still in situ.

CONCLUSION

First generation dual mobility cup survival on young patient was comparable with literature results. The main complications, cup aseptic loosening and intra prosthetic dislocation, were wear-related. With improvements of the defects of first generation dual mobility, we might expect an even better survival rate with contemporary DM cups.

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.

Low friction arthroplasty and dual mobility cup: a new gold standard

INTRODUCTION

Low friction arthroplasty (LFA) introduced by Sir John Charnley was the gold standard for many years. Dislocation and infection are the first causes for early revision. Late failures are polyethylene (PE) wear and loosening. Due to dislocation risk we slowly switched to the use of LFA with dual mobility cups (DMC). The purposes of this study are (1) to assess whether our changes have improved outcomes and (2) what is the new gold standard?

MATERIAL AND METHODS

We selected from an observational registry of 1,091 cases of hybrid Charnley total hip arthroplasty (THA). The acetabular component was either DMC in 455 cases or fixed cup (FC) in 636 cases.

RESULTS

Three dislocations (0.6%) occurred in the DMC group (none revised). In the FC group 54 dislocated (8.49%) and 20 were recurrent and underwent revision (revision rate 3.14%). In the DMC group, five acetabular and three femoral revisions were performed (revision rate for loosening 1.7%). In the FC group 19 cases underwent acetabular revision, and five cases had femoral component revised (revision rate for loosening 3.7%).

DISCUSSION

Charnley's LFA has proven over 50 years of excellent survivorship. To decrease dislocation risk, one suggested increasing femoral head diameter. Gilles Bousquet proposed another way, namely, the DMC concept. Dislocation is no longer a critical issue with DMC as demonstrated in our series and main series. DMC in primary THA is still a subject of debate. Mid-term results do not demonstrate a higher rate of wear than LFA. What is the current gold standard? LFA was and is our current gold standard in association with a DMC.

Total hip arthroplasty instability in Italy

Hip dislocation is a major and common complication of total hip arthroplasty (THA), which appears with an incidence between 0.3% and 10% in primary total hip arthroplasties and up to 28% in revision THA. The hip dislocations can be classified into three groups: early, intermediate and late. Approximately two-thirds of cases can be treated successfully with a non-operative approach. The rest require further surgical intervention. The prerequisite to developing an appropriate treatment strategy is a thorough evaluation to identify the causes of the dislocation. In addition, many factors that contribute to THA dislocation are related to the surgical technique, mainly including component orientation, femoral head diameter, restoration of femoral offset and leg length, cam impingement and condition of the soft tissues. The diagnosis of a dislocated hip is relatively easy because the clinical situation is very typical. Having identified a dislocated hip, the first step is to perform a closed reduction of the implant. After reduction you must perform a computed tomography scan to evaluate the surgical options for treatment of recurrent dislocation that include: revision arthroplasty, modular components exchange, dual-mobility cups, large femoral heads, constrained cups, elimination of impingement and soft tissue procedures. The objective is to avoid further dislocation, a devastating event which is increasing the number of operations on the hip. To obtain this goal is useful to follow an algorithm of treatment, but the best treatment remains prevention.

Understanding wear in dual mobility total hip replacement: first generation explant wear patterns

PURPOSE

Dual mobility was introduced by Pr. G. Bousquet to improve the dislocation risk of total hip arthroplasty (THR). The wear mechanisms of this implant remain to be understood. Could enhanced explant wear analysis explain liner wear behaviour?

METHODS

Sixty-six explanted liners were selected. Non-destructive 3D scanning and heat colour treatment allowed reporting wear patterns on both convex and concave sides of the liners.

RESULTS

For many liners, liner convexity wear was found to be homogeneous, and linked to a longer implantation time. A few liners had signs of blocking of the convexity, leading to excessive internal damage. Intra prosthetic dislocations were found to only have internal circular wear without liner penetration.

CONCLUSION

Heat colour treatment showed its effectiveness for highlighting wear patterns. Optimal convexity mobility seemed to be leading to a longer implantation time, with decreased contact stresses on concavity. The retentive rim should have a distinct wear analysis.

Five to thirteen year results of a cemented dual mobility socket to treat recurrent dislocation

PURPOSE

Dual mobility (DM) socket has been associated with a low rate of dislocation following both primary and revision total hip arthroplasty (THA). However, little is known about the long-term efficiency of DM in the treatment of THA instability. The purpose of this retrospective study was to evaluate the outcome of a cemented DM socket to treat recurrent dislocation after a minimum of five year follow-up.

METHODS

The series included 51 patients with a mean age of 71.3 ± 11.5 (range, 41-98) years presenting with recurrent dislocation (mean 3.3). A single DM socket design was used consisting of a stainless steel outer shell with grooves with a highly polished inner surface articulating with a mobile polyethylene component. The femoral head was captured in the polyethylene component using a snap-fit type mechanism, the latter acting as a large unconstrained head inside the metal cup.

RESULTS

At the minimum five year follow-up evaluation, 18 of the 51 patients deceased at a mean of 4.8 ± 2.3 years, three were lost to follow-up at a mean of 1.4 years, seven had been revised at a mean of 4.7 ± 3.1 years (range, 1.5-9.1), and the remaining 23 were still alive and did not have revision at a mean of 8.2 ± 2.4 years (range, 5-13 years). Of the seven revision, three were performed for further episodes of dislocation (at the large bearing for one patient and intra-prosthetic for two patients) after a mean 5.9 ± 2.9 years (range, 2.7-9.1), whereas two were performed for late sepsis and two for aseptic loosening of the acetabular component. Radiographic analysis did not reveal any further loosening on the acetabular side. The survival rate of the cup at ten years, using re-dislocation as the end-point, was 86.1 ± 8.4% (95% confidence interval, 69.7-100%). The survival rate of the cup at ten years, using revision for any reason as the end-point, was 75.2 ± 9.3% (95% confidence interval, 56.9-93.5%).

CONCLUSION

A cemented dual mobility cup was able to restore hip stability in 94% of patients presenting with recurrent dislocating hips up to 13-year follow-up with none of the complications associated with constrained devices, as mechanical failure occurred in only 3.9% of the patients of this series. The overall reduced survival using revision for any reason as the end-point at ten years was related to this specific patients population that had various co-morbidities.

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.

Dual-mobility arthroplasty failure: a rationale review of causes and technical considerations for revision

PURPOSE

Dual-mobility arthroplasty is an alternative to conventional total hip arthroplasty (THA) in appropriately selected, active adults with degenerative, necrotic or post-traumatic hip disease or with revision hip arthroplasty. Numerous papers have been published with results of dual-mobility arthroplasty, but there have been no comprehensive literature reviews that summarise the most recent findings and help the orthopaedic surgeon facing different scenarios in which revision of one or both components of a dual-mobility arthroplasty is indicated.

METHODS

We performed a PubMed search for papers published on dual-mobility arthroplasty that provided data on revision and add our experience in order to describe different revision scenarios. We collected data on revision for any reason, for aseptic loosening, for infection, or for dislocation. For each complication, we summarise causes and diagnosis of this complication and describe the direction of possible therapeutic options.

RESULTS

The dual-mobility arthroplasty offers the benefit of increased stability without compromising clinical outcomes and implant longevity. However, as with conventional arthroplasties, complications are also reported, with the most frequent being cup loosening, dislocation, accelerated wear and infection. Dual-mobility implants also have some specific complications secondary to their specific design, with the presence of a third joint. For example, intraprosthetic dislocation due to retentive failure of the polyethylene (PE) liner on the femoral head is a complication observed exclusively with this type of implant and involves articulation failure between the femoral head and the PE liner. Mechanical conflict with the iliopsoas tendon has also been reported, probably due to femoral head size, cup design, and/or a dysplastic hip. This systematic review of the literature identified several options for treating each complication, and in particular, options regarding conserving or not of one the two articulating devices.

CONCLUSIONS

These findings can inform discussions relating to risks and benefits of different therapeutic options when performing revision of a dual-mobility arthroplasty.