No Difference in Force Required for Intraprosthetic Dislocation of Mixed Manufacturer vs Same Manufacturer Dual Mobility Articulations

Incidence, treatment, and outcomes of modern dual-mobility intraprosthetic dissociations

Aims

Dual-mobility (DM) components are increasingly used to prevent and treat dislocation after total hip arthroplasty (THA). Intraprosthetic dissociation (IPD) is a rare complication of DM that is believed to have decreased with contemporary implants. This study aimed to report incidence, treatment, and outcomes of contemporary DM IPD.

Methods

A total of 1,453 DM components were implanted at a single academic institution between January 2010 and December 2021: 695 in primary and 758 in revision THA. Of these, 49 presented with a dislocation of the large DM head and five presented with an IPD. At the time of closed reduction of the large DM dislocation, six additional IPDs occurred. The mean age was 64 years (SD 9.6), 54.5% were female (n = 6), and mean follow-up was 4.2 years (SD 1.8). Of the 11 IPDs, seven had a history of instability, five had abductor insufficiency, four had prior lumbar fusion, and two were conversions for failed fracture management.

Results

The incidence of IPD was 0.76%. Of the 11 IPDs, ten were missed either at presentation or after attempted reduction. All ten patients with a missed IPD were discharged with a presumed reduction. The mean time from IPD to surgical treatment was three weeks (0 to 23). One patient died after IPD prior to revision. Of the ten remaining hips with IPD, the DM head was exchanged in two, four underwent acetabular revision with DM exchange, and four were revised to a constrained liner. Of these, five (50%) underwent reoperation at a mean 1.8 years (SD 0.73), including one additional acetabular revision. No patients who underwent initial acetabular revision for IPD treatment required subsequent reoperation.

Conclusion

The overall rate of IPD was low at 0.76%. It is essential to identify an IPD on radiographs as the majority were missed at presentation or after iatrogenic dissociation. Surgeons should consider acetabular revision for IPD to allow conversion to a larger DM head, and take care to remove impinging structures that may increase the risk of subsequent failure.

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.

Predicting Instability Risk Following Hemiarthroplasty for Femoral Neck Hip Fractures in Geriatric Patients

BACKGROUND

Although a rare complication, dislocation following hemiarthroplasty (HA) for a femoral neck hip fracture is associated with increased mortality, readmission, and possible revision surgery. To date many of the specific risk factors have been difficult to demonstrate. Patient factors, surgical factors, as well as morphological factors need to be assessed. Therefore, the purpose of this study was to elucidate the risk factors for dislocation of HA following femoral neck hip fractures in the geriatric population.

METHODS

This was a retrospective review of 270 patients who had hip fractures. Medical records between the years 2016 and 2022 informed binomial regression predictive models. The discriminative ability of variables in the final model and acetabular anteversion to predict dislocation was assessed with area under the curve (AUC) estimates.

RESULTS

Center edge angle (odds ratio 1.23), abduction angle (odds ratio 1.17), and depth width ratio (2.96e-11) were significant predictors of dislocation (P = .003, .028, and <.001, respectively). Center edge angle and depth width ratio (<44.1 ° and .298), respectively, were cut scores for risk. Dementia had a high discriminative of ability, as did men (AUC = 0.617, 0.558, respectively). Acetabular anteversion was not predictive of dislocation (P = .259) and theorized anteversion safe zones had poor discriminative ability with AUCs of 0.510 and 0.503, respectively.

CONCLUSIONS

Morphological factors related to hip dysplasia and a shallow acetabulum, which can be assessed with a radiograph alone, were found to be predictors of instability following HA in the elderly. Hemiarthroplasty implant design and manufacturer, and also acetabular version did not contribute to instability 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.

Liner Dissociation and Acetabular Erosion Treated by Implant Retention and Dual-Mobility Liner Cementation: A Case Report

CASE

A 56-year-old woman underwent a left total hip arthroplasty (THA) after developing avascular necrosis after chemotherapeutic treatment of breast cancer. She presented approximately 2 years after index THA with left groin pain and complaints of instability. Imaging revealed pseudodislocation of the ceramic femoral head with erosion through the acetabular component. Intraoperative evaluation revealed a dissociated polyethylene liner, damaged acetabular locking mechanism, metallosis, and well-fixed and aligned components. Treatment consisted of component retention, bone grafting, and dual-mobility liner cementation into the acetabular component.

CONCLUSIONS

The two-year follow-up demonstrated a pain-free, well-functioning hip, bone graft incorporation, and no evidence of loosening.

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

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

Dual mobility cup in hip arthroplasty: an in-depth analysis of joint registries

Although total hip arthroplasty (THA) has shown successful results, instability remains a major complication. In recent years, dual mobility cups (DMC) have gained interest among clinicians thanks to its low rate of dislocation and good clinical results. The main aim of this work was to describe the accuracy of data on DMC from national and regional joint registries (JRs) and the available worldwide literature. We identified topics on DMC among JRs to propose a new harmonized and standardized section for DMC with the aim to understand its surveillance over the time. We extracted survival and implant data for a separate analysis. After performing a critical exclusion process, nine joint registries were considered eligible and included for final synthesis; these were the results from the available worldwide data from Joints Registries (JRs). In our study, eight analysed JRs reported a slight increase in DMC use in the last decade. In all the JRs evaluated and the available articles, dislocation remains one of the main reasons for revision and re-revision in hip arthroplasties. DMC is considered a valid construct increasingly used worldwide in primary and revision THA with the primary aim of reducing dislocation rates. Annual reports from JRs collect heterogeneous and low-quality information about outcomes and surveillance of DMC, creating a burden for clinicians to extract comparable data from different JR. Longer follow-up and a systematic registering of DMCs with international registry harmonization are needed to monitor DMC outcomes.

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

Introduction:

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

Materials and Methods:

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

Results:

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

Conclusion:

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