Can Dual Mobility Cups Reduce Revision and Dislocation Risks? An Analysis of 107,528 Primary Total Hip Arthroplasties in the United States.

BACKGROUND: Dual mobility acetabular cups (DMC) were designed to increase the effective femoral head size and improve stability with the goal of reducing revision risk at the potential cost of polyethylene thickness. We sought to evaluate revision risk following primary elective total hip arthroplasty with DMC compared to highly cross-linked polyethylene (XLPE). METHODS: A cohort study was conducted using data from a Kaiser Permanente's total joint arthroplasty registry. Patients ≥18 years who underwent primary elective total hip arthroplasty using DMC, unipolar Metal-on-XLPE (MoXLPE), or unipolar Ceramic-on-XLPE (CoXLPE) were identified (2010 to 2021). The final sample comprised 2,219 DMC, 48,251 MoXLPE, and 57,058 CoXLPE. Multiple Cox proportional hazard regressions were used to evaluate aseptic revision and any dislocation regardless of revision within 6 years follow-up. RESULTS: In adjusted analyses, no differences in aseptic revision risk were observed for MoXLPE (hazard ratio [HR] = 1.04, 95% confidence interval [CI] = 0.72 to 1.51) or CoXLPE (HR = 0.98, 95% CI = 0.69 to 1.40) compared to DMC. No differences in dislocation risk were observed for MoXLPE (HR = 1.42, 95% CI = 0.93 to 2.15) or CoXLPE (HR = 1.25, 95% CI = 0.84 to 1.87) compared to DMC. CONCLUSIONS: In a US-based cohort, 6-year aseptic revision risk of DMC was similar to metal or ceramic femoral head unipolar constructs. Furthermore, no difference in dislocation risk was observed. Continued longer-term follow-up may reveal if there is a reduced risk of dislocation that comes at the cost of increased late revision. LEVEL OF EVIDENCE: Level III.

Revision Dual Mobility Constructs With Unmatched Acetabular and Femoral Components Do Not Increase Failure Rate.

BACKGROUND: Dual mobility (DM) constructs for revision total hip arthroplasty (THA) have continued to grow in popularity to mitigate instability. This benefit comes at the cost of potential unique modes of failure, and there are theoretical concerns that combining femoral and acetabular components from different manufacturers could lead to increased failure rates. We aimed to investigate rates of reoperation between matched and unmatched DM implants used in revision THA. METHODS: We retrospectively reviewed 217 revision THAs performed with DM constructs between July 2012 and September 2021 at a single institution. Dual mobility (DM) constructs were classified as "matched" if the acetabular and femoral components were manufactured by the same company. They were classified as "unmatched" if the acetabular and femoral components were manufactured by different companies. The primary outcome was reoperation for any reason. RESULTS: There were 136 matched DM constructs and 81 unmatched constructs. Average follow-up was 4.6 years (range, 2.0 to 9.6 years). There was no difference in reoperation rate between matched and unmatched groups (11.0 versus 13.6%, P = .576). The most common reasons for reoperation in both groups were instability and periprosthetic joint infection. There was 1 revision for intraprosthetic dislocation in the matched group. CONCLUSIONS: The use of unmatched DM components in revision THA was common and did not increase the risk of reoperation at an average of 4.6-year follow-up. This information can be helpful in operative planning, but further research on long-term survival will be necessary.

Outcomes of Dual Mobility Versus Fixed-Bearing Components in Revision Total Hip Arthroplasty: A Systematic Review and Meta-Analysis.

BACKGROUND: Dual mobility (DM) implants have received increasing interest in revision surgery due to their increased stability. The aim of this systematic review was to compare outcomes of DM versus conventional fixed-bearing (FB) implants in revision total hip arthroplasty (rTHA). METHODS: A comprehensive search was performed using the PubMed, Embase, and MEDLINE databases between January 2000 and 2023. Outcome measures included rerevision due to dislocation, rerevision for other causes, all-cause rerevision, total complication rate, and functional outcome measures. The Methodological Index for Nonrandomized Studies assessment tool was used to evaluate methodological quality and the risk of bias. A pooled meta-analysis was conducted, with an assessment of heterogeneity using the Chi-square and Higgins I2 tests. A further subgroup analysis was performed between DM implants and larger femoral head (> 36 mm) FB implants. RESULTS: A total of 13 studies met the final inclusion criteria, with an overall number of 5,004 rTHA hips included (2,108 DM and 2,896 FB). The DM implants had significantly lower odds of rerevision due to dislocation (odds ratio [OR] 0.38, P < 0.001), aseptic loosening (OR 0.54, P = 0.004), and all-cause rerevision (OR 0.55, P < 0.001) compared to FB implants. No statistically significant difference was seen in the odds of rerevision due to periprosthetic joint infection (OR 0.99, P = 0.94) or periprosthetic fracture (OR 0.59, P = 0.13) between the 2 groups. The total number of complications showed an odds benefit in favor of DM implants (OR 0.43, P < 0.001). In the subgroup analysis, there was no significant difference in the odds of rerevision due to dislocation (OR 0.69, P = 0.11) between DM and larger femoral head FB implants. CONCLUSIONS: Based on current literature, it appears DM implants are an effective modality for reducing dislocation following rTHA with lower complication rates compared to FB implants. However, further prospective randomized controlled trials with longer term follow-up are required.

The Frank Stinchfield Award: Assembly and Dissociation Forces Differ Between Commonly Used Dual Mobility Implants: A Biomechanical Study.

BACKGROUND: Intraprosthetic dissociation (IPD) is a complication unique to dual mobility (DM) implants where the outer polyethylene head dissociates from the inner femoral head. Increasing reports of IPD at the time of closed reduction of large head DM dislocations prompted this biomechanical study evaluating the assembly and dissociation forces of DM heads. METHODS: We tested 17 polyethylene DM heads from 5 vendors. Of the heads, 12 were highly cross-linked polyethylene (4 vendors) and 5 were infused with vitamin E (2 vendors). Heads were between 46 and 47 mm in diameter, accepting a 28 mm-inner ceramic head. Implants were assembled and disassembled using a servohydraulic machine that recorded the forces and torques applied during testing. Dissociation was tested via both axial pull-out and lever-out techniques, where lever-out simulated stem-on-acetabular component impingement. RESULTS: The initial maximum assembly force was significantly different between all vendors (P < .01) and decreased for all implants with subsequent assembly. Vendor 4-E (Link with vitamin E) heads required the highest assembly force (1,831.9 ± 81.95 N), followed by Vendor 3 (Smith & Nephew), Vendor 5 (DePuy Synthes), Vendor 1-E (Zimmer Biomet with vitamin E), Vendor 2 (Stryker), and Vendor 1 (Zimmer Biomet Arcom). Vendor 4-E implants showed the greatest dissociation resistance in both pull-out (2,059.89 N, n = 1) and lever-out (38.95 ± 2.79 Nm) tests. Vendor 1-E implants with vitamin E required higher assembly force, dissociation force, and energy than Vendor 1 heads without vitamin E. CONCLUSIONS: There were notable differences in DM assembly and dissociation forces between implants. Diminishing force was required for assembly with each additional trial across vendors. Vendor 4-E DM heads required the highest assembly and dissociation forces. Vitamin E appeared to increase the assembly and dissociation forces. Based on these results, DM polyethylene heads should not be reimplanted after dissociation, and there may be a role for establishing a minimum dissociation energy standard to minimize IPD risk.

Dual Mobility Articulation in Total Hip Arthroplasty: Mixed Femoral and Acetabular Components are a Feasible Option.

BACKGROUND: The utilization of a different manufacturer for the prosthetic femoral head and the polyethylene insert in dual mobility (DM) for total hip arthroplasty (THA) may be necessary, especially in the revision setting. However, there is no data in the literature about this application. This study evaluated the outcomes of mixed manufacturer components, with the hypothesis that there would be no difference in measured outcomes compared to matched components. METHODS: The DM articulations implanted during THA revision were retrospectively reviewed from 2011 to 2017. The study group was then stratified into 2 cohorts: matching components or mixed components. Of 130 hips included in the study with DM articulations with average follow-up of 7 years, 103 had mixed and 27 had matching manufacturer components. Rates of all cause reoperation and revision, intraprosthetic dislocation, dislocation, and aseptic loosening were compared using Chi-squared and Fisher's exact test; survival analysis was also performed. RESULTS: Matched and mixed manufacturer implants had no significant difference between all cause reoperation (33 versus 25.2%), dislocation (14.8 versus 7.7%), and aseptic loosening (3.7 versus 3.9%), respectively. Higher rates of intraprosthetic dislocation (11 versus 0.97%) were observed in the matching component cohort. Survival analysis showed similar outcomes at 2, 5, and 10 years. CONCLUSIONS: Mixed-component DM articulations show similar results compared to matching components. The off-label use of mixed manufacture DM articulation in THA is a feasible and safe option in the correct patient. Furthermore, when encountering a well-fixed femoral stem or acetabular shell, the use of a mixed component DM articulations may reduce the morbidity for the patient and prevent revision of all components.

Fretting and Tribocorrosion of Modular Dual Mobility Liners: Role of Design, Microstructure, and Malseating.

BACKGROUND: Modular dual mobility (DM) bearings have a junction between a cobalt chrome alloy (CoCrMo) liner and titanium shell, and the risk of tribocorrosion at this interface remains a concern. The purpose of this study was to determine whether liner malseating and liner designs are associated with taper tribocorrosion. METHODS: We evaluated 28 retrieved modular DM implants with a mean in situ duration of 14.6 months (range, 1 to 83). There were 2 manufacturers included (12 and 16 liners, respectively). Liners were considered malseated if a distinct divergence between the liner and shell was present on postoperative radiographs. Tribocorrosion was analyzed qualitatively with the modified Goldberg Score and quantitatively with an optical coordinate-measuring machine. An acetabular shell per manufacturer was sectioned for metallographic analysis. RESULTS: There were 6 implants (22%) that had severe grade 4 corrosion, 6 (22%) had moderate grade 3, 11 (41%) had mild grade 2, and 5 (18.5%) had grade 1 or no visible corrosion. The average volumetric material loss at the taper was 0.086 ± 0.19 mm3. There were 7 liners (25%) that had radiographic evidence of malseating, and all were of a single design (P = .01). The 2 liner designs were fundamentally different from one another with respect to the cobalt chrome alloy type, taper surface finish, and shape deviations. Malseating was an independent risk factor for increased volumetric material loss (P = .017). CONCLUSIONS: DM tribocorrosion with quantifiable material loss occurred more commonly in malseated liners. Specific design characteristics may make liners more prone to malseating, and the interplay between seating mechanics, liner characteristics, and patient factors likely contributes to the shell/liner tribocorrosion environment. LEVEL OF EVIDENCE: Level III.

Some Offset Restoration Options Can Paradoxically Lead to Decreased Range of Motion in Primary Total Hip Arthroplasty: A 3-Dimensional Computer Simulation Study.

BACKGROUND: In total hip arthroplasty (THA), femoral offset restoration results in optimal biomechanics and range of motion (ROM) without bone-bone impingement. We hypothesized that differences in implant design features significantly affect bone-bone impingement risk in primary THA. METHODS: This retrospective computer simulation study included a cohort of 43 primary robotic arm-assisted THA. Considering sagittal pelvic tilt, we measured the maximum external rotation at 0° hip flexion and the maximum internal rotation at both 90° and 100° hip flexion before any bone-bone impingement occurred. To influence the offset, we included neutral or extended polyethylene liners, neutral or plus prosthetic heads, standard or high-offset stems, and stems with 132° or 127° neck angles. RESULTS: Extended polyethylene liner use resulted in decreased bone-bone impingement for both stems but also decreased prosthetic ROM in hip extension (mean -4.5 to 5°, range -10 to 0°) and hip flexion (mean -3 to 3.7°, range -10 to 0°) due to decreases in head diameter. Using a plus head or different stem offset/neck angle options resulted in either (1) no improvement in ROM (stem 1: 60%; stem 2: 28%) or (2) a paradoxical increase in bone-bone impingement (stem 1 with 127°: 19% and stem 2 with high offset option: 7%). CONCLUSION: Counterintuitively, a subset of patients experience a paradoxical increase in bone-bone impingement when transitioning from standard to high-offset or varus necks due to the pelvic and proximal femoral bone shape. For this group of patients, preoperative personalized 3-dimensional modeling may help guide implant choice for optimizing outcomes.

The use of dual mobility cups in revision total hip arthroplasty for failed large head metal-on-metal bearings.

PURPOSE: Revision of failed large head metal-on-metal (MoM) total hip arthroplasty (THA) is a challenging procedure particularly to reconstruct acetabular bone defect due to osteolysis and to achieve hip stability due to soft tissue damages, both potentially caused by adverse reaction to metal debris (ARMD). This study aimed to evaluate the outcome of dual mobility cup (DMC) constructs in revision THA for failed large head MoM bearings with a special attention to the occurrence of dislocation or re-revision. METHODS: Between 2015 and 2019, 57 patients (64 THAs, 41 men, mean age = 65 ± 10 years) underwent revision for MoM THA with the use of DMC were prospectively included in our total joint registry. Mean time to revision was 11 ± 2.5 years. The causes for revision were adverse reaction to metal debris (ARMD) in 49 THAs (76%), painful hip with elevated blood cobalt-chromium ions in seven (11%), and acetabular aseptic loosening in eight (13%). The revision was complete in 22 THAs (34%) and acetabular only in 42 (66%). Clinical and radiographic outcomes, complications, and re-revisions were evaluated at most recent follow-up. RESULTS: At mean follow-up of six ± 1.5 years, the pre- to postoperative Harris Hip Score improved from 74 ± 19 to 92 ± 4 (p = 0.004). Complications occurred in 11 cases (17%): five dislocations (8%), three periprosthetic infections (5%), two aseptic loosening of the acetabular component (3%), and two periprosthetic fractures (3%). Re-revision was required in six cases (9%). CONCLUSION: The use of DMC is a reliable option to prevent instability and ensure a stable acetabular reconstruction in revision THA for failed large head MoM bearings. However, dislocation after revision remains a concern, particularly in cases of severe soft tissue damage related to ARMD.

Intraoperative live measurement of femoral head size for acetabular cup sizing: simple, accurate, and green!

PURPOSE: Templating is the first step in achieving a successful total hip arthroplasty. We hypothesize that native head size is highly correlated with implanted cup size. Therefore, the purpose of this study is to look for a correlation between sizes of the intra-operative measurement of the femoral head and the implanted cup. METHODS: This is a monocentric observational study conducted from December 2018 till January 2023. All patients admitted for a primary total hip arthroplasty were included and retrospectively reviewed. Intra-operative femoral head measurement, radiographic femoral head diameter, templated (planned) cup size, and definitive implanted cup size were recorded. RESULTS: The sample included 154 patients (85 female and 69 males) with a mean age of 66.2 ± 10.4 years. There were 157 THA cases; 82 on the right side and 75 on the left side. The native head size and acetate template on digital radiographs were the most significantly positively correlated with cup size (P < 0.0001) while the radiological head size was significantly negatively correlated with cup size (P = 0.009). The implanted cup was on average 2 ± 2 mm bigger than the native head size measured intra-operatively. CONCLUSION: The native femoral head diameter measured intra-operatively is a simple and reliable tool to help the surgeons choose the proper size of the acetabular cup, preventing complications during surgery hence optimizing results post operatively. This technique would contribute to a more ecofriendly orthopaedic reconstructive surgery.

Dual-mobility tripod cup for revision hip arthroplasty: long-term (five to fourteen years) evaluation of a new generation cementless implant.

PURPOSE: The aims of this study were to evaluate the survivorships of a new generation cementless DMC with tripod additional fixation in revision total hip arthroplasty and complications at a minimum five year follow-up. METHODS: One hundred and fifteen revisions (THA) treated with tripod DMC performed between 2009 and 2015 were included in this retrospective study. Acetabular defects were classified as Paprosky 1 (n = 38, 33%), 2 (n = 75, 65%) or 3 (n = 2, 2%). Unipolar or bipolar revision was performed for the following indications: aseptic acetabular loosening (63%), infection (14%), aseptic bipolar loosening (11%), instability (4%), aseptic femoral loosening (3%), ALVAL (3%) and iliopsoas impingement (2%). Mean follow-up was 9.4 years ± two (range, 5 to 14). RESULTS: At the final follow-up, a single episode of dislocation occurred within three months after the procedure (0.8%) with no revision. Three cases of aseptic loosening were diagnosed (2.6%). Four infections (3.5%) required reoperation: three required a two stage bipolar revision; one was treated by DAIR procedure. At the latest follow-up, the survivorship of the acetabular cup for aseptic loosening was 98% [95% CI (91.2-99.4)] and for any reasons was 94.4% [95% CI (90.1%-98.9%)]; the mean HHS improved from 60 points (range, 18-94 points) to 83 points (range, 37-100 points) (p < .001). CONCLUSION: This study reports a low complication rate in favour of the use of a tripod DMC in revision THA with a satisfactory survivorship at a ten year follow-up.

Short-term primary and revision modular dual-mobility cup total hip arthroplasty outcomes in high-risk dislocation patients: a retrospective study.

PURPOSE: Modular dual-mobility cups (MDMCs) have a lower risk for dislocation after total hip arthroplasty (THA). The primary aims of our study were to analyze implant survivorship and to determine complications, especially dislocation, and revision rates of primary THAs used for hip fracture patients and for revision THAs. Secondary aims were to evaluate mortality after MDMC surgery and to find out if introduction of MDMC at our institution (Kuopio University Hospital, Finland) have decreased dislocation rate. METHODS: This retrospective cohort study consisted of 101 MDMC patients who were consecutively operated at our institution between April 1, 2018 and June 30, 2020. The implant survival rate, complications and mortality were evaluated with minimum of 2-year follow-up. Finnish Hospital Discharge Register was used to find out yearly dislocation rates following THA at our institution. RESULTS: The cumulative estimate implant survival after MDMC in the primary THA group was 97% at 2 years, and in the revision THA group, it was 90% at 2 years. Dislocation was a rare complication in the primary THA group (1.4%), while it was common in revision THA group (12.9%). The cumulative estimate for mortality after MDMC in the primary THA group was 13% at 2 years, and in the revision group, it was also 13% at 2 years. The yearly number of patients who had re-hospitalization period due to THA dislocation decreased 46% after implementation of MDMC. CONCLUSION: Short-term survival and complication rates after MDMC were excellent after primary THA and moderate after revision THA. Implementation of MDMC THA for hip fracture patients seems to have effectively decrease dislocation rate during a short follow-up.

Medium-term outcome of the Libra® cemented versus cementless stems in primary dual mobility total hip arthroplasty.

INTRODUCTION: Despite the increasing use of cementless stems in total hip arthroplasty, the cemented stem has played a valuable role in the armamentarium of orthopedic surgeons. This study aims to compare two types of Libra® stems SERF, one cemented (Libra® C) and the other cementless hydroxyapatite coated (Libra® HA) that were conducted to analyze the medium-term outcome regarding their behavior and longevity. METHODS: This is a retrospective study for patients who received primary total hip arthroplasty with Dual Mobility (DM) articulation in the period between January 2014 to January 2020 with a minimum of two years follow-up. Two-hundred hips have been identified in 196 patients. One hundred forty-three Libra® cementless versus fifty-seven Libra cemented stems were implanted and the outcome of these stems is reported. All procedures were performed through the posterior approach and cemented stems were selected for elderly patients with wide medullary canals Dorr Type C. The indications for the index procedure were fractures, avascular necrosis, rheumatoid, and osteoarthritis. One hundred thirty-nine cementless DM cups were used while sixty-one hips had cemented Novae stick cups. Radiological evaluation for cup and stem positions, cement mantle, and radiolucent lines was performed, besides clinical function using the Harris Hip Score. RESULTS: The average age of patients was 60 ± 14.8. At the latest review, none of the cemented stems was revised or awaiting revision. One cementless stem was revised because of cortical perforation. Five intraoperative fractures were observed in the cementless group, but none of them needed revision or affected the stem stability. Readmission to theatre occurred in four patients to evacuate hematoma in two, a reduction of dislocation in one, and grafting bone lysis in one. CONCLUSION: Cemented stems have an important role in osteoporotic patients with wide medullary canals with excellent outcomes and minimal risk of fracture. LEVEL OF EVIDENCE: Level IV.

Malseating of Modular Dual Mobility Liners: High Prevalence in Revision Total Hip Arthroplasty.

BACKGROUND: Modular dual mobility (MDM) acetabular components have become increasingly more popular in total hip arthroplasty (THA). Uncertainty remains regarding liner malseating and its consequences after 5 to 10 years, especially in patients who undergo revision THA. The objective of this study was to analyze the prevalence of malseating and implant survivorship of patients who underwent revision THA using an MDM liner. METHODS: We retrospectively identified patients who had a minimum 2-year follow-up and underwent revision THA using an MDM liner. Patient demographics, implant details, mortality, and all-cause revisions were recorded. Patients who had radiographic follow-up were assessed for malseating. Kaplan-Meier survival was used to determine implant survivorship. We included 143 hips in 141 patients. Mean age was 70 years (35-93 years), and 86 patients (60.1%) were female. RESULTS: Overall implant survival was 89.3% (95% confidence interval (CI) 0.843-0.946) at a mean follow-up of 6 years (ranging from 2 to 10 years). There were eight patients excluded from malseating assessment. Upon radiological review, 15 liners (11.1%) were malseated. Survival for all-cause revision for patients with malseated liners was 80.0% (12/15, 95% CI 0.62 - 0.99, P = .15) versus 91.5% in patients who had nonmalseated liners (110/120, 95% CI 0.86-0.96). There were no intraprosthetic dislocations and 3.5% of the patients were revised due to instability. No liners were revised due to malseating, and no patients who had malseated liners were revised due to instability. CONCLUSIONS: Using MDM components in our cohort comprised of revision THA was associated with a high prevalence of malseating and an overall survival of 89.3% at a mean follow-up of 6 years. Malseating does not appear to impact implant survival at a mean follow-up of 6 years.

Radiographic Accuracy of Malseated Dual-Mobility Liners Varies Based on Implant Design.

BACKGROUND: Dual-mobility constructs have gained popularity to mitigate dislocations after high-risk primary and revision total hip arthroplasties. Contemporary data have indicated that malseating of modular dual-mobility liners occurs in up to 6% of cases. The purpose of this cadaveric-based radiographic study was to determine the ability to accurately determine if modular dual-mobility liners were seated. METHODS: There were 10 hips (5 cadaveric pelvic specimens) used to implant modular dual-mobility liners of 2 designs. One had a liner that seated flush and the other had an extended rim. There were 20 constructs that were well-seated and 20 constructs were intentionally malseated. A comprehensive series of radiographs was reviewed by 2 blinded surgeons. Statistical analyses included Chi-squared testing, logistic regressions, and kappa statistics. RESULTS: Radiographic assessment of liner malseating was not accurate with an elevated rim design with misdiagnosis in 40% (16 of 40). The flush design had diagnostic errors in 5% (2 of 40; P = .0002). Logistic regressions demonstrated a significantly higher risk of misdiagnosing a malseated liner in the elevated rim group (odds ratio 13). There were 12 of 16 misdiagnoses in the elevated rim group failing to recognize a malseated liner. Each surgeon had almost perfect agreement for intraobserver reliability for flush designs (k 0.90) and fair agreement in the elevated rim design (k 0.35). CONCLUSION: A comprehensive series of plain radiographs can reliably detect a malseated modular dual-mobility liner with a flush rim design in 95% of cases. However, elevated rim designs are more difficult to accurately identify malseating on plain radiographs.

Polyethylene Dual Mobility Liners Show Minimal Polyethylene Changes in Early Retrievals.

BACKGROUND: Dual mobility (DM) liners were introduced to reduce instability in total hip arthroplasty. They were found to allow for motion predominantly at the femoral head and the inner bearing of the acetabular liner; however, little is known if this motion is sufficient to alter polyethylene material characteristics. We assessed cross-link (XL) density and oxidation index (OI) measurements of the inner and outer bearing articulations. METHODS: Thirty-seven DM liners were collected with a duration of implantation greater than 2 years. Clinical and demographic data were collected from a chart review. A cylinder was cored from the apex of each liner and cut into 4.5 mm long inner and outer diameter segments for XL density swell ratio testing. The OI was measured from sagittal 100 µm microtome slices using Fourier transform infrared spectroscopy. Student's t-tests were used to determine differences in OI and XL density between the bearings. Spearman's correlation assessed relationships between patient demographics, OI, and XL density. Duration of implantation for the cohort was a mean of 35 (range, 24-96) months. RESULTS: The inner and outer bearing had similar median XL densities (0.17 mol/dm3 versus 0.17 mol/dm3, P = .6). The inner bearing had an increased OI when compared to the outer bearing (0.16 versus 0.13, P = .008). The OI was inversely correlated with XL density (r = -0.50, P = .002). CONCLUSION: Small differences were found in oxidation between the inner and outer bearing of the DM construct. Failures at an average of 3 years indicate low levels of oxidation, unlikely to impact the mechanical properties of the material.

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

BACKGROUND: Cemented dual mobility cups (DMCs) are commonly used in combination with acetabular reinforcement devices. Indeed, according to literature, direct cementation of metal-backed acetabular components into the bony acetabulum remains controversial as this technique is potentially associated with increased rates of aseptic loosening. Therefore, this study aimed to evaluate the clinical and radiographic outcomes of DMC cemented into the bony acetabulum in primary total hip arthroplasty (THA). METHODS: A total of 49 THA (48 patients, mean age 78 years [range, 51 to 91]) performed with direct cementation of a DMC into the bony acetabulum were prospectively included in our total joint registry and retrospectively reviewed. The clinical outcome was assessed using the Harris hip score (HHS). The radiographic outcome included measurement of component positioning and occurrence and progression of demarcation around the cemented DMC. Complications were reported with a particular attention to cemented fixation failure and aseptic loosening. RESULTS: At a 7-year mean follow-up (range, 5 to 8), the pre-to postoperative HHS improved from 47 (range, 30 to 58) to 92 points (range, 80 to 98) (P < .01). Nonprogressive and focalized demarcations were observed in 7 THA (14%). Importantly, no progressive demarcation or DMC aseptic loosening was observed. CONCLUSION: Direct cementation of DMC into the bony acetabulum ensured a stable fixation with no progressive demarcation or aseptic loosening at midterm follow-up. Therefore, this technique can be selectively considered in primary THA, especially in elderly or frail patients to avoid potential mechanical failure of press-fit fixation due to altered bone quality or additional morbidity related to the use of acetabular reinforcement devices.

A Meta-Analysis of the Incidence and Temporal Trends of Postoperative Dislocation in Revision Total Hip Arthroplasty Utilizing Constrained Acetabular Components or Dual Mobility Implants.

BACKGROUND: The incidence of dislocation after revision total hip arthroplasty (rTHA) is reported to be up to 25% and remains a common source of failure. Constrained acetabular components and dual mobility implants are two implant classes being utilized to alleviate this burden in patients who have recurrent instability or major intraoperative instability. This meta-analysis evaluated the incidence and temporal trends of dislocation after implantation with constrained acetabular components and dual mobility implants in rTHA. METHODS: Longitudinal studies reporting dislocation after the use of constrained acetabular components or dual mobility implants in rTHA were sought from Medline and Embase to October 2022. Secondary outcomes included re-revision surgery for dislocation and all causes. A total of 75 relevant citations were identified comprising 36 datasets of 3,784 constrained acetabular components and 47 datasets of 10,216 dual mobility implants. RESULTS: For constrained acetabular components, the pooled incidence of dislocation was 9% (95% confidence interval: 7.2, 11.7) (range 0.0%-35.3%) over a weighted mean follow-up of 6 years, in contrast to 3% (95% confidence interval: 2.2, 4.4) (range 0.0%-21.4%) over 5 years for dual mobility implants. Re-revision rates for dislocation after using constrained acetabular components were around 9%, in contrast to 2% for dual mobility implants. Re-revision rates for all causes after using constrained acetabular components were around 19%, in contrast to 8% for dual mobility implants. CONCLUSION: Dual mobility implants in the context of rTHA demonstrate lower incidences of dislocation (3% versus 9%), re-revision for dislocation (2% versus 9%), and rer-evision for any cause (8% versus 19%) in contrast to constrained acetabular components. This must be considered by surgeons when implanting such devices, often selected to treat instability.

Posterior Approach Total Hip Arthroplasty Utilizing a Monoblock Dual-Mobility Construct Without Posterior Hip Precautions: A Series of 580 Hips With One Dislocation.

BACKGROUND: Instability remains a devastating complication following total hip arthroplasty. Here we describe a mini-posterior approach with a monoblock dual-mobility implant without "traditional posterior hip precautions" yielding excellent results. METHODS: There were 580 consecutive hips in 575 patients who underwent total hip arthroplasty utilizing a monoblock dual-mobility implant and a mini-posterior approach. With this technique, the acetabular component positioning does not rely on tradition intra-operative radiographic abduction and anteversion goals but rather uses patient-specific anatomic landmarks (anterior acetabular rim and, when visible, the transverse acetabular ligament) to set cup position; stability is assessed with a significant, dynamic intra-operative test of range of motion. Patients' mean age was 64 years (range, 21 to 94), and 53.7% were women. RESULTS: Mean abduction was 48.4° (range, 29° to 68°) and mean anteversion was 24.7° (range, -1° to 51°). Patient Reported Outcomes Measurement Information System scores improved in every measured domain from preoperative to final postoperative visit. There were seven (1.2%) patients who required reoperation, with mean time to reoperation of 1.3 months (range, one to 176 days). Only one patient (0.2%) who had a preoperative history of spinal cord injury and Charcot arthropathy dislocated. CONCLUSION: A posterior approach hip surgeon may want to consider using a monoblock dual-mobility construct and avoidance of traditional posterior hip precautions to achieve early hip stability with an extremely low dislocation rate and high patient satisfaction scores.

Dual-Mobility versus Large Femoral Heads in Revision Total Hip Arthroplasty: Interim Analysis of a Randomized Controlled Trial.

BACKGROUND: This multicenter randomized controlled trial evaluated if dual-mobility bearings (DM) lower the risk of dislocation compared to large femoral heads (≥36 mm) for patients undergoing revision total hip arthroplasty (THA) via a posterior approach. METHODS: A total of 146 patients were randomized to a DM (n = 76; 46 mm median effective head size, range 36 to 59 mm) or a large femoral head (n = 70; twenty-five 36 mm heads [35.7%], forty-one 40 mm heads [58.6%], and four 44 mm heads [5.7%]). There were 71 single-component revisions (48.6%), 39 both-component revisions (26.7%), 24 reimplantations of THA after 2-stage revision (16.4%), seven isolated head and liner exchanges (4.8%), four conversions of hemiarthroplasty (2.7%), and 1 revision of a hip resurfacing (0.7%). Power analysis determined that 161 patients were required in each group to lower the dislocation rate from 8.4 to 2.2% (power = 0.8, alpha = 0.05). RESULTS: At a mean of 18.2 months (range, 1.4 to 48.2), there were three dislocations in the large femoral head group compared to two in the DM cohort (4.3 versus 2.6%; P = .67). One patient in the large head group and none in the DM group were successfully treated with closed reduction without subsequent revision. CONCLUSION: Interim analysis of this randomized controlled trial found no difference in the risk of dislocation between DM and large femoral heads in revision THA, although the rate of dislocation was lower than anticipated and continued follow-up is needed.

Dual Mobility Articulation in Revision Total Hip Arthroplasty: An American Joint Replacement Registry Analysis of Patients Aged 65 Years and Older.

BACKGROUND: Increasingly, dual mobility (DM) articulations have been used in revision total hip arthroplasty (THA), which may prevent postoperative hip instability. The purpose of this study was to report on outcomes of DM implants used in revision THA from the American Joint Replacement Registry (AJRR). METHODS: Revision THA cases performed between 2012 and 2018 Medicare were eligible and categorized by 3 articulations: DM, ≤32 mm, and ≥36 mm femoral heads. The AJRR-sourced revision THA cases were linked to Centers for Medicare and Medicaid Services (CMS) claims data to supplement (re)revision cases not captured in the AJRR. Patient and hospital characteristics were described and modeled as covariates. Using multivariable Cox proportional hazard models, considering competing risk of mortalities, hazard ratios were estimated for all-cause re-revision and re-revision for instability. Of 20,728 revision THAs, 3,043 (14.7%) received a DM, 6,565 (31.7%) a ≤32 mm head, and 11,120 (53.6%) a ≥36 mm head. RESULTS: At 8-year follow-up, the cumulative all-cause re-revision rate for ≤32 mm heads was 21.9% (95%-confidence interval (CI) 20.2%-23.7%) and significantly (P < .0001) higher than DM (16.5%, 95%-CI 15.0%-18.2%) and ≥36 mm heads (15.2%, 95%-CI 14.2%-16.3%). At 8-year follow-up, ≥36 heads had significantly (P < .0001) lower hazard of re-revision for instability (3.3%, 95%-CI 2.9%-3.7%) while the DM (5.4%, 95%-CI 4.5%-6.5%) and ≤32 mm groups (8.6%, 95%-CI 7.7%-9.6%) had higher rates. CONCLUSION: The DM bearings are associated with lower rates of revision for instability compared to patients who had ≤32 mm heads and higher revision rates for ≥36 mm heads. These results may be biased due to unidentified covariates associated with implant selection.