A Retrieval Analysis of Impingement in Dual-Mobility Liners

Impingement testing of total hip replacements according to ASTM F2582 - Implant wear, resistance to damage and acceptance criteria

OBJECTIVES

The aim of this study was to determine the resistance to impingement damage of three different artificially aged UHMWPE materials used for total hip joint replacement. The results obtained can be used as a basis for an acceptance criterion for testing according to ASTM F2582-20.

METHODS

Three different polyethylene liner materials, standard polyethylene (UHMWPE), moderately crosslinked (XLPE) and vitamin E stabilized crosslinked (XLPE-VE) polyethylene of the same design and manufacturer were tested up to one million impingement cycles according to ASTM F2582-20. The liners were artificially oxygen aged for two and three weeks according to ASTM F2003-02. The wear volumes of the liner, acetabular shells, and hip endoprosthesis stems were determined. Each of the six impingement test groups consisted of three samples. For each test group, a reference group was subjected to the same conditioning and loading conditions but without impingement between the hip stem and the liner. The force needed to disassemble the liner from the acetabular shell (push-out force) was determined according to ASTM F1820-22 for the test and the reference groups.

RESULTS

XLPE and XLPE-VE polyethylene groups showed less impingement wear when compared to the standard UHMWPE material. Similarly, the protective function of the liner against direct metal-on-metal contact was greater, resulting in less wear on the acetabular shell and the stem neck. The three weeks aged standard UHMWPE group showed early onset of fatigue delamination wear. The push-out values remained unchanged for all XLPE liners and the 3-week aged XLPE-VE liners. The aged UHMWPE liners showed low push-out strength due to component shrinkage caused by aging in combination with the tapered fixation used for this specific design.

SIGNIFICANCE

The largest polyethylene wear volume measured of XLPE and XLPE-VE polyethylene aged for two and three weeks was 15.05 mm³ (SD 0.56 mm³). The corresponding metal wear volume was 1.23 mm³ (SD 0.19 mm³) for the acetabular cup and 1.33 mm³ (SD 0.20 mm³) for the stem neck. Those values can support the definition of an acceptance criteria for impingement testing. The results of the push-out test required by ASTM F2582-20 should be evaluated with respect to geometry changes caused by aging. The protective effect of the polyethylene liner against metal-on-metal contact should be considered in the implant design phase in order to avoid implant failure due to metal debris.

Femoral Neck Design Does Not Impact Revision Risk After Primary Total Hip Arthroplasty Using a Dual Mobility Cup

Background

The use of dual mobility (DM) cups has increased quickly. It is hypothesized that femoral neck taper geometry may be involved in the risk of prosthetic impingement and DM cup revision. We aim to (1) explore the reasons for revision of DM cups or head/liners and (2) explore whether certain femoral neck characteristics are associated with a higher risk of revision of DM cups.

Methods

Primary total hip arthroplasties with a DM cup registered in the Dutch Arthroplasty Register between 2007 and 2021 were identified (n = 7603). Competing risk survival analyses were performed, with acetabular component and head/liner revision as the primary endpoint. Reasons for revision were categorized in cup-/liner-related revisions (dislocation, liner wear, acetabular loosening). Femoral neck characteristics were studied to assess whether there is an association between femoral neck design and the risk of DM cup/liner revision. Multivariable Cox proportional hazard analyses were performed.

Results

The 5- and 10-year crude cumulative incidence of DM cup or head/liner revision for dislocation, wear, and acetabular loosening was 0.5% (CI 0.4-0.8) and 1.9% (CI 1.3-2.8), respectively. After adjusting for confounders, we found no association between the examined femoral neck characteristics (alloy used, neck geometry, CCD angle, and surface roughness) and the risk for revision for dislocation, wear, and acetabular loosening.

Conclusions

The risk of DM cup or head/liner revision for dislocation, wear, and acetabular loosening was low. We found no evidence that there is an association between femoral neck design and the risk of cup or head/liner revision.

Two-Year Outcomes of Novel Dual-Mobility Implant in Primary Total Hip Arthroplasty

Introduction

Dual-mobility (DM) implants for total hip arthroplasty (THA) have gained popularity due to their potential to reduce hip instability and dislocation events that may lead to revision surgery. These implants consist of a femoral head articulated within a polyethylene liner, which articulates within an outer acetabular shell, creating a dual-bearing surface. Our study aimed to report our observations on the survivorship of a novel DM implant for primary total hip arthroplasty at two years.

Methods

We conducted a retrospective, multicenter study to assess the clinical outcomes of patients undergoing a THA with a novel DM implant (OR3O acetabular system™, Smith & Nephew, Inc., Memphis, TN) from January 2020 to September 2021. Patient demographics, surgical information, and survivorship data were collected from medical records for patients with a minimum of two years of follow-up. Primary outcomes included overall implant survivorship at two years as well as aseptic survivorship, revision rates of the DM acetabular shell, and average time to revision. Patient-reported outcomes were collected in the form of HOOS JR.

Results

A total of 250 hips in 245 patients had a minimum two-year follow-up. Primary osteoarthritis (80%) was the most common indication for index THA. The average aseptic survivorship of the DM acetabular components at two years for the cohort was 98.4% and survivorship of the acetabular implants overall was 97.6%. There were a total of four (1.6%) aseptic revisions of the DM acetabular component. Reasons for aseptic acetabular revision included one case of instability, one intraprosthetic dislocation, one periprosthetic acetabular fracture, and one malpositioned acetabular cup resulting in impingement. The mean time of follow-up was 893.9 days. Eighty-seven patients had preoperative and two-year HOOS JR available. HOOS JR improved by an average of 38.5 points.

Conclusion

This novel DM acetabular implant demonstrates excellent survivorship at two years follow-up with low rates of instability and intraprosthetic dislocation and no episodes of metal-on-metal corrosion. Use of the DM implant demonstrated clinically relevant improvements in patient-reported outcomes at two years.

Combined kinematic cup alignment reduces the rate of impingement and edge loading compared to mechanical and anatomical alignment. An in-vitro case-control study

INTRODUCTION

In recent years, different alignments have been described for acetabular components in total hip arthroplasty (THA), to reduce the risk of impingement and edge loading. Currently there are 3 main options: mechanical (40° inclination/15° anteversion relative to the anterior pelvic plane), anatomic (40° inclination/anteversion parallel to the transverse ligament) and combined kinematic (according to spinal-pelvic parameters). There are no studies comparing all three in terms of impingement and edge loading. We therefore performed a retrospective case-control in-vitro study comparing risk of impingement and edge loading between the three alignments.

HYPOTHESIS

The study hypothesis was that combined kinematic alignment incurs significantly less risk of impingement and edge loading than do the other two types of alignment.

METHODS

Using a THA planning system, we simulated the 3 alignments for 90 patients undergoing THA with a ceramic-on-ceramic bearing between November 2019 and January 2022; for each simulation, we recorded any prosthetic impingement or edge loading. The study endpoint was the rate of prosthetic impingement or edge loading between the 3 alignments.

RESULTS

With the mechanical alignment, 31% of patients (28/90) showed risk of impingement and 22% (20/90) risk of edge loading. With the anatomic alignment, 31% of patients (28/90) showed risk of impingement and 23.3% (21/90) risk of edge loading. With the combined kinematic alignment, 12.2% of patients (11/90) showed risk of impingement and 8.9% (8/90) risk of edge loading. Pairwise comparison showed that the combined kinematic alignment was associated with significantly less impingement and edge loading than the mechanical alignment (respectively, p=0.03 and p=0.022) or the anatomic alignment (respectively, p=0.03 and p=0.014), while the mechanical and anatomic alignments did not differ.

CONCLUSION

A combined kinematic cup alignment in THA significantly reduced the risk of impingement and edge loading compared to mechanical and anatomic alignments.

LEVEL OF EVIDENCE

III, retrospective case-control study.

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.

Which femoral neck for a dual mobility cup? A biomechanical evaluation

Purpose

This study aimed to evaluate polyethylene (PE) damage and wear lesions to the chamfer of mobile components under mobile and fixed femoral neck impingement at the third articulation, and to determine which femoral neck characteristics should be considered with a dual mobility cup to limit those lesions.

Methods

Two femoral neck geometries (cylindrical and quadrangular) with two surface finishing roughness (rough and polished), and two head-to-neck ratios (28- and 22.2-mm diameter femoral heads) were evaluated in a hip simulator testing. For each characteristic, six femoral necks were tested with six dual mobility cups under fixed and mobile femoral neck impingement conditions. Chamfer PE damage and volumetric wear were evaluated and compared for each femoral neck characteristic and impingement condition.

Results

Under mobile impingement condition, femoral neck characteristics did not significantly affect PE damage and wear lesions to the chamfer (p = 0.283 to 0.810). However, under fixed impingement condition, significantly higher PE damage and wear lesions to the chamfer were produced by the quadrangular geometry compared to the cylindrical geometry (p = 0.004 to 0.025). In addition, with the quadrangular geometry, rough surface finishing was demonstrated to increase volumetric wear of the chamfer (p = 0.009). No significant influence of head-to-neck ratio was observed on PE damage and wear lesions to the chamfer (p = 0.244 to 0.714).

Discussion

This biomechanical study emphasized that femoral neck characteristics are critical with dual mobility cup and tend to favor a cylindrical geometry particularly whether fixed impingement at the third articulation occurs.

A novel hip joint prosthesis with uni-directional articulations for reduced wear

A novel polymer-on-metal hip joint prosthesis design that makes use of uni-directional articulations was developed and tested in this work. The new implant was tested using two polymer variants, virgin ultra-high molecular weight polyethylene (UHMWPE), and Vitamin E-infused highly crosslinked polyethylene (VEHXPE). The degrees of freedom of the ball-and-socket are reproduced by three cylindrical orthogonally-aligned articulations. This unconventional design leverages on the molecular orientation hardening mechanisms of the polyethylene and increased contact area to minimize wear. An experimental hip joint simulator was used to compare the gravimetric wear of the conventional ball-on-socket and the new implant. The new prosthesis including UHMWPE components produced a 78% reduction in wear, whereas the new prosthesis with VEHXPE components produced a 100% reduction in wear, as no measurable wear was detected. Machining marks on the acetabular cups of the new prosthesis were retained for both polyethylene variants, further demonstrating the low levels of wear exhibited by the new implants. Both polyethylene materials produced particles in the range of 0.1-1.0 μm, which are the most biologically active. Nonetheless, the extremely low wear rates are likely to induce minimal osteolysis effects. Furthermore, the novel design also offers an increase of more than 24% in the range of motion in flexion/extension when compared to a dual-mobility hip implant. A prototype of the prosthesis was implanted into a Thiel-embalmed human cadaver during a mock-surgery, which demonstrated high resistance to dislocation and the possibility of performing a figure of four position.

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.

Instability After Total Hip Arthroplasty and the Role of Advanced and Robotic Technology

Instability remains the leading cause of reoperation following total hip arthroplasty (THA). In this article, the risk factors for instability after THA are reviewed, including patient-related characteristics, surgical techniques, positioning of implants, and the role of advanced technology and robotics as a platform that may reduce the incidence of instability.

Migration and Wear of a Dual Mobility Acetabular Construct at 3 Years Measured by Radiostereometric Analysis

BACKGROUND

The anatomic dual mobility (ADM) acetabular component was introduced because of previously described low dislocation rates for this type of construct. The shape of the anatomic cup and the motion of polyethylene liner may have implications for acetabular cup fixation and polyethylene liner wear; therefore, the purpose of this study was to assess the migration patterns and wear rates of the ADM component using radiostereometric analysis.

METHODS

Uncemented ADM acetabular components were implanted in 27 patients. Radiostereometric analysis exams were taken at 6 follow-up visits over 3 years. Proximal translation and sagittal rotation of the cup and polyethylene total wear and wear rates were calculated. Oxford 12 Hip scores and satisfaction were recorded.

RESULTS

Mean proximal translation was below the 0.2 mm threshold at 2 years associated with acceptable long-term survivorship (0.16 mm [standard deviation {SD} 0.31] at 3 years). Mean sagittal rotation was 0.29 degrees (SD 1.03) and was greater in female subjects (P < .001). Following bedding-in, the annual wear rate was 0.02 mm/y, below the 0.1 mm/y threshold. There was no association between cup migration and polyethylene wear. Patient satisfaction at 3 years was 96%. Mean Oxford 12 Hip scores improved from 21 (SD 7) preoperatively to 43 (SD 7) 3 years postoperatively.

CONCLUSIONS

The ADM cup demonstrated stable migration at 3 years indicating low risk for aseptic loosening. Bedding-in in the first year was followed by low annual wear rates. These finding suggest no increased risk of the dual mobility and anatomic design on fixation or wear.

Is Isolated Mobile Component Exchange an Option in the Management of Intraprosthetic Dislocation of a Dual Mobility Cup?

BACKGROUND

Intraprosthetic dislocation is a specific complication of dual mobility cups, although it occurs less frequently with the latest generations of implants. Intraprosthetic dislocation is related to long-term polyethylene wear of the mobile component chamfer and retentive area, leading to a snap-out of the femoral head. With the increased use of dual mobility cups, even in younger and active patients, the management of intraprosthetic dislocation should be defined according to its type. However, no previous studies, except for case reports, have described the strategy to manage long-term wear-related intraprosthetic dislocation, particularly when a dual mobility cup is not loose.

QUESTIONS/PURPOSES

This study aimed to (1) determine the prevalence of intraprosthetic dislocation in this patient population and the macroscopic findings at the time of surgical revision and (2) evaluate whether isolated mobile component exchange could be an option to manage intraprosthetic dislocation occurring with a well-fixed dual mobility cup metal shell.

METHODS

From January 1991 to December 2009, a continuous series of 5274 THAs with dual mobility cups (4546 patients; 2773 women; mean [range] age 58 years [22-87]; bilateral THA = 728) were prospectively enrolled in our institutional total joint registry. A cementless, hemispherical dual mobility cup was systematically implanted, regardless of the patient's age or indication for THA. At the latest follow-up examination, the registry was queried to isolate each occurrence of intraprosthetic dislocation, which was retrospectively analyzed regarding the patient's demographics, indication for THA, radiographs, intraoperative findings (polyethylene wear and lesion patterns on the mobile component, periarticular metallosis, and implant damage because of intraprosthetic impingement of the femoral neck), management of intraprosthetic dislocation (isolated exchange of the mobile component or revision of the dual mobility cup), and outcome.

RESULTS

At a mean (range) follow-up duration of 14 years (3-26), 3% of intraprosthetic dislocations (169 of 5274) were reported, with a mean (range) time from THA of 18 years (13-22). Intraprosthetic dislocation occurred predominantly in younger men (mean [range] age at THA, 42 years [22-64] versus 61 years [46-87]; p < 0.001, and sex ratio (male to female, 1:32 [96 male and 73 female] versus 0.62 [1677 male and 2700 female]; p < 0.001) in patients with intraprosthetic dislocation and those without, respectively, but was not influenced by the indication for THA (105 patients with intraprosthetic dislocation who underwent THA for primary hip osteoarthritis and 64 with other diagnoses versus 3146 patients without who underwent THA for primary hip osteoarthritis and 1959 for other diagnoses (p = 0.9)). In all patients with intraprosthetic dislocation, a macroscopic analysis of the explanted mobile component revealed circumferential polyethylene wear and damage to the chamfer and retentive area, with subsequent loss of retaining power for the femoral head. Nine percent of intraprosthetic dislocations (16 of 169 patients with intraprosthetic dislocations) were associated with aseptic loosening of the dual mobility cup and were managed with acetabular revision without recurrence at a mean (range) follow-up duration of 7.5 years (5-11). Ninety-one percent of intraprosthetic dislocations (153 of 169) were pure, related to wear of the mobile component chamfer and retentive area without aseptic loosening of the dual mobility cup, and managed with isolated mobile component exchange. Intraprosthetic dislocation recurred in 6% (nine of 153) at a mean (range) follow-up interval of 3 years (2-4.5). Additionally, severe premature polyethylene wear of the mobile component with loosening of the dual mobility cup occurred in 12% of patients (19 of 153) at a mean (range) follow-up duration of 1.5 years (0.5-3).

CONCLUSIONS

A failure rate of 18% (28 of 153 patients undergoing isolated mobile component exchange) was reported within 5 years after isolated mobile component exchange to manage intraprosthetic dislocation occurring with a well-fixed dual mobility cup metal shell. The two modes of failure were early recurrence of intraprosthetic dislocation or severe premature metallosis-related polyethylene wear of the mobile component with loosening of the dual mobility cup. Acetabular revision with synovectomy should remain the standard procedure to manage intraprosthetic dislocation, particularly if periarticular metallosis is present. The exception is intraprosthetic dislocation occurring in elderly or frail patients, for whom a conventional acetabular revision procedure would be associated with an unjustified surgical or anesthetic risk.

LEVEL OF EVIDENCE

Level II, prognostic study.