Dual mobility cups have two points of articulation, one between the shell and the polyethylene (external bearing) and one between the polyethylene and the femoral head (internal bearing). Movement occurs at the inner bearing; the outer bearing only moves at extremes of movement. Dislocation after total hip arthroplasty (THA) is a cause of much morbidity and its treatment has significant cost implications. Dual mobility cups provide an increased range of movement and a may reduce the risk of dislocation. . This paper reviews the use of these cups in THA, particularly where stability is an issue. Dual mobility cups may be of benefit in primary THA in patients at a high risk of dislocation, such as those who are older with increased comorbidities and a higher American Association of Anesthesiology grade and those with a neuromuscular disease. They may be used at revision surgery where the risk of dislocation is high, such as in patients with many prior dislocations, or those with abductor deficiency. They may also be used in THA for displaced fractures of the femoral neck, which has a notoriously high rate of dislocation. Cite this article: Bone Joint J 2016;98-B(1 Suppl A):60–3

Background. Published simulator studies for metal/UHMWPE bearings couples showed that increasing the femoral head diameter by 1 mm increases wear by approximately 10% due to increased contact area. Therefore, there are concerns about increased wear with dual mobility hip bearings. Purpose of the study. The purpose of the study was to compare wear from dual mobility hip bearings to that with traditional fixed bearings. In addition, for the dual mobility bearings, the effect of femoral head material type on the liner wear was also evaluated. Methods. The bearings selected for the study are listed in Table 1. Prior to the start of the test all liners were soaked in lubricant for 48 hours. Hip testing was performed on a Shore Western Orbital Bearing machine in the anatomically oriented position. A simulated gait profile (synchronized at +/-23° biaxial rocking motion) with a minimum/maximum 200/2000N force was applied to the bearings at frequency of 1Hz. The lubricant used for the testing was 25% bovine serum with 0.2 % sodium azide, 20 mMol EDTA and distilled water. The test was interrupted at regular intervals for gravimetric assessment of wear amount. Findings of Study. Figure 1 shows total wear at 3 Mc and wear rates (determined from the slope of the linear regression) for all the groups. At 3 Mc, dual mobility bearings with stainless steel femoral head demonstrated 5% lower wear rate than those articulated against CoCrMo femoral heads. However, there was no statistically significant difference in the observed wear rate due to the femoral head material type. The results from the study also exhibited lower wear and wear rate for dual mobility bearings compared to fixed bearings. Dual mobility bearings with CoCrMo femoral head and stainless steel femoral head demonstrated 17% and 21% lower wear rate when compared to fixed bearings. Although dual mobility bearings possess greater contact area (due to the contact between head-liner and liner-shell compared to only head-liner in fixed bearings), no such increased trend in wear was observed. Conclusions. Dual mobility hip bearings are designed to reduce the risk of dislocation and allow for increased range of motion thus improving joint function and stability. The results from the study demonstrate that dual mobility bearings have comparable wear properties when compared to fixed bearings. For figure/table, please contact authors directly

Aims. Instability remains a challenging problem in both primary and revision total hip arthroplasty (THA). Dual mobility components confer increased stability, but there are concerns about the unique complications associated with these designs, as well as the long-term survivorship. Materials and Methods. We performed a systematic review of all English language articles dealing with dual mobility THAs published between 2007 and 2016 in the MEDLINE and Embase electronic databases. A total of 54 articles met inclusion criteria for the final analysis of primary and revision dual mobility THAs and dual mobility THAs used in the treatment of fractures of the femoral neck. We analysed the survivorship and rates of aseptic loosening and of intraprosthetic and extra-articular dislocation. Results. For the 10 783 primary dual mobility THAs, the incidence of aseptic loosening was 1.3% (142 hips); the rate of intraprosthetic dislocation was 1.1% (122 hips) and the incidence of extra-articular dislocation was 0.46% (41 hips). The overall survivorship of the acetabular component and the dual mobility components was 98.0%, with all-cause revision as the endpoint at a mean follow-up of 8.5 years (2 to 16.5). For the 3008 revision dual mobility THAs, the rate of aseptic acetabular loosening was 1.4% (29 hips); the rate of intraprosthetic dislocation was 0.3% (eight hips) and the rate of extra-articular dislocation was 2.2% (67 hips). The survivorship of the acatabular and dual mobility components was 96.6% at a mean of 5.4 years (2 to 8). For the 554 dual mobility THAs which were undertaken in patients with a fracture of the femoral neck, the rate of intraprosthetic dislocation was 0.18% (one hip), the rate of extra-articular dislocation was 2.3% (13 hips) and there was one aseptic loosening. The survivorship was 97.8% at a mean of 1.3 years (0.75 to 2). Conclusion. Dual mobility articulations are a viable alternative to traditional bearing surfaces, with low rates of instability and good overall survivorship in primary and revision THAs, and in those undertaken in patients with a fracture of the femoral neck. The incidence of intraprosthetic dislocation is low and limited mainly to earlier designs. High-quality, prospective, comparative studies are needed to evaluate further the use of dual mobility components in THA. Cite this article: Bone Joint J 2018;100-B:11–19

Aims. Prior studies have identified that malseating of a modular dual mobility liner can occur, with previous reported incidences between 5.8% and 16.4%. The aim of this study was to determine the incidence of malseating in dual mobility implants at our institution, assess for risk factors for liner malseating, and investigate whether liner malseating has any impact on clinical outcomes after surgery. Methods. We retrospectively reviewed the radiographs of 239 primary and revision total hip arthroplasties with a modular dual mobility liner. Two independent reviewers assessed radiographs for each patient twice for evidence of malseating, with a third observer acting as a tiebreaker. Univariate analysis was conducted to determine risk factors for malseating with Youden’s index used to identify cut-off points. Cohen’s kappa test was used to measure interobserver and intraobserver reliability. Results. In all, 12 liners (5.0%), including eight Stryker (6.8%) and four Zimmer Biomet (3.3%), had radiological evidence of malseating. Interobserver reliability was found to be 0.453 (95% confidence interval (CI) 0.26 to 0.64), suggesting weak inter-rater agreement, with strong agreement being greater than 0.8. We found component size of 50 mm or less to be associated with liner malseating on univariate analysis (p = 0.031). Patients with malseated liners appeared to have no associated clinical consequences, and none required revision surgery at a mean of 14 months (1.4 to 99.2) postoperatively. Conclusion. The incidence of liner malseating was 5.0%, which is similar to other reports. Component size of 50 mm or smaller was identified as a risk factor for malseating. Surgeons should be aware that malseating can occur and implant design changes or changes in instrumentation should be considered to lower the risk of malseating. Although further follow-up is needed, it remains to be seen if malseating is associated with any clinical consequences. Cite this article: Bone Jt Open 2021;2(10):858–864

Dislocation and instability remain leading cause of failure following THA. We present a single-surgeon 10-year experience with use of Dual Mobility (DM) bearings in Primary and Revision THA using posterior approach. 127 DM bearings were implanted between September 2006 – September 2016; 102 in high-risk primary THA's and 25 revision THA's for either treatment or prevention of instability. Selection for DM bearing followed individual patient risk assessment. Criteria for use of DM bearing were presence of multiple risk factors. Mean age was 72.9 years. 100 Mono-block DM implants, 22 Modular DM implants and 5 custom-made DM devices were implanted. Revision cohort included those used in conjunction with a cage or porous metal augments. 2 dislocations (1.6%) were observed, both in the Revision group, 1 was recurrent requiring revision to constrained liner. Primary group had 2 revisions; 1 peri-prosthetic fracture and 1 deep infection. No DM bearing specific complications were observed. A constructed life table calculated survival function with endpoint set as revision for any reason demonstrated a cumulative survival of 94% at 7.4 years. In high-risk patients, DM bearings are successful at preventing and treating dislocation in THA. Primary cohort in this study all had multiple risk factors for instability but no dislocations or bearing specific complications were observed. Dislocations observed in Revision group were associated with major soft tissue deficiency. This study adds to the promising results already reported with DM THA articulations and should be considered for patients at risk of dislocation or instability. Runner Up – Best Paper Award

Dislocation is still one of the more common reasons for revision of THR.Registry and large institutional data has demonstrated the effectiveness of Dual Mobility articulations in reducing revision for dislocation after THR. There is little data about whether the use of dual mobility is associated with a comprised clinical functional outcome. This study aimed to ascertain whether the use of Dual Mobility articulations (DM cups) comes within a compromise to the functional of the THR procedure as measured by the Hip disability and Osteoarthritis Outcome Score (HOOS). Utilising a retrospective design, patients were grouped into those with DM cups with 12 PROMs (Cohort 1) or a large data base of all THR procedures also with a complete set of 12 month PROMs (Cohort 2). The 2 groups were matched for age and gender through propensity score matching. The comparison focused on five domains of the HOOS: Pain, Symptoms, Activities of Daily Living (ADL), Sports and Recreation, and Quality of Life (QOL) at 6- and 12-months post-operation. 12 month PROM data suggested a convergence in scores for several domains, no uniform superiority of one articulation type over the other was found across all domains. These results suggest that both DM cup and standard articulations can effectively improve patient-reported outcomes in THR surgeries, but there are variations in recovery within each cohort that are potentially influenced by factors beyond the articulation type. This study contributes to the ongoing dialogue on optimising prosthetic selection to enhance recovery trajectories and quality of life for THR patients, emphasising the critical role of evidence-based decision-making in orthopaedic surgery

Background. Dual mobility bearings are an attractive treatment option to obtain hip stability during challenging primary and revision total hip arthroplasty (THA) cases. Despite growing enthusiasm in the United States, long-term results of modern dual mobility implants are lacking. The purpose of this study is to analyze data submitted to the American Joint Replacement Registry (AJRR) to characterize utilization trends of dual mobility bearings in the United States. Methods. All primary and revision THA procedures reported to AJRR from 2012–2018 were analyzed. Patients of all ages were included and subdivided into dual mobility and traditional bearing surface cohorts. Independent variables included patient demographics, geographic region, hospital size, and teaching affiliation. Associations were determined by chi-square analysis and a logistic regression was performed to assess the association between dual mobility and independent 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 dual mobility implants respectively. For primary THA, dual mobility utilization increased from 6.7% in 2012 to 12.0% in 2018. (Figure 1) Similarly, amongst revision THA, dual mobility utilization increased from 19.5% in 2012 to 30.6% in 2018. Patients <50 years of age had the highest rates of dual mobility utilization in every year examined. (Figure 2) For every year increase in age, there was a 0.4% decrease in the rate of dual mobility utilization (odds ratio [OR] 0.996, 95% confidence interval [CI] 0.995–0.997, p<0.001). (Table 1) Females were more likely to receive a dual mobility implant compared to males (OR 1.077, 95% CI 1.054–1.100, p<0.001). Major teaching institutions and smaller hospitals were associated with higher rates of utilization. The West was associated with the highest rate of dual mobility usage compared to the other regions of the United States. Dual mobility articulations were used most commonly for dysplasia (OR 2.448 vs osteoarthritis, 95% CI 1.143–1.285, p<0.001) during primary THA and for instability (OR 3.130 vs poly-wear, 95% CI 2.751–3.562, p<0.001) in the revision setting. (Table 2). Conclusion. Dual mobility 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 geographic location were associated with increased utilization. For any tables or figures, please contact the authors directly

Aims. Dual mobility implants in total hip arthroplasty are designed to increase the functional head size, thus decreasing the potential for dislocation. Modular dual mobility (MDM) implants incorporate a metal liner (e.g. cobalt-chromium alloy) in a metal shell (e.g. titanium alloy), raising concern for mechanically assisted crevice corrosion at the modular liner-shell connection. We sought to examine fretting and corrosion on MDM liners, to analyze the corrosion products, and to examine histologically the periprosthetic tissues. Methods. A total of 60 retrieved liners were subjectively scored for fretting and corrosion. The corrosion products from the three most severely corroded implants were removed from the implant surface, imaged using scanning electron microscopy, and analyzed using Fourier-transform infrared spectroscopy. Results. Fretting was present on 88% (53/60) of the retrieved liners, and corrosion was present on 97% (58/60). Fretting was most often found on the lip of the taper at the transition between the lip and the dome regions. Macrophages and particles reflecting an innate inflammatory reaction to corrosion debris were noted in six of the 48 cases for which periprosthetic tissues were examined, and all were associated with retrieved components that had high corrosion scores. Conclusion. Our results show that corrosion occurs at the interface between MDM liners and shells and that it can be associated with reactions in the local tissues, suggesting continued concern that this problem may become clinically important with longer-term use of these implants. Cite this article: Bone Joint J 2021;103-B(7):1238–1246

In metal-on-metal (MoM) hip replacements or resurfacings, mechanical induced corrosion can lead to a local inflammatory response, pseudo tumours and elevated serum metal ions, requiring revision surgery. The size and diametral clearance of Anatomic (ADM) and Modular (MDM) Dual Mobility bearings matches that of certain MOM components. Presenting the opportunity for revision with exchange of the metal head for ADM/MDM bearings without removal of the acetabular component if it is well-fixed and appropriately positioned. Between 2012 and 2020, across two centres, 94 patients underwent revision of a MoM hip replacement or resurfacing. The mean age was 65.5 (33–87) years. In 53 patients (56.4%), the acetabular component was retained, and dual mobility bearings were used (DM); in 41 (43.6%) the acetabulum was revised (AR). DM was only considered where the acetabular component was satisfactorily positioned and well-integrated into bone, with no surface damage. Patients underwent clinical and radiographic follow-up to at least one-year (mean 42.4 (12–96) months). One (1.1%) patient died before one-year, for reasons unrelated to the surgery. In the DM group, two (3.8%) patients underwent further surgery; one (1.9%) for dislocation and one (1.9%) for infection. In the AR group, four (12.2%) underwent further procedures; two (4.9%) for loosening of the acetabular component and two (4.9%) following dislocations. There were no other dislocations in either group. In the DM group, operative time (68.4 v 101.5 mins, p<0.001), postoperative drop in haemoglobin (16.6 v 27.8 g/L, p<0.001), and length of stay (1.8 v 2.4 days, p<0.001) were significantly lower. There was a significant reduction in serum metal ions postoperatively in both groups (p<0.001 both Cobalt and Chromium) although there was no difference between groups for this reduction (p=0.674 Cobalt; p=0.186 Chromium). In selected patients with MoM hip arthroplasty, where the acetabular component is well-fixed, in a satisfactory position and there is no surface damage, the metal head can be exchanged for ADM/MDM bearings with retention of the acetabular prosthesis. Presenting significant benefits through a less invasive procedure, and a low risk of complications, including dislocation

Dislocation remains among the most common complications of, and reasons for, revision of both primary and revision total hip arthroplasties in the United States. We have advocated identifying the primary cause of instability to plan appropriate treatment (Wera, Della Valle, et al., JOA 2012). Once implant position, leg length, and offset have been optimised and sources of impingement have been removed, the surgeon can opt for a large femoral head, a dual mobility articulation or a constrained liner. Given the limitations of constrained liners, we have looked to dual mobility articulations as an alternative, including its use in patients with abductor deficiency. We retrospectively compared a consecutive series of revision THA that were at high risk for instability and treated with either a constrained liner or a dual mobility articulation. At a minimum of two years, there were ten dislocations in the constrained group (10/43 or 23.3%) compared to three in the dual-mobility group (3/36 or 8.3%; p = 0.06). With repeat revision for instability as an endpoint, the failure rate was 23% for the constrained group and 5.5% for the dual mobility group (p = 0.03). We have also performed a systematic review of the published literature on the use of dual mobility in revision THA. Of the 3,088 hips reviewed, the dislocation rate was 2.2%, the risk of intraprosthetic dislocation was 0.3% and overall survivorship was 96.6% at 5 years. Dual mobility articulations offer anatomic sized femoral heads that greatly increase jump distance, without many of the negatives of a constrained liner. While dual mobility is associated with its own concerns and problems (including intraprosthetic dislocation and wear) our initial results suggest that they are a viable alternative to a constrained liner, even in the most challenging situations

Introduction. Enhanced stability using dual mobility has been demonstrated but concerns about potential for corrosion in modular versions have been raised. Case reports of corrosion with malseated inserts have heightened concerns over this modularity. Some have claimed that malseating is rare, the true frequency is unknown. The purpose of our investigation was to determine the incidence of liner malseating in dual mobility implants at our institution. Methods. 567 hips had primary modular dual mobility hip replacements (Biomet or Stryker) between 2016 and 2018. Post-operative radiographs were reviewed independently by two reviewers to identify malseating. Liners were considered malseated if there was a noticeable gap between the metal liner and acetabular shell(figure 1). All liners deemed to be malseated were independently assessed by 3 separate reviewers for confirmation. Results. 32 of the 567 (5.6%) of the liners were found to be malseated. There were no malseated liners in the Biomet group (n=46). There were 32 malseated liners in 521 (6.1%) Stryker cups using 3 different Stryker shells: 19 of 229 (8.23%) in the Trident I hemispherical group; 5 of 99 (5.05%) in in the Trident I PSL group and 8 of 193 (4.15%) in the Trident II group. Conclusions. Our observation of malseating in 5.6% of patients is clearly disconcerting. The etiology of malseating is unclear ranging from soft tissue interposition to possible shell deformation leading to a geometric mismatch between cup and liner. The clinical impact of this observation is unknown but speculation regarding risk of micromotion along the interface leading to fretting and corrosion appears plausible. Further clinical followup will be necessary to determine whether these radiographic finding will ultimately impact clinical outcome. For any tables or figures, please contact the authors directly

Dual mobility components for total hip arthroplasty provide for an additional articular surface, with the goals of improving range of motion, jump distance, and overall stability of the prosthetic hip joint. A large polyethylene head articulates with a polished metal acetabular component, and an additional smaller metal head is snap-fit into the large polyethylene. New components have been released for use in North America over the past four years. In some European centers, these components are routinely used for primary total hip arthroplasty. Some surgeons in USA suggest routine use in primary hip arthroplasty. However, their greatest utility is to manage recurrent dislocation in the setting of revision total hip arthroplasty. Recent biomechanical data suggests that, in a 3D CT scan-cadaver hip model, there is no difference in range of motion between a 36mm head and an ADM dual mobility component sizes 50–56mm. There is little wear data on dual mobility components, except from one implant manufacturer. It is feared that there is a “3rd articulation” in dual mobility components—the routine impingement of the femoral neck against the polyethylene femoral head. Several retrospective series have shown satisfactory results for these dual mobility components at short- to medium-term follow-up times. There are important concerns with polyethylene wear, late intra-prosthetic dislocation, and the lack of long-term follow-up data. Big femoral heads (36mm and 40mm) articulating with highly cross-linked, e-beam, remelted, polyethylene are a better choice in primary total hip arthroplasty, to decrease the frequency of dislocation in “high risk” patients. Although the risk of early dislocation was 4% in “high risk” patients, there was no recurrence, no revision, and no late first dislocation. Until further long-term results are available, caution is advised in the routine use of dual mobility components in primary total hip arthroplasty

Introduction. Patients undergoing primary total hip arthroplasty (THA) with prior lumbar spine fusion (LSF) are at high risk for instability with reported incidence of dislocation as high as 8.3%. The use of dual mobility cups in patients undergoing revision THA, another high risk group, has demonstrated decreased incidence of instability. Purpose of this study was to evaluate the risk of instability in patients undergoing primary THA with a history of prior LSF using dual mobility cups. Methods. This was a multi-center retrospective study with 93 patients undergoing primary THA using a dual mobility cup with prior history of instrumented LSF. The primary outcome investigated was instability. Secondary variables investigated included number of levels fused, approach, length of stay, and other complications. The minimum follow-up time was 1 year since the majority of dislocations occur during first year following the primary THA. Results. There were 56 females and 47 males with average age of 66 years (46–87) and average BMI of 30. Mean follow up was 31 months (range 12 – 124.2). Surgical approach included: posterior (63), direct lateral (15), anterior (11), direct superior (4). 44% had one level fusion, 29% with 2 levels, and 15% with 3 or more levels fused. There were no dislocations or infections in this study group. There was one intraoperative fracture and one DVT. Conclusions. Patients undergoing primary THA with prior LSF are a high risk group with an increased risk for instability due to the loss of normal spino-pelvic relationship. The use of dual mobility cups in a high risk group of patients in this study demonstrated excellent results with no incidence of dislocation. Despite the limitations in this study with varying approaches and multiple sites, the use of dual mobility cups to decrease the incidence of instability in patients with prior LSF appears promising. For any tables or figures, please contact the authors directly

Dual mobility components for total hip arthroplasty provide for an additional articular surface, with the goals of improving range of motion, jump distance, and overall stability of the prosthetic hip joint. A large polyethylene head articulates with a polished metal acetabular component, and an additional smaller metal head is snap-fit into the large polyethylene. The first such device was introduced for primary total hip arthroplasty by Bousquet in the 1970s, thus, the “French connection”. Dual mobility components have been released for use in North America over the past five years. In some European centers, these components are routinely used for primary total hip arthroplasty. However, their greatest utility may be to manage recurrent dislocation in the setting of revision total hip arthroplasty. Several retrospective series and the Swedish hip registry have shown satisfactory results for this indication at short- to medium-term follow-up times. However, there are important concerns with polyethylene wear, late intraprosthetic dislocation, and the lack of long-term follow-up data. These components are an important option in the treatment of recurrent dislocation in younger patients, revision of failed metal-metal resurfacing, and salvage of failed constrained liners. There are more recent concerns of possible iliopsoas tendinitis, elevated metal levels with one design, and acute early intraprosthetic dislocation following attempted closed reduction. However, a dual mobility component may now be the preferred solution in revision surgery for recurrent hip dislocation

Treatment of recurrent dislocation: approximately: 1/3 of failures (probably higher in the absence of a clear curable cause). In the US: most popular treatment option: constrained liners with high redislocation and loosening rates in most reports. Several interfaces leading to various modes of failures. In Europe: dual mobility cups (or tripolar unconstrained): first design Gilles Bousquet 1976 (Saint Etienne, France), consisting of a metal shell with a highly polished inner surface articulating with a mobile polyethylene insert (large articulation). The femoral head is captured into the polyethylene (small articulation) using a snap fit type mechanism leading to a large effective unconstrained head inside the metal cup. With dual mobility, most of the movements occur in the small articulation therefore limiting wear from the large polyethylene on metal articulation. Contemporary designs include: CoCr metal cup for improved friction, outer shell coated with titanium and hydroxyapatite, possible use of screws to enhance primary stability (revision), cemented version in case of major bone defect requiring bone reconstruction. Increased stability obtained through an ultra-large diameter effective femoral head increasing the jumping distance. Dual mobility in revision for recurrent dislocation provided hip stability in more than 94% of the cases with less than 3% presenting redislocation up to 13-year follow-up. A series from the UK concerning 115 revisions including 29 revisions for recurrent dislocation reported 2% dislocation in the global series and 7% re-dislocation in patients revised for instability. A recent report of the Swedish hip arthroplasty register including 228 patients revised for recurrent dislocation showed 99% survival with revision for dislocation as the endpoint and 93% with revision for any reason as the endpoint. One specific complication of dual mobility sockets: intra-prosthetic dislocation (ie: dislocation at the small articulation): often asymptomatic or slight discomfort, eccentration of the neck on AP radiograph, related to wear and fatigue of the polyethylene rim at the capturing are through aggressive stem neck to mobile polyethylene insert contact (3rd articulation). Risk factors include: large and aggressive femoral neck design implants, small head/neck ratio, skirted heads, major fibrosis and periprosthetic ossifications. Current (over ?) use in France: 30% of primary THA, 60% in revision THA. Proposed (reasonable) indications: primary THA at high risk for dislocation, revision THA for instability and/or in case of abductors deficiency, Undisputed indication: recurrent dislocation

Dual mobility components for total hip arthroplasty provide for an additional articular surface, with the goals of improving range of motion, jump distance, and overall stability of the prosthetic hip joint. A large polyethylene head articulates with a polished metal acetabular component, and an additional smaller metal or ceramic head is snap-fit into the large polyethylene. In some European centers, these components are routinely used for primary total hip arthroplasty. However, their greatest utility will be to prevent and manage recurrent dislocation in the setting of revision total hip arthroplasty. Several retrospective series have shown satisfactory results for this indication at medium-term follow-up times. The author has used dual mobility components on two occasions to salvage a failed constrained liner. At least one center reports that dual mobility outperforms 40mm femoral heads in revision arthroplasty. Modular dual mobility components, with screw fixation, are the author's first choice for the treatment of recurrent dislocation, revision of failed metal-metal resurfacing, total hips, unipolar arthroplasties, and salvage of failed constrained liners. There are concerns of elevated metal levels with one design, and acute early intra-prosthetic dissociation following attempted closed reduction. Total hip surgeons no longer cement Charnley acetabular components, use conventional polyethylene, autologous blood donation, or a drain; now constrained components join these obsolete techniques! In 2017, a dual mobility component, rather than a constrained liner, is the preferred solution in revision surgery to prevent and manage recurrent dislocation

Introduction. Dual-mobility bearings increase the stable range of motion of total hip arthroplasty (THA) but are limited by the mechanical effects of a large diameter metal on polyethylene bearing which may cause high rates of wear from the surfaces of the polyethylene bearing and the head-stem taper. Improved polyethylene (PE) has reduced concern over bearing wear but the effects on the taper junction are unknown. We aimed to better understand the effect of dual mobility bearings on fretting-corrosion damage to the taper junction by comparison to standard bearings. Materials and Methods. We collected and analysed retrieved hips of one design with either dual mobility (n= 39) or standard bearings (n=30). The bearing size in the dual mobility group was 42mm whereas in the standard bearing group it had a median of 36mm. Stem trunnions had V40 tapers. Time of implantation and body mass index were comparable between the two groups. Fretting and corrosion at the stem trunnions was quantified by: 1) visual scoring and 2) surface profilometry. Results. Corrosion and fretting of the head-stem taper junction was lower in the dual mobility group when compared to the standard group as measured by both visual scoring (p=0.0002) and surface profilometry to measure material loss (p<0.0001). We did not see black debris, characteristic of severe corrosion processes, at the male surfaces in the dual mobility group. Discussion. In this study, visual damage at the male taper surfaces of dual mobility systems was less that that occurring at the male taper surfaces of standard articulating systems, measurements of wear rates were in agreements with the macroscopic evaluation. Conclusions. The frictional torque on the head-stem taper junction may be reduced with the use of a dual-mobility system when compared to a standard bearing system

Dual mobility components for total hip arthroplasty provide for an additional articular surface, with the goals of improving range of motion, jump distance, and overall stability of the prosthetic hip joint. A large polyethylene head articulates with a polished metal acetabular component, and an additional smaller metal or ceramic head is snap-fit into the large polyethylene. In some European centers, these components are routinely used for primary total hip arthroplasty. However, their greatest utility will be to prevent and manage recurrent dislocation in the setting of revision total hip arthroplasty. Several retrospective series have shown satisfactory results for this indication at medium-term follow-up times. The author has used dual mobility components on two occasions to salvage a failed constrained liner. At least one center reports that dual mobility outperforms 40mm femoral heads in revision arthroplasty. Modular dual mobility components, with screw fixation, are the author's first choice for the treatment of recurrent dislocation, revision of failed metal-on-metal resurfacing or total hips, unipolar arthroplasties, and salvage of failed constrained liners. There are concerns of elevated metal levels with one design, and acute early intra-prosthetic dissociation following attempted closed reduction. Total hip surgeons no longer use conventional polyethylene, autologous blood donation, or a hemovac drain; now constrained components join these obsolete techniques! In 2018, a dual mobility component, rather than a constrained liner, is the preferred solution in revision surgery to prevent and manage recurrent dislocation

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

Dual mobility components for total hip arthroplasty provide for an additional articular surface, with the goals of improving range of motion, jump distance, and overall stability of the prosthetic hip joint. A large polyethylene head articulates with a polished metal acetabular component, and an additional smaller metal or ceramic head is snap-fit into the large polyethylene. New components have been released for use in North America over the past eight years and additional modular designs will be forthcoming. In some European centers, these components are routinely used for primary total hip arthroplasty. However, their greatest utility may be to prevent and manage recurrent dislocation in the setting of revision total hip arthroplasty. Several retrospective series have shown satisfactory results for this indication at medium-term follow-up times. The author has used dual mobility components on two occasions to salvage a failed constrained liner. However, at least one center reported failure of dual mobility if the abductor mechanism is absent. There are important concerns with dual mobility, including late polyethylene wear causing intra-prosthetic dislocation, and the lack of long-term follow-up data with most designs. Modular dual mobility components, with screw fixation, are the author's first choice for the treatment of recurrent dislocation in younger patients, revision of failed metal-metal resurfacing, total hips, large head unipolar arthroplasties, and salvage of failed constrained liners. There are more recent concerns of iliopsoas tendonitis, elevated metal levels with one design, and acute early intra-prosthetic dissociation following attempted closed reduction. However, in 2016, a dual mobility component, rather than a constrained liner, may be the preferred solution in revision surgery to prevent and manage recurrent dislocation