Adverse Local Tissue Reaction due to Acetabular Corrosion in Modular Dual-Mobility Constructs

Are Corrosion and Material Loss a Threat for Titanium-Titanium Tapers in Total Hip Arthroplasty Modular Acetabular Components?

BACKGROUND

Extensive research has reported on fretting corrosion and material loss for a variety of metal taper interfaces in orthopedic devices. For modular acetabular shell-liner constructs, the interfaces studied thus far have consisted of mixed-metal pairings, and the risk of fretting corrosion and material loss for the all-titanium (Ti) shell-liner taper junction in one ceramic-on-ceramic (COC) design remains poorly understood. We asked: do Ti shell-liner taper interfaces in COC total hip arthroplasty devices show in vivo evidence of (1) fretting and/or corrosion, and (2) quantifiable potential material loss?

METHODS

We examined 22 shell-liner pairs and 22 single liners from retrieved COC components. The taper interface surfaces were assessed for fretting corrosion using a semiquantitative scoring method and imaged with scanning electron microscopy. A subcohort of components was measured with a coordinate measuring machine, and volumetric material loss and maximum wear depth were calculated.

RESULTS

Fretting corrosion at the taper interfaces was minimal to mild for 95% of liners and 100% of shells. Imaging revealed fretting marks within a band of corrosion on some implants and evidence of corrosion not in the proximity of mechanical damage. Estimated material loss ranged from 0.2 to 1.3 mm3 for liners, and 0.5 to 1.1 mm3 for shells. Maximum wear depth for all components was 0.03 mm or less.

CONCLUSIONS

Our results indicate that, compared to other taper junctions in total joint arthroplasty, the risk of corrosion and material loss may be minimal for Ti shell-liner interfaces.

Decreased Instability in High-Risk (Hip-Spine 2B) Patients After Modifications of Surgical Planning and Technique

BACKGROUND

Patients undergoing primary total hip arthroplasty (THA) who have spinal deformity and a stiff spine are the highest-risk group for instability. Despite the increasing use of dual-mobility cups and large femoral heads, dislocation remains a major complication after THA. Preoperative planning becomes a critical aspect of ensuring precise component positioning within a safe zone. The purpose of this study was to investigate dislocation rates over a 9-year period.

METHODS

A retrospective review of 4,731 THAs performed by 3 orthopaedic surgeons between January 2014 and March 2023 was performed. Spinopelvic measurements were conducted to determine the hip-spine classification group for each patient. Only patients classified as 2B (pelvic incidence-lumbar lordosis > 10° and Δsacral slope < 10°) were eligible. Both absolute and relative dislocation frequencies were then analyzed using time-series analysis techniques and Fisher's exact tests.

RESULTS

A total of 281 hip-spine 2B patients undergoing primary THA were eligible for analysis (57% women; mean age, range: 66 years, 23 to 87; mean body mass index, range: 28, 16 to 45). The overall dislocation rate was 4.3%. Use of femoral head sizes ≥ 40 mm increased from 4% in 2014 to 2019 to 37% in 2020 to 2023 (P < .001), while the use of dual-mobility cups decreased from 100% in 2014 to 2019 to 37% in 2020 to 2023 (P < .001). Acetabular component planning was changed from the supine plane to the standing plane in February 2020. Those changes in surgical practice were notably correlated with a significant decrease in dislocation rates from 6.8% in 2014 to 2019 to 1.5% in 2020 to 2023 (P = .03).

CONCLUSIONS

Our study demonstrates that the introduction of advanced preoperative THA planning to the standing plane, coupled with precise intraoperative technology for implant placement, can significantly reduce the risk of instability in high-risk THA patients. Notably, we observed a significant decrease in dislocation rates, which aligned with the shift in surgical practice.

LEVEL OF EVIDENCE

IV.

Cemented dual-mobility constructs in uncemented revision acetabular components

Aims

Dislocation remains a leading cause of failure following revision total hip arthroplasty (THA). While dual-mobility (DM) bearings have been shown to mitigate this risk, options are limited when retaining or implanting an uncemented shell without modular DM options. In these circumstances, a monoblock DM cup, designed for cementing, can be cemented into an uncemented acetabular shell. The goal of this study was to describe the implant survival, complications, and radiological outcomes of this construct.

Methods

We identified 64 patients (65 hips) who had a single-design cemented DM cup cemented into an uncemented acetabular shell during revision THA between 2018 and 2020 at our institution. Cups were cemented into either uncemented cups designed for liner cementing (n = 48; 74%) or retained (n = 17; 26%) acetabular components. Median outer head diameter was 42 mm. Mean age was 69 years (SD 11), mean BMI was 32 kg/m2 (SD 8), and 52% (n = 34) were female. Survival was assessed using Kaplan-Meier methods. Mean follow-up was two years (SD 0.97).

Results

There were nine cemented DM cup revisions: three for periprosthetic joint infection, three for acetabular aseptic loosening from bone, two for dislocation, and one for a broken cup-cage construct. The two-year survivals free of aseptic DM revision and dislocation were both 92%. There were five postoperative dislocations, all in patients with prior dislocation or abductor deficiency. On radiological review, the DM cup remained well-fixed at the cemented interface in all but one case.

Conclusion

While dislocation was not eliminated in this series of complex revision THAs, this technique allowed for maximization of femoral head diameter and optimization of effective acetabular component position during cementing. Of note, there was only one failure at the cemented interface.

Removing Cemented Dual Mobility Liners From Acetabular Components: A Technical Tip for a Challenging Surgical Problem

Dislocation remains the leading cause of failure following revision total hip arthroplasty. Dual mobility (DM) constructs, including monoblock cups designed for cementation, reduce but do not eliminate this risk. Cemented DM constructs offer several unique advantages in revision total hip arthroplasty, and as such, they have gained popularity. Despite their advantages, a portion of these implants will require revision for infection or recurrent dislocation. Removal of a cemented DM cup presents numerous challenges, and there is no effective published technique. Here, we present an effective technique for the safe removal of one design of cemented DM cup.

Evolution and New Generation of Dual Mobility Cups

Although total hip arthroplasty (THA) is considered a successful procedure, hip dislocation remains the main cause of early failure. Dual mobility cups (DMCs) have been shown to significantly reduce the dislocation rate in both primary and revision THAs. During the past several decades, DMCs have evolved in design and fixation interface. There have been three generations of DMCs. This article addresses the rationale for a new cementless highly porous titanium DMC to improve component fixation and implant biocompatibility. [Orthopedics. 2023;46(5):e273-e280.].

Large Femoral Heads and Select Dual-Mobility Bearings Are Associated With Reduced Instability in Contemporary Posterior Approach Total Hip Arthroplasty

BACKGROUND

Postoperative dislocation is considered the main drawback of posterior approach total hip arthroplasty (THA). Thinner highly cross-linked polyethylene and dual-mobility bearings allow maximizing femoral head diameter per a given cup size. This study evaluated dislocation rates as large femoral head bearings were introduced into a practice over an 11-year period.

METHODS

A total of 1,511 consecutive primary THAs were retrospectively reviewed. Demographics, implant sizes, femoral head-acetabular cup ratio, and dislocation status were collected from the electronic medical record. Data were evaluated using time series analysis techniques as larger femoral heads, thinner polyethylene liners, and dual-mobility bearings were introduced. The cohort was 57% women with mean age and body mass index of 62 years (range, 13 to 93) and 31 kg/m² (range, 13 to 54), respectively.

RESULTS

The overall dislocation rate was 0.98%. Use of femoral head sizes ≥ 40 millimeters increased from 4% in the years 2010 to 2016 to 51% in the years 2017 to 2021, correlating with a 50% reduction in dislocation rate from 1.4% to 0.7% (P = .279). Also, no dislocations occurred in patients who had dual-mobility bearings or ≥ 40-millimeter femoral heads (P = .007). Twelve of 14 dislocations occurred in cases with head-cup ratio < 0.7 (P = .013). Thirteen of 14 dislocations were in women (P = .005).

CONCLUSION

Maximizing the femoral head diameter per given cup size correlated with a decrease in dislocation rate in modern posterior approach THA. Furthermore, these results suggest that dual-mobility articulations should be reserved for high-risk patients or patients in whom a 40-millimeter femoral head is not possible.

LEVEL OF EVIDENCE

IV-consecutive case series; no control group.

The Role of Dual-Mobility Components in Total Hip Arthroplasty

➤

Dual mobility (DM) refers to a now widely available option for total hip articulation. DM implants feature a small inner head, a hard bearing, that connects via a taper fit onto the femoral trunnion. This head freely rotates but is encased inside a larger, outer polyethylene head that articulates with a smooth acetabular component.

➤

DM acetabular components are available in the form of a monoblock shell or as a liner that is impacted into a modular shell, providing a metal articulation for the polyethylene outer head.

➤

DM is designed to increase hip stability by providing the arthroplasty construct with a higher jump distance, head-to-neck ratio, and range of motion prior to impingement.

➤

The use of DM in total hip arthroplasty continues to increase in the United States for both primary and revision arthroplasty. Surgeons should be aware of the potential benefits and pitfalls.

➤

Long-term data are lacking, especially for modular DM implants. Points of concern include a potential for accelerated polyethylene wear, intraprosthetic dislocation, and modular backside fretting corrosion.

Minimum Five-Year Outcomes of Modular Dual Mobility in Primary Total Hip Arthroplasty

BACKGROUND

Using a modular dual-mobility (MDM) bearing in primary total hip arthroplasty (THA) has not been widely evaluated. The purpose of this study is to evaluate clinical outcomes and survivorship following MDM bearings in primary THA.

METHODS

We used our registry database for patients with an MDM bearing on primary THA, performed by 6 surgeons through supine direct lateral or direct anterior approach. MDM bearings were used most often when impingement or subluxation was present intraoperatively despite proper component position. Another indication was a patient with planned activities who might be at a higher risk of instability postoperatively.

RESULTS

A total of 127 MDM bearings were used in primary THA in 119 patients. Mean follow-up was 6.77 years (range 5-8.9). Five hips were revised, none of which were due to MDM bearing failure. Preoperative Hip dysfunction and Osteoarthritis Outcome Score for Joint Replacement, Veterans RAND/Short Form 12 Physical Health Score and Mental Health Score increased from 25.81 to 52.40 (P < .0001), 30.42 to 44.50 (P < .0001), and 36.21 to 52.70 (P < .0001) at latest completed survey follow-up, respectively.

CONCLUSION

This MDM bearing shows excellent functional outcomes at a minimum 5 years of follow-up with no bearing-related failures. It can be an excellent choice in primary THA specifically in females where the use of increased head size to prevent instability is not possible due to anatomical restrictions and liner thickness.

In Revision THA, Is the Re-revision Risk for Dislocation and Aseptic Causes Greater in Dual-mobility Constructs or Large Femoral Head Bearings? A Study from the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

Dislocation is one of the most common causes of a re-revision after a revision THA. Dual-mobility constructs and large femoral head bearings (≥ 36 mm) are known options for mitigating this risk. However, it is unknown which of these choices is better for reducing the risk of dislocation and all-cause re-revision surgery. It is also unknown whether there is a difference between dual-mobility constructs and large femoral head bearings according to the size of the acetabular component.

QUESTIONS/PURPOSES

We used data from a large national registry to ask: In patients undergoing revision THA for aseptic causes after a primary THA performed for osteoarthritis, (1) Does the proportion of re-revision surgery for prosthesis dislocation differ between revision THAs performed with dual-mobility constructs and those performed with large femoral head bearings? (2) Does the proportion of re-revision surgery for all aseptic causes differ between revision THAs performed with dual-mobility constructs and those performed with large femoral head bearings? (3) Is there a difference when the results are stratified by acetabular component size?

METHODS

Data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) were analyzed for 1295 first-revision THAs for aseptic causes after a primary THA performed for osteoarthritis. The study period was from January 2008-when the first dual-mobility prosthesis was recorded-to December 2019. There were 502 dual-mobility constructs and 793 large femoral head bearings. There was a larger percentage of women in the dual-mobility construct group (67% [334 of 502]) compared with the large femoral head bearing group (51% [402 of 793]), but this was adjusted for in the statistical analysis. Patient ages were similar for the dual-mobility construct group (67 ± 11 years) and the large femoral head group (65 ± 12 years). American Society of Anesthesiologists (ASA) class and BMI distributions were similar. The mean follow-up was shorter for dual-mobility constructs at 2 ± 1.8 years compared with 4 ± 2.9 years for large femoral head bearings. The cumulative percent revision (CPR) was determined for a diagnosis of prosthesis dislocation as well as for all aseptic causes (excluding infection). Procedures using metal-on-metal bearings were excluded. The time to the re-revision was described using Kaplan-Meier estimates of survivorship, with right censoring for death or database closure at the time of analysis. The unadjusted CPR was estimated each year of the first 5 years for dual-mobility constructs and for each of the first 9 years for large femoral head bearings, with 95% confidence intervals using unadjusted pointwise Greenwood estimates. The apparent shorter follow-up of the dual-mobility construct group relates to the more recent increase in dual-mobility numbers recorded in the registry. The results were adjusted for age, gender, and femoral fixation. Results were subanalyzed for acetabular component sizes < 58 mm and ≥ 58 mm, set a priori on the basis of biomechanical and other registry data.

RESULTS

There was no difference in the proportion of re-revision for prosthesis dislocation between dual-mobility constructs and large femoral head bearings (hazard ratio 1.22 [95% CI 0.70 to 2.12]; p = 0.49). At 5 years, the CPR of the re-revision for prosthesis dislocation was 4.0% for dual mobility constructs (95% CI 2.3% to 6.8%) and 4.1% for large femoral head bearings (95% CI 2.7% to 6.1%). There was no difference in the proportion of all aseptic-cause second revisions between dual-mobility constructs and large femoral head bearings (HR 1.02 [95% CI 0.76 to 1.37]; p = 0.89). At 5 years, the CPR of dual-mobility constructs was 17.6% for all aseptic-cause second revision (95% CI 12.6% to 24.3%) and 17.8% for large femoral head bearings (95% CI 14.9% to 21.2%). When stratified by acetabular component sizes less than 58 mm and at least 58 mm, there was no difference in the re-revision CPR for dislocation or for all aseptic causes between dual-mobility constructs and large femoral head bearings.

CONCLUSION

Either dual-mobility constructs or large femoral head bearings can be used in revision THA, regardless of acetabular component size, as they did not differ in terms of re-revision rates for dislocation and all aseptic causes in this registry study. Longer term follow-up is required to assess whether complications develop with either implant or whether a difference in revision rates becomes apparent. Ongoing follow-up and comparison in a registry format would seem the best way to compare long-term complications and revision rates. Future studies should also compare surgeon factors and whether they influence decision-making between prosthesis options and second revision rates. Nested randomized controlled trials in national registries would seem a viable option for future research.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Dual-mobility constructs versus large femoral head bearings in primary and revision total hip arthroplasty: a systematic review and meta-analysis of comparative studies

BACKGROUND

Both dual-mobility (DM) constructs and large femoral head bearings (⩾36 mm) reduce dislocation following total hip arthroplasty (THA). There is limited research comparing DM with large bearings.

METHODS

A systematic review of published literature was performed including studies that compared DM with large femoral head bearings in primary or revision THA according to PRISMA guidelines. The primary outcome was revision surgery for dislocation. The secondary outcome was all-cause revision surgery. Other complications were recorded. 2 authors independently selected studies, performed data extraction, and risk of bias assessment. Treatment effects were assessed using odds ratios and data were pooled using a fixed-effect model, where appropriate.

RESULTS

9 studies, all retrospective, met the final inclusion criteria. 2722 patients received DM and 9,789 large femoral head bearings. The difference in the odds of revision surgery for dislocation (OR 0.67; 95% CI, 0.45-1.01; p = 0.06) and aseptic loosening are unclear (OR 0.61; 95% CI, 0.36-1.05; p = 0.07); including important benefits and no difference. There was a benefit favouring DM for the risk of all-cause revision (OR 0.70; 95% CI, 0.56-0.86; p = 0.001), revision for fracture (OR 0.49; 95% CI, 0.29-0.81; p = 0.005) and dislocation not requiring revision (OR 0.29; 95% CI, 0.14-0.57; p < 0.001). The estimate in the difference in the odds of revision surgery for infection was imprecise (OR 0.78; 95% CI, 05.1-1.20; p = 0.26).

CONCLUSIONS

This study provides evidence that there may be clinically relevant benefits of DM constructs over large femoral head bearings. Prospective randomised studies are warranted given these findings.

Monobloc Dual Mobility With a Minimum 5-Year Follow-Up: A Safe and Effective Solution in Primary Total Hip Arthroplasty

BACKGROUND

Instability constitutes over 20% of revisions after total hip arthroplasty (THA). Dual mobility (DM) designs were introduced as a solution to this problem. However, the few publications that have reported promising results for monobloc DM constructs have been limited by sample size or length of follow-up. The purpose of this study is to evaluate mid-term outcomes (minimum 5-year follow-up) of a single-surgeon series utilizing a monobloc DM acetabular component in patients with high risk for dislocation.

METHODS

This is a single-surgeon consecutive series of 207 primary THAs implanted with a monobloc DM component in patients who were considered at high risk for dislocation. Patient demographics and case-specific data were collected retrospectively. All patients had a minimum of 5-year follow-up. The Mann-Whitney U test was used to assess continuous variables, whereas categorical variables were analyzed using the chi-square test. Survival probability was calculated using the Kaplan-Meier method.

RESULTS

Radiographic analysis did not reveal acetabular radiolucency in any patients, and there were no revisions for aseptic loosening. In addition, there were no dislocations. Seven of 205 patients (3.4%) were revised, 5 on the femoral side due to periprosthetic fracture and the remaining two for infection. Survivorship of the acetabular component from revision was 99%. The mean Veteran RAND (VR-12) physical score improved from 7 (standard deviation [SD]: 13.7) preoperatively to 9.5 (SD: 17.6) at the final follow-up. Similarly, the hip disability osteoarthritis score improved from 8 (SD: 17.9) preoperatively to 21.2 (SD: 37).

CONCLUSION

Monobloc DM components reliably prevent dislocation after primary THA in high-risk patients. At mid-term follow-up, this DM monobloc component demonstrates excellent implant survivorship, radiographic fixation, and improved functional outcomes.

Trends of Femoral Neck Fracture Treatment Using Total Hip Arthroplasty: Reported From the American Joint Replacement Registry

INTRODUCTION

Total hip arthroplasty (THA) rather than hemiarthroplasty for displaced femoral neck fracture (FNF) is often chosen for younger patients who are more active and/or have underlying hip osteoarthritis. However, instability remains the primary concern of doing THA. Dual mobility (DM) has been shown to decrease this risk through a larger effective head size and greater head-to-neck ratio compared with conventional THA. The purpose of this study was to identify femoral head size and DM usage patterns for the treatment of FNF with THA in the United States using the American Joint Replacement Registry.

METHODS

A retrospective cohort study was conducted, including all primary THAs done for FNF from 2012 to 2019. THA and FNF were defined using Current Procedural Terminology or International Classification of Diseases-9 or -10 diagnosis and procedure codes. Analysis was based on patient demographics, femoral head size, and DM usage. Descriptive statistics were used using a Pearson chi-square test. All analyses were conducted using SAS version 9.4, and statistical significance was set at P < 0.05.

RESULTS

There were 18,752 THAs done by 3,242 surgeons at 789 institutions during the 8-year study period. The overall population was 66% female, and the mean age was 72.3 ± 11.8 years. The most commonly used femoral head size was 36 mm (48.5%) followed by 32 mm (24.5%), ≤28 mm (10.7%), DM (10.8%), and ≥40 mm (5.7%). A trend was observed toward decreased use of ≤28, 32, and ≥40-mm heads starting in 2016 across the years and increased use of 36-mm heads (P < 0.0001). A significant increase was observed in the usage of DM over time from 6.4% in 2012 to 16.2% in 2019 (P < 0.0001).

DISCUSSION

Most of the femoral heads used were ≥36 mm, and the use of DM increased during the study period. Additional analysis is warranted to understand how these trends will affect overall outcomes and postoperative dislocation rates.

No Difference in Dislocation Rates Comparing Large Diameter Jumbo Femoral Heads and Dual-Mobility Bearings in Revision Total Hip Arthroplasty

BACKGROUND

Dual-mobility (DM) bearings reduce instability in revision total hip arthroplasty (THA); however, DM bearings are costly and reports of corrosion have recently emerged. Furthermore, no study has compared DM to standard bearings with large diameter femoral heads ≥40-mm. This study's purpose was to compare postoperative dislocation rates of standard and DM bearings with large femoral heads after revision THA.

METHODS

A retrospective review of 301 consecutive revision THAs was performed. The mean follow-up was 37.1 months. To isolate the effect of the double articulation, standard and DM bearings with femoral heads ≥40-mm were compared. Outcomes were postoperative dislocation and reoperation within 90 days.

RESULTS

The cohort consisted of 182 standard bearings and 75 DM bearings. There were no differences in revision indication comparing standard and DM bearings (P = .258). Overall dislocation rate was 8.6% (22 of 257). The dislocation rate was 5.7% for standard bearings with ≥40-mm femoral heads compared with 6.9% in DM bearings with ≥40-mm femoral heads (P = 1.000). In multivariate analysis, lower body mass index (odds ratio 1.72), female sex (odds ratio 2.01), and decreased outer femoral head diameter-to-cup component size ratio (odds ratio 1.64) were predictors of postoperative dislocation regardless of bearing type.

CONCLUSION

This study showed no difference in dislocation rates between standard and DM bearings when comparing similar femoral head diameters of ≥40-mm used in revision THAs. Considering the cost and potential deleterious issues associated with additional interfaces, DM bearings should be used judiciously considering similar results may be achieved with single-articulation bearings using large femoral heads.

LEVEL OF EVIDENCE

Level III.

A Comparison of Revision Rates for Dislocation and Aseptic Causes Between Dual Mobility and Large Femoral Head Bearings in Primary Total Hip Arthroplasty With Subanalysis by Acetabular Component Size: An Analysis of 106,163 Primary Total Hip Arthroplasties

BACKGROUND

Dual mobility (DM) and large femoral head bearings (≥36 mm) both decrease the risk of dislocation in total hip arthroplasty (THA). There is limited comparable data in primary THA. This study compared the revision rates for dislocation and aseptic causes between DM and large femoral heads and subanalyzed by acetabular component size.

METHODS

Data from the Australian Orthopedic Association National Joint Replacement Registry were analyzed for patients undergoing primary THA for osteoarthritis from January 2008 (the year of first recorded DM use) to December 2019. All DM and large femoral head bearings were identified. The primary outcome measure was the cumulative percent revision (CPR) for dislocation and for all aseptic causes. The results were adjusted by age, sex, and femoral fixation. A subanalysis was performed stratifying acetabular component diameter <58 m and ≥58 mm.

RESULTS

There were 4942 DM and 101,221 large femoral head bearings recorded. There was no difference in the CPR for dislocation (HR = 0.69 (95% CI 0.42, 1.13), P = .138) or aseptic causes (HR = 0.91 (95% CI 0.70, 1.18), P = .457). When stratified by acetabular component size, DM reduced the CPR for dislocation in acetabular component diameter <58 mm (HR = 0.55 (95% CI 0.30, 1.00), P = .049). There was no difference for diameter ≥58 mm. There was no difference in aseptic revision when stratified by acetabular component diameter.

CONCLUSION

There is no difference in revision rates for dislocation or aseptic causes between DM and large femoral heads in primary THA. When stratified by acetabular component size, DM reduces dislocation for acetabular component diameter <58 mm.

LEVEL OF EVIDENCE

Level III.

Femoral Neck Notching in Dual Mobility Implants: Is This a Reason for Concern?

BACKGROUND

Dual mobility (DM) total hip arthroplasty (THA) implants have been advocated for patients at risk for impingement due to abnormal spinopelvic mobility. Impingement against cobalt-chromium acetabular bearings, however, can result in notching of titanium femoral stems. This study investigated the incidence of femoral stem notching associated with DM implants and sought to identify risk factors.

METHODS

A multicenter retrospective study reviewed 256 modular and 32 monoblock DM components with minimum 1-year clinical and radiographic follow-up, including 112 revisions, 4 conversion THAs, and 172 primary THAs. Radiographs were inspected for evidence of femoral notching and to calculate acetabular inclination and anteversion. Revisions and dislocations were recorded.

RESULTS

Ten cases of femoral notching were discovered (3.5%), all associated with modular cylindrospheric cobalt-chromium DM implants (P = .049). Notches were first observed radiographically at mean 1.3 years after surgery (range 0.5-2.7 years). Notch location was anterior (20%), superior (60%), or posterior (20%) on the prosthetic femoral neck. Notch depth ranged from 1.7% to 20% of the prosthetic neck diameter. Eight cases with notching had lumbar pathology that can affect spinopelvic mobility. None of these notches resulted in stem fracture, at mean 2.7-year follow-up (range 1-7.6 years). There were no dislocations or revisions in patients with notching.

CONCLUSION

Femoral notching was identified in 3.5% of DM cases, slightly surpassing the dislocation rate in a cohort selected for risk of impingement and instability. Although these cases of notching have not resulted in catastrophic failures thus far, further study of clinical sequelae is warranted. Component position, spinopelvic mobility, and implant design may influence risk.

Modular dual mobility total hip arthroplasty is a viable option for young, active patients : a mid-term follow-up study

AIMS

Dual mobility (DM) implants have been shown to reduce the dislocation rate after total hip arthroplasty (THA), but there remain concerns about the use of cobalt chrome liners inserted into titanium shells. The aim of this study was to assess the clinical outcomes, metal ion levels, and periprosthetic femoral bone mineral density (BMD) at mid-term follow-up in young, active patients receiving a modular DM THA.

METHODS

This was a prospective study involving patients aged < 65 years, with a BMI of < 35 kg/m², and University of California, Los Angeles activity score of > 6 who underwent primary THA with a modular cobalt chrome acetabular liner, highly cross-linked polyethylene mobile bearing, and a cementless titanium femoral stem. Patient-reported outcome measures, whole blood metal ion levels (μg/l), and periprosthetic femoral BMD were measured at baseline and at one, two, and five years postoperatively. The results two years postoperatively for this cohort have been previously reported.

RESULTS

A total of 43 patients were enrolled. At minimum follow-up of five years, 23 (53.4%) returned for clinical and radiological review, 25 (58.1%) had metal ion analysis performed, 19 (44.2%) underwent dual energy x-ray absorptiometry scans, and 25 (58%) completed a pain-drawing questionnaire. The mean modified Harris Hip Scores improved significantly from 54.8 (SD 19) preoperatively to 93.08 (SD 10.5) five years postoperatively (p < 0.001). One patient was revised for aseptic acetabular loosening. The mean cobalt levels increased from 0.065 μg/l (SD 0.03) to 0.08 (SD 0.05) and the mean titanium levels increased from 0.35 (SD 0.13) to 0.78 (SD 0.29). The femoral BMD ratio decreased in Gruen Zone 1 (91.9%) at five years postoperatively compared with the baseline scores at six weeks potoperatively. The femoral BMD ratio was maintained in Gruen zones 2 to 7.

CONCLUSION

The use of a modular DM component and a cementless, tapered femoral stem shows excellent mid-term survivorship with minimal concerns for corrosion and metal ion release in a cohort of young, active patients undergoing primary THA. Cite this article: Bone Joint J 2021;103-B(7 Supple B):73-77.

Fretting Corrosion, Third-Body Polyethylene Damage, and Cup Positioning in Primary vs Revision Dual Mobility Total Hip Arthroplasty

BACKGROUND

Dual mobility (DM) articulations were introduced for total hip arthroplasty to reduce the risk of instability for patients who have a high risk of dislocation. The use of DM constructs in both primary and revision total hip arthroplasty has been steadily increasing, leading to concerns regarding potential risks of fretting corrosion, polyethylene wear, metal release, and failure due to component positioning.

METHODS

A total of 56 retrieved DM constructs were collected. The inner and outer polyethylene liner surfaces were assessed for 7 damage mechanisms, and fretting corrosion was evaluated for the femoral stem, head, and modular liner. Three polyethylene liners with the greatest amounts of embedded debris were examined using scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to determine the elemental content of the debris. Acetabular cup orientation was analyzed radiographically using the EBRA (Einzel-Bild-Roentgen-Analyse) method.

RESULTS

The devices were revised most frequently for infection (36%), loosening (21%), and instability/dislocation (18%). The most common polyethylene damage mechanisms were scratching, pitting, burnishing, and embedded debris, and no difference in total damage was found between primary and revision cases. Scanning electron microscopy/energy-dispersive X-ray spectroscopy revealed that debris morphology and composition were consistent with porous titanium coating, resulting from cup loosening or broken screws and augments. A total of 71% and 50% of the constructs were determined to be within the Lewinnek safe zone for inclination and anteversion, respectively.

CONCLUSION

The most notable mechanisms of surface damage were due to third-body debris, especially for the polyethylene surfaces which articulate against cobalt-chromium femoral heads and acetabular liners. Scratching of the femoral head and the metal liner from this debris may support the clinical use of ceramic for DM bearing surfaces in the future.