Aims. Dislocation is the most common indication for further surgery following total hip arthroplasty (THA) when undertaken in patients with a femoral neck fracture. This study aimed to assess the complication rates of THA with dual mobility components (THA-DMC) following a femoral neck fracture and to compare outcomes between THA-DMC, conventional THA, and hemiarthroplasty (HA). Methods. We performed a systematic review of all English language articles on THA-DMC published between 2010 and 2019 in the MEDLINE, EMBASE, and Cochrane databases. After the application of rigorous inclusion and exclusion criteria, 23 studies dealing with patients who underwent treatment for a femoral neck fracture using THA-DMC were analyzed for the rate of dislocation. Secondary outcomes included reoperation, periprosthetic fracture, infection, mortality, and functional outcome. The review included 7,189 patients with a mean age of 77.8 years (66.4 to 87.6) and a mean follow-up of 30.9 months (9.0 to 68.0). Results. THA-DMC was associated with a significantly lower dislocation rate compared with both THA (OR 0.26; 95% CI 0.08 to 0.79) and HA (odds ratio (OR) 0.27; 95% confidence interval (CI) 0.15 to 0.50). The rate of large articulations and of intraprosthetic dislocation was 1.5% (n = 105) and 0.04% (n = 3) respectively. Conclusion. THA-DMC when used in patients with a femoral neck fracture is associated with a lower dislocation rate compared with conventional arthroplasty options. There was no increase in the rates of other complication when THA-DMC was used. Future cost analysis and prospective, comparative studies are required to assess the potential benefit of using THA-DMC in these patients. Cite this article: Bone Joint J 2020;102-B(7):811–821

Objectives. The annual incidence of hip fracture is 620 000 in the European Union. The cost of this clinical problem has been estimated at 1.75 million disability-adjusted life years lost, equating to 1.4% of the total healthcare burden in established market economies. Recent guidance from The National Institute for Health and Clinical Excellence (NICE) states that research into the clinical and cost effectiveness of total hip arthroplasty (THA) as a treatment for hip fracture is a priority. We asked the question: can a trial investigating THA for hip fracture currently be delivered in the NHS?. Methods. We performed a contemporaneous process evaluation that provides a context for the interpretation of the findings of WHiTE Two – a randomised study of THA for hip fracture. We developed a mixed methods approach to situate the trial centre within the context of wider United Kingdom clinical practice. We focused on fidelity, implementation, acceptability and feasibility of both the trial processes and interventions to stakeholder groups, such as healthcare providers and patients. Results. We have shown that patients are willing to participate in this type of research and that surgeons value being part of a team that has a strong research ethos. However, surgical practice does not currently reflect NICE guidance. Current models of service delivery for hip fractures are unlikely to be able to provide timely total hip arthroplasty for suitable patients. Conclusions. Further observational research should be conducted to define the population of interest before future interventional studies are performed. Cite this article: C. Huxley, J. Achten, M. L. Costa, F. Griffiths, X. L. Griffin. A process evaluation of the WHiTE Two trial comparing total hip arthroplasty with and without dual mobility component in the treatment of displaced intracapsular fractures of the proximal femur: Can a trial investigating total hip arthroplasty for hip fracture be delivered in the NHS? Bone Joint Res 2016;5:444–452. DOI: 10.1302/2046-3758.510.BJR-2015-0008.R1

Aims

Modular dual mobility (MDM) acetabular components are often used with the aim of reducing the risk of dislocation in revision total hip arthroplasty (THA). There is, however, little information in the literature about its use in this context. The aim of this study, therefore, was to evaluate the outcomes in a cohort of patients in whom MDM components were used at revision THA, with a mean follow-up of more than five years.

Aims

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

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

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

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

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

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

Aims. One-stage revision hip arthroplasty for periprosthetic joint infection (PJI) has several advantages; however, resection of the proximal femur might be necessary to achieve higher success rates. We investigated the risk factors for resection and re-revisions, and assessed complications and subsequent re-revisions. Methods. In this single-centre, case-control study, 57 patients who underwent one-stage revision arthroplasty for PJI of the hip and required resection of the proximal femur between 2009 and 2018 were identified. The control group consisted of 57 patients undergoing one-stage revision without bony resection. Logistic regression analysis was performed to identify any correlation with resection and the risk factors for re-revisions. Rates of all-causes re-revision, reinfection, and instability were compared between groups. Results. Patients who required resection of the proximal femur were found to have a higher all-cause re-revision rate (29.8% vs 10.5%; p = 0.018), largely due to reinfection (15.8% vs 0%; p = 0.003), and dislocation (8.8% vs 10.5%; p = 0.762), and showed higher rate of in-hospital wound haematoma requiring aspiration or evacuation (p = 0.013), and wound revision (p = 0.008). The use of of dual mobility components/constrained liner in the resection group was higher than that of controls (94.7% vs 36.8%; p < 0.001). The presence and removal of additional metal hardware (odds ratio (OR) = 7.2), a sinus tract (OR 4), ten years’ time interval between primary implantation and index infection (OR 3.3), and previous hip revision (OR 1.4) increased the risk of proximal femoral resection. A sinus tract (OR 9.2) and postoperative dislocation (OR 281.4) were associated with increased risk of subsequent re-revisions. Conclusion. Proximal femoral resection during one-stage revision hip arthroplasty for PJI may be required to reduce the risk of of recurrent or further infection. Patients with additional metalware needing removal or transcortical sinus tracts and chronic osteomyelitis are particularly at higher risk of needing proximal femoral excision. However, radical resection is associated with higher surgical complications and increased re-revision rates. The use of constrained acetabular liners and dual mobility components maintained an acceptable dislocation rate. These results, including identified risk factors, may aid in preoperative planning, patient consultation and consent, and intraoperative decision-making. Cite this article: Bone Joint J 2021;103-B(11):1678–1685

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

Background:. Dual mobility components in total hip arthroplasty have been successfully in use in Europe for greater than 25 years. However, these implants have only recently obtained FDA approval and acceptance among North American arthroplasty surgeons. Both decreased dislocation rate and decreased wear rates have been proposed benefits of dual mobility components. These components have been used for primary total hip arthroplasty in patients at high risk for dislocation, total hip arthroplasty in the setting of femoral neck fracture, revision for hip instability, and revision for large metal-on-metal (MoM) hip articulation. The literature for the North American experience is lacking. Purpose:. We report indications, short term outcomes, and complications of a series of subjects who received dual mobility outcomes at one institution. Study Design:. Consecutive subjects who received dual mobility total hip arthroplasty components from February 2010 and April 2013 were identified. Charts were retrospectively reviewed for surgical indications, comorbidities, component sizes, and perioperative complications including infection, dislocation, mechanical failure, and reoperation. Results:. 86 hips in 83 subjects underwent total hip arthroplasty or revision total hip arthroplasty using dual mobility components. There were 56 primary total hips and 30 revision total hips. Indications included small acetabular components in the setting of AVN (13 hips), DDH (12 hips) or severe inflammatory arthritis (5 hips), femoral neck fracture (5 hips), intraoperative instability (6 hips), recurrent postoperative instability (5 hips), and revision of large MoM articulations in the setting of failed hip resurfacing (10 hips) or failed MoM total hip arthroplasty (6 hips). Mean follow up was 1 year (3 months to 3.3 years). There were no complications in the primary total hip group. In the revision total hip group, only one hip dislocated and this was in a patient with familial dysautonomia and insensitivity to pain. One subject underwent reoperation for acute prosthetic joint infection. No other complications were encountered. Overall dislocation rate was 1.1% and overall complication rate was 2.2%. Conclusions:. These results closely mirror that of the European literature. Dual mobility articulations in total hip arthroplasty have a low short term complication rate in this cohort and provide a simple solution to difficult cases. Indications for these implants include primary and revision total hip arthroplasty in patients at high risk for instability and revision of large MoM implants including hip resurfacing

Background. Revision surgery for failed metal-on-metal (MOM) total hip arthroplasty (THA) or hip resurfacing (HR) has been a challenge. Previous studies have reported high failure and complication rates, including dislocation, infection, aseptic loosening and lower patient satisfaction. Options for revision depend on the integrity and stability of the femoral and acetabular components. When both components fail, full revision is required; however, when the acetabular component remains well fixed and oriented, only the isolated femoral component revision can be performed. Dual mobility components can be utilized to match the size to the inner diameter of the metal cup. With the dual mobility implant, the morbidity and complications associated with cup revision are avoided while maintaining a natural femoral head size and potentially increasing range of motion and stability postoperatively compared to standard THA. Purpose. The aim of this study was to evaluate short- to mid-term results of revision THA after failed metal-on-metal THA or HR using the dual mobility device. Study Design. Retrospective case series with prospective follow-up. Methods. A cohort of consecutive patients who underwent revision THA for failed MOM THA or HR utilizing a dual mobility device with a minimum follow-up of a year was identified. Charts were retrospectively reviewed for surgical indications, comorbidities, concomitant procedures, cup size, inner head size, outer head size, and perioperative complications, including infection, dislocation, mechanical failure and reoperation. Visual analogue pain scale (VAS), modified Harris Hip Score (mHHS) and SF-12 questionnaires were collected prospectively to assess functional outcomes after THA revision with a dual mobility component. Results. Fifteen consecutive patients (16 hips) underwent revision surgery utilizing a dual mobility component. Six hips were indicated for failed metal-on-metal THA and 10 for failed HR. The mean follow-up was 20 months (range, 12–29 months) and the mean VAS scores decreased from 8.9 preoperatively to 3.8 postoperatively (p < 0.01). The mean mHHS score increased from 26.9 preoperatively to 57.8 postoperatively (p < 0.05). A statistically significant improvement in the mean SF-12 scores was also noted (p < 0.05). Complications consisted of two patients with residual chronic pain. No dislocations, fractures, or infections were observed. Conclusion. Single component revision THA for failed MOM THA or HR utilizing a dual mobility device is an effective and relatively simple procedure for a complex problem

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 three 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 small retrospective series have shown satisfactory results for this indication at short- to medium-term follow-up times. However, there are important concerns with polyethylene wear, late intra-prosthetic 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. Until further long-term results are available, caution is advised in the routine use of dual mobility components in primary or revision total hip arthroplasty

Instability is the most common reason for revision after total hip arthroplasty (THA). Since THA requires arthrotomy of the hip and replacement with a femoral head that is smaller than the normal hip, instability following THA is always a potential concern. Many factors contribute to the development of instability after THA including: restoration of normal anatomy, implant design, component position, surgical approach and technique, and numerous patient related factors. Recently, the role of spinal mobility and deformity has been shown to have a significant effect on risk of dislocation after THA. The long held guidelines for component positioning or so called “safe zone” described by Lewinnek have also been questioned since most dislocations have been shown to occur in patients whose components are positioned within this “safe” range. In the early post-operative period, dislocation can occur prior to capsular and soft tissue healing if the patient exceeds their peri-operative range of motion limits. Closed reduction and abduction bracing for 6 weeks may allow for soft tissue healing and stabilization of the hip. It is important to try and identify the mechanism of dislocation since this can affect the technique of closed reduction, how the patient is braced following reduction and what may need to be addressed at the time of revision if dislocation recurs. Closed reduction and bracing may be effective in patients who have a previously well-functioning, stable THA who suffer a traumatic dislocation after the peri-operative period. Despite successful closed reduction, recurrent dislocation occurs in many patients and can be secondary to inadequate soft tissue healing, patient noncompliance or problems related to component positioning. Patients who incur more than 2 dislocations should be considered for revision surgery. Prior to revision surgery, an appropriate radiographic evaluation of the hip should be performed to identify any potential mechanical/kinematic issues that need to be addressed at the time of revision. Typically this involves plain radiographs, including a cross table lateral of the involved hip to assess acetabular version, but may also involve cross-sectional imaging to assess femoral version. Patients with soft tissue pseudotumors frequently have significant soft tissue deficiencies that are not amenable to component repositioning alone and require use of constrained or dual mobility components. In general, “limited revisions” consisting of modular head and liner exchange with insertion of a lipped liner and larger, longer femoral head rarely correct the problem of recurrent instability, since component malposition that frequently contributes to the instability is not addressed. Similarly, insertion of a constrained liner in a malpositioned cup is associated with a high rate of implant failure and recurrent dislocation since impingement contributing to the instability is not addressed. In patients who fail closed management and have a history of recurrent instability, we have found the treatment paradigm described by Wera, et al. to be very helpful in the management of the unstable THA. Several studies have shown that tripolar type constrained liners appear to perform considerably better than locking ring type constrained liners. As a result, dual mobility implants are becoming more widely utilised in patients with abductor and other soft tissue deficiencies, hip instability of uncertain etiology and patients with increased risk factors for instability undergoing primary THA. Early results with dual mobility components have been shown to have a low rate of failure in high instability risk revision THAs. These devices do have several unique potential complications and their use should be limited to patients with significantly increased risk of dislocation and instability

BACKGROUND. The most common salvage of a failed metal-on-metal hip resurfacing is to remove both the femoral and acetabular resurfacing components and perform a total hip replacement. The other choices are to perform an acetabular or femoral only revision. A one or two piece acetabular component or a polyethylene bipolar femoral component that matches the retained metal resurfacing acetabular component is used. The considerations in favor of performing a one component resurfacing revision are maintaining the natural femoral head size, limiting the surgical effort for the patient and surgeon, and bone conservation. There are often favorable cost considerations with single component revision surgery. The reasons for femoral component revision are femoral neck fracture, femoral component loosening and an adverse reaction to metal wear debris. Performing a femoral component only revision requires a well fixed and well oriented acetabular component. Acetabular revision is most often performed for an adverse reaction to metal wear debris or loosening. METHODS. 81 acetabular revisions and 46 femoral revisions were evaluated 4 to 14 years after surgery. 83% of patients had their initial surgery at outside institutions. The mean age was 46 and 65% of patients were women. A two piece titanium backed polyethylene component was used in 44 patients and a one or two piece metal component was used in 37. A dual mobility femoral prosthesis mated to a retained metal acetabular component was used for the femoral revisions and no conversions to a metal-on-metal total hip replacement were performed. We selected polyethylene acetabular components for patients with adverse reactions to metal wear debris if their femoral component was less than 48 mm or if there was no matching metal acetabular component available for their femoral component. We used dual mobility components for femoral loosening, femoral neck fractures and adverse reactions to metal wear debris in patients with well-fixed and well oriented metal acetabular components. Dual mobility components were also used if there are any concerns about the femoral component or in some older patients. We performed one component revisions rather than conversion to total hip replacement on 88% of patients presenting with failed resurfacing prostheses. RESULTS. There were no failures with polyethylene acetabular components. There were two failures due to ongoing adverse metal reactions in patients receiving metal revision acetabular components. There was one failure with a dual mobility prosthesis due to accelerated polyethylene wear from undetected edge loading on a retained worn metal acetabular component. There were two infections and one patient with continued pain. There were no dislocations. The average Harris Hip Score was 94. The UCLA activity score was 6 or greater for all but 4 patients. There were 6 revisions to total hip replacement. The Kaplan-Meier survivorship was 94%. 95% of patients rated their outcome as excellent or good. CONCLUSIONS. Failed metal-on-metal hip resurfacing prostheses can be successfully revised without conversion to total hip replacement in most instances. A detailed knowledge of matching prostheses is necessary. Polyethylene prostheses for the acetabular or femoral reconstruction are often needed

Dual mobility hip arthroplasty utilizes a freely rotating polyethylene liner to protect against dislocation. As liner motion has not been confirmed in vivo, we investigated the liner kinematics in vivo using dynamic radiostereometry. 16 patients with Anatomical Dual Mobility acetabular components were included. Markers were implanted in the liners using a drill guide. Static RSA recordings and patient reported outcome measures were obtained at post-op and 1-year follow-up. Dynamic RSA recordings were obtained at 1-year follow-up during a passive hip movement: abduction/external rotation, adduction/internal rotation (modified FABER-FADIR), to end-range and at 45° hip flexion. Liner- and neck movements were described as anteversion, inclination and rotation. Liner movement during modified FABER-FADIR was detected in 12 of 16 patients. Median (range) absolute liner movements were: anteversion 10° (5–20), inclination 6° (2–12), and rotation 11° (5–48) relative to the cup. Median absolute changes in the resulting liner/neck angle (small articulation) was 28° (12–46) and liner/cup angle (larger articulation) was 6° (4–21). Static RSA showed changes in median (range) liner anteversion from 7° (-12–23) postoperatively to 10° (-3–16) at 1-year follow-up and inclination from 42 (35–66) postoperatively to 59 (46–80) at 1-year follow-up. Liner/neck contact was associated with high initial liner anteversion (p=0.01). The polyethylene liner moves over time. One year after surgery the liner can move with or without liner/neck contact. The majority of movement is in the smaller articulation between head and liner

Dual mobility (DM) components are increasingly used to prevent and treat dislocation after total hip arthroplasty (THA). Intraprosthetic dissociation (IPD) is a known rare complication of these implants and has reportedly decreased with modern implants. The purpose of this paper is to report the diagnosis and treatment of modern DM IPD. 1453 DM components were implanted between 2010 and 2021. 695 in primary and 758 in revision THA. 49 hips sustained a dislocation of the large head and 5 sustained an IPD at presentation. 6 additional IPD occurred at the time of reduction of large head. The average age was 64, 54% were female and the mean follow-up was three years. Of the 11 IPD, 8 had a history of instability, 5 had abductor insufficiency, 4 had prior lumbar fusion, and 3 were conversions from fracture. The overall IPD incidence was 0.76%. Ten of the 11 DM IPD were missed at initial presentation or at the time of reduction, and all were discharged with presumed reduction. The mean time from IPD to surgical treatment was 3 weeks. One patient died with an IPD at 5 months. A DM head was reimplanted in six, two underwent revision of the acetabular component with exchange of DM head, and four were revised to a constrained liner. The re-revision rate was 55% at a mean 1.8 years. None of the patients who underwent cup revision required subsequent re-revision while half of the constrained liners and exchange of DM heads required re-revision. The overall rate of DM dislocation or IPD is low. It is critical to identify an IPD on radiographs as it was almost universally missed at presentation or when it occurred iatrogenically. For patients presenting with IPD, the surgeon should consider acetabular revision and conversion to a constrained liner or a larger DM, with special attention to removing impinging structures that could increase the risk of re-dislocation

The increased torque required to dislocate dual mobility (DM) components may increase peri-prosthetic femoral fracture (PPF) risk. Current literature often relies on revision as an endpoint and may underestimate PPF. This study aims to review PPF rate, risks and treatment following primary DM implantation. Prospective cohort study of 549 patients following primary DM total hip arthroplasty (THA) between 2013 and 2021. Collected data included demographics, indication for surgery, cortical index and PPF. 549 patients were identified with primary DM THA. Mean age was 73 years (26–96). 446 (81.2%) patients had their index surgery following hip fracture. 18 patients (3.27%) sustained a PPF. Cumulative PPF rate was 1.5% at 1-year, 2.2% at 5-years and 3.27% overall. PPF was higher in patients undergoing surgery following hip fracture (4%) vs. other indications (1%). OR 4.04 (95% CI:0.53, 30.72), p=0.219. Mean cortical index was lower in patients with PPF 0.4 (95% CI:0.36, 0.45) compared to those without 0.46 (95% CI:0.45, 0.46) p=0.029. Treatment for PPF included 10 (55.6%) open reduction internal fixation (ORIF), 7 (38.9%) revision THA and 1 conservatively managed. PPF rate following DM use is higher in our cohort than published rates. Our rates are comparable to some papers when subgroup analysis of older patients and cemented taper slip stems are considered. PPF risk with DM may be increased in patients undergoing surgery after hip fracture or with a lower cortical index preoperatively. Over half of PPF were managed with ORIF and may mask PPF risk studies that report using revision as an endpoint