Aims. The aim of this study was to investigate whether wear and backside deformation of polyethylene (PE) tibial inserts may influence the cement cover of tibial trays of explanted total knee arthroplasties (TKAs). Methods. At our retrieval centre, we measured changes in the wear and deformation of PE inserts using coordinate measuring machines and light microscopy. The amount of cement cover on the backside of tibial trays was quantified as a percentage of the total surface. The study involved data from the explanted fixed-bearing components of four widely used contemporary designs of TKA (Attune, NexGen, Press Fit Condylar (PFC), and Triathlon), revised for any indication, and we compared them with components that used previous generations of PE. Regression modelling was used to identify variables related to the amount of cement cover on the retrieved trays. Results. A total of 114 explanted fixed-bearing TKAs were examined. This included 76 used with contemporary PE inserts which were compared with 15 used with older generation PEs. The Attune and NexGen (central locking) trays were found to have significantly less cement cover than Triathlon and PFC trays (peripheral locking group) (p = 0.001). The median planicity values of the PE inserts used with central locking trays were significantly greater than of those with peripheral locking inserts (205 vs 85 microns; p < 0.001). Attune and NexGen inserts had a characteristic pattern of backside deformation, with the outer edges of the PE deviating inferiorly, leaving the PE margins as the primary areas of articulation. Conclusion. Explanted TKAs with central locking mechanisms were significantly more likely to debond from the cement mantle. The PE inserts of these designs showed characteristic patterns of deformation, which appeared to relate to the manufacturing process and may be exacerbated in vivo. This pattern of deformation was associated with PE wear occurring at the outer edges of the articulation, potentially increasing the frictional torque generated at this interface. Cite this article: Bone Joint J 2021;103-B(12):1791–1801

Aims

This study investigates head-neck taper corrosion with varying head size in a novel hip simulator instrumented to measure corrosion related electrical activity under torsional loads.

Aims

Acetabular edge-loading was a cause of increased wear rates in metal-on-metal hip arthroplasties, ultimately contributing to their failure. Although such wear patterns have been regularly reported in retrieval analyses, this study aimed to determine their in vivo location and investigate their relationship with acetabular component positioning.

Aims

The optimum clearance between the bearing surfaces of hip arthroplasties is unknown. Theoretically, to minimize wear, it is understood that clearances must be low enough to maintain optimal contact pressure and fluid film lubrication, while being large enough to allow lubricant recovery and reduce contact patch size. This study aimed to identify the relationship between diametrical clearance and volumetric wear, through the analysis of retrieved components.

Aims. A retrospective longitudinal study was conducted to compare directly volumetric wear of retrieved polyethylene inserts to predicted volumetric wear modelled from individual gait mechanics of total knee arthroplasty (TKA) patients. Methods. In total, 11 retrieved polyethylene tibial inserts were matched with gait analysis testing performed on those patients. Volumetric wear on the articular surfaces was measured using a laser coordinate measure machine and autonomous reconstruction. Knee kinematics and kinetics from individual gait trials drove computational models to calculate medial and lateral tibiofemoral contact paths and forces. Sliding distance along the contact path, normal forces and implantation time were used as inputs to Archard’s equation of wear to predict volumetric wear from gait mechanics. Measured and modelled wear were compared for each component. Results. Volumetric wear rates on eight non-delaminated components measured 15.9 mm. 3. /year (standard error (SE) ± 7.7) on the total part, 11.4 mm. 3. /year (SE ± 6.4) on the medial side and 4.4 (SE ± 2.6) mm. 3. /year on the lateral side. Volumetric wear rates modelled from patient gait mechanics predicted 16.4 mm. 3. /year (SE 2.4) on the total part, 11.7 mm. 3. /year (SE 2.1) on the medial side and 4.7 mm. 3. /year (SE 0.4) on the lateral side. Measured and modelled wear volumes correlated significantly on the total part (p = 0.017) and the medial side (p = 0.012) but not on the lateral side (p = 0.154). Conclusion. In the absence of delamination, patient-specific knee mechanics during gait directly affect wear of the tibial component in TKA. Cite this article: Bone Joint J 2020;102-B(6 Supple A):129–137

Objectives

We investigated the reliability of the cobalt-chromium (CoCr) synovial joint fluid ratio (JFR) in identifying the presence of a severe aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) response and/or suboptimal taper performance (SOTP) following metal-on-metal (MoM) hip arthroplasty. We then examined the possibility that the CoCr JFR may influence the serum partitioning of Co and Cr.

Objectives

Previous studies have suggested that metal-on-metal (MoM) Pinnacle (DePuy Synthes, Warsaw, Indiana) hip arthroplasties implanted after 2006 exhibit higher failure rates. This was attributed to the production of implants with reduced diametrical clearances between their bearing surfaces, which, it was speculated, were outside manufacturing tolerances. This study aimed to better understand the performance of Pinnacle Systems manufactured before and after this event.

Objectives

We have encountered patients who developed large joint fluid collections with massive elevations in chromium (Cr) and cobalt (Co) concentrations following metal-on-metal (MoM) hip arthroplasties. In some cases, retrieval analysis determined that these ion concentrations could not be explained simply by the wear rates of the components. We hypothesized that these effects may be associated with aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL).

Aims. We sought to determine whether cobalt-chromium alloy (CoCr) femoral stem tapers (trunnions) wear more than titanium (Ti) alloy stem tapers (trunnions) when used in a large diameter (LD) metal-on-metal (MoM) hip arthroplasty system. Patients and Methods. We performed explant analysis using validated methodology to determine the volumetric material loss at the taper surfaces of explanted LD CoCr MoM hip arthroplasties used with either a Ti alloy (n = 28) or CoCr femoral stem (n = 21). Only 12/14 taper constructs with a rough male taper surface and a nominal included angle close to 5.666° were included. Multiple regression modelling was undertaken using taper angle, taper roughness, bearing diameter (horizontal lever arm) as independent variables. Material loss was mapped using a coordinate measuring machine, profilometry and scanning electron microscopy. Results. After adjustment for other factors, CoCr stem tapers were found to have significantly greater volumetric material loss than the equivalent Ti stem tapers. Conclusion. When taper junction damage is identified during revision of a LD MoM hip, it should be suspected that a male taper composed of a standard CoCr alloy has sustained significant changes to the taper cone geometry which are likely to be more extensive than those affecting a Ti alloy stem. Cite this article: Bone Joint J 2017;99-B:1304–12

Objectives. The high revision rates of the DePuy Articular Surface Replacement (ASR) and the DePuy ASR XL (the total hip arthroplasty (THA) version) have led to questions over the viability of metal-on-metal (MoM) hip joints. Some designs of MoM hip joint do, however, have reasonable mid-term performance when implanted in appropriate patients. Investigations into the reasons for implant failure are important to offer help with the choice of implants and direction for future implant designs. One way to assess the performance of explanted hip prostheses is to measure the wear (in terms of material loss) on the joint surfaces. Methods. In this study, a coordinate measuring machine (CMM) was used to measure the wear on five failed cementless Biomet Magnum/ReCap/ Taperloc large head MoM THAs, along with one Biomet ReCap resurfacing joint. Surface roughness measurements were also taken. The reason for revision of these implants was pain and/or adverse reaction to metal debris (ARMD) and/or elevated blood metal ion levels. Results. The mean wear rate of the articulating surfaces of the heads and acetabular components of all six joints tested was found to be 6.1 mm. 3. /year (4.1 to 7.6). The mean wear rate of the femoral head tapers of the five THAs was 0.054 mm. 3. /year (0.021 to 0.128) with a mean maximum wear depth of 5.7 µm (4.3 to 8.5). Conclusion. Although the taper wear was relatively low, the wear from the articulating surfaces was sufficient to provide concern and was potentially large enough to have been the cause of failure of these joints. The authors believe that patients implanted with the ReCap system, whether the resurfacing prosthesis or the THA, should be closely monitored. Cite this article: S. C. Scholes, B. J. Hunt, V. M. Richardson, D. J. Langton, E. Smith, T. J. Joyce. Explant analysis of the Biomet Magnum/ReCap metal-on-metal hip joint. Bone Joint Res 2017;6:113–122. DOI: 10.1302/2046-3758.62.BJR-2016-0130.R2

Aims

Surgeons have commonly used modular femoral heads and stems from different manufacturers, although this is not recommended by orthopaedic companies due to the different manufacturing processes.

We compared the rate of corrosion and rate of wear at the trunnion/head taper junction in two groups of retrieved hips; those with mixed manufacturers (MM) and those from the same manufacturer (SM).

Objectives

Wear debris released from bearing surfaces has been shown to provoke negative immune responses in the recipient. Excessive wear has been linked to early failure of prostheses. Analysis using coordinate measuring machines (CMMs) can provide estimates of total volumetric material loss of explanted prostheses and can help to understand device failure. The accuracy of volumetric testing has been debated, with some investigators stating that only protocols involving hundreds of thousands of measurement points are sufficient. We looked to examine this assumption and to apply the findings to the clinical arena.

A modular femoral head–neck junction has practical advantages in total hip replacement. Taper fretting and corrosion have so far been an infrequent cause of revision. The role of design and manufacturing variables continues to be debated. Over the past decade several changes in technology and clinical practice might result in an increase in clinically significant taper fretting and corrosion. Those factors include an increased usage of large diameter (36 mm) heads, reduced femoral neck and taper dimensions, greater variability in taper assembly with smaller incision surgery, and higher taper stresses due to increased patient weight and/or physical activity. Additional studies are needed to determine the role of taper assembly compared with design, manufacturing and other implant variables.

Cite this article: Bone Joint J 2013;95-B, Supple A:3–6.

Objectives. The aims of this piece of work were to: 1) record the background concentrations of blood chromium (Cr) and cobalt (Co) concentrations in a large group of subjects; 2) to compare blood/serum Cr and Co concentrations with retrieved metal-on-metal (MoM) hip resurfacings; 3) to examine the distribution of Co and Cr in the serum and whole blood of patients with MoM hip arthroplasties; and 4) to further understand the partitioning of metal ions between the serum and whole blood fractions. Methods. A total of 3042 blood samples donated to the local transfusion centre were analysed to record Co and Cr concentrations. Also, 91 hip resurfacing devices from patients who had given pre-revision blood/serum samples for metal ion analysis underwent volumetric wear assessment using a coordinate measuring machine. Linear regression analysis was carried out and receiver operating characteristic curves were constructed to assess the reliability of metal ions to identify abnormally wearing implants. The relationship between serum and whole blood concentrations of Cr and Co in 1048 patients was analysed using Bland-Altman charts. This relationship was further investigated in an in vitro study during which human blood was spiked with trivalent and hexavalent Cr, the serum then separated and the fractions analysed. Results. Only one patient in the transfusion group was found to have a blood Co > 2 µg/l. Blood/Serum Cr and Co concentrations were reliable indicators of abnormal wear. Blood Co appeared to be the most useful clinical test, with a concentration of 4.5 µg/l showing sensitivity and specificity for the detection of abnormal wear of 94% and 95%, respectively. Generated metal ions tended to fill the serum compartment preferentially in vivo and this was replicated in the in vitro study when blood was spiked with trivalent Cr and bivalent Co. Conclusions. Blood/serum metal ion concentrations are reliable indicators of abnormal wear processes. Important differences exist however between elements and the blood fraction under study. Future guidelines must take these differences into account

Radiological assessment of total and unicompartmental knee replacement remains an essential part of routine care and follow-up. Appreciation of the various measurements that can be identified radiologically is important. It is likely that routine plain radiographs will continue to be used, although there has been a trend towards using newer technologies such as CT, especially in a failing knee, where it provides more detailed information, albeit with a higher radiation exposure.

The purpose of this paper is to outline the radiological parameters used to evaluate knee replacements, describe how these are measured or classified, and review the current literature to determine their efficacy where possible.

Objectives

An ongoing prospective study to investigate failing metal-on-metal hip prostheses was commenced at our centre in 2008. We report on the results of the analysis of the first consecutive 126 failed mated total hip prostheses from a single manufacturer.

Alumina–alumina bearings are among the most resistant to wear in total hip replacement. Examination of their surfaces is one way of comparing damage caused by wear of hip joints simulated in vitro to that seen in explanted bearings. The aim of this study was to determine whether second-generation ceramic bearings exhibited a better pattern of wear than those reported in the literature for first-generation bearings. We considered both macro- and microscopic findings.

We found that long-term alumina wear in association with a loose acetabular component could be categorised into three groups. Of 20 specimens, four had ‘low wear’, eight ‘crescent wear’ and eight ‘severe wear’, which was characterised by a change in the physical shape of the bearing and a loss of volume. This suggests that the wear in alumina–alumina bearings in association with a loose acetabular component may be variable in pattern, and may explain, in part, why the wear of a ceramic head in vivo may be greater than that seen after in vitro testing.

There is widespread concern regarding the incidence of adverse soft-tissue reactions after metal-on-metal (MoM) hip replacement. Recent National Joint Registry data have shown clear differences in the rates of failure of different designs of hip resurfacing. Our aim was to update the failure rates related to metal debris for the Articular Surface Replacement (ASR). A total of 505 of these were implanted.

Kaplan-Meier analysis showed a failure rate of 25% at six years for the ASR resurfacing and of 48.8% for the ASR total hip replacement (THR). Of 257 patients with a minimum follow-up of two years, 67 (26.1%) had a serum cobalt concentration which was greater than 7 μg/l. Co-ordinate measuring machine analysis of revised components showed that all patients suffering adverse tissue reactions in the resurfacing group had abnormal wear of the bearing surfaces. Six THR patients had relatively low rates of articular wear, but were found to have considerable damage at the trunion-taper interface. Our results suggest that wear at the modular junction is an important factor in the development of adverse tissue reactions after implantation of a large-diameter MoM THR.

This study reports the mid-term results of a large-bearing hybrid metal-on-metal total hip replacement in 199 hips (185 patients) with a mean follow-up of 62 months (32 to 83).

Two patients died of unrelated causes and 13 were lost to follow-up. In all, 17 hips (8.5%) have undergone revision, and a further 14 are awaiting surgery. All revisions were symptomatic. Of the revision cases, 14 hips showed evidence of adverse reactions to metal debris. The patients revised or awaiting revision had significantly higher whole blood cobalt ion levels (p = 0.001), but no significant difference in acetabular component size or position compared with the unrevised patients. Wear analysis (n = 5) showed increased wear at the trunnion-head interface, normal levels of wear at the articulating surfaces and evidence of corrosion on the surface of the stem.

The cumulative survival rate, with revision for any reason, was 92.4% (95% confidence interval 87.4 to 95.4) at five years. Including those awaiting surgery, the revision rate would be 15.1% with a cumulative survival at five years of 89.6% (95% confidence interval 83.9 to 93.4).

This hybrid metal-on-metal total hip replacement series has shown an unacceptably high rate of failure, with evidence of high wear at the trunnion-head interface and passive corrosion of the stem surface. This raises concerns about the use of large heads on conventional 12/14 tapers.

Hip simulators have been used for ten years to determine the tribological performance of large-head metal-on-metal devices using traditional test conditions. However, the hip simulator protocols were originally developed to test metal-on-polyethylene devices. We have used patient activity data to develop a more physiologically relevant test protocol for metal-on-metal devices. This includes stop/start motion, a more appropriate walking frequency, and alternating kinetic and kinematic profiles.

There has been considerable discussion about the effect of heat treatments on the wear of metal-on-metal cobalt chromium molybdenum (CoCrMo) devices. Clinical studies have shown a higher rate of wear, levels of metal ions and rates of failure for the heat-treated metal compared to the as-cast metal CoCrMo devices. However, hip simulator studies in vitro under traditional testing conditions have thus far not been able to demonstrate a difference between the wear performance of these implants.

Using a physiologically relevant test protocol, we have shown that heat treatment of metal-on-metal CoCrMo devices adversely affects their wear performance and generates significantly higher wear rates and levels of metal ions than in as-cast metal implants.

Two Durasul highly crosslinked polyethylene liners were exchanged during revision surgery four and five years after implantation, respectively. The retrieved liners were evaluated macroscopically and surface analysis was performed using optical and electron microscopy. A sample of each liner was used to determine the oxidation of the material by Fourier transform infrared spectroscopy. Samples of the capsule were examined histologically.

The annual wear rate was found to be 0.010 and 0.015 mm/year, respectively. Surface analysis showed very little loss of material caused by wear. Histological evaluation revealed a continuous neosynovial lining with single multinucleated foreign-body giant cells. Our findings showed no unexpected patterns of wear on the articulating surfaces up to five years after implantation and no obvious failure of material.

There are many methods for analysing wear volume in failed polyethylene acetabular components. We compared a radiological technique with three recognised ex vivo methods of measurement.

We tested 18 ultra-high-molecular-weight polyethylene acetabular components revised for wear and aseptic loosening, of which 13 had pre-revision radiographs, from which the wear volume was calculated based upon the linear wear. We used a shadowgraph technique on silicone casts of all of the retrievals and a coordinate measuring method on the components directly. For these techniques, the wear vector was calculated for each component and the wear volume extrapolated using mathematical equations. The volumetric wear was also measured directly using a fluid-displacement method. The results of each technique were compared.

The series had high wear volumes (mean 1385 mm³; 730 to 1850) and high wear rates (mean 205 mm³/year; 92 to 363). There were wide variations in the measurements of wear volume between the radiological and the other techniques. Radiograph-derived wear volume correlated poorly with that of the fluid-displacement method, co-ordinate measuring method and shadowgraph methods, becoming less accurate as the wear increased. The mean overestimation in radiological wear volume was 47.7% of the fluid-displacement method wear volume.

Fluid-displacement method, coordinate measuring method and shadowgraph determinations of wear volume were all better than that of the radiograph-derived linear measurements since they took into account the direction of wear. However, only radiological techniques can be used in vivo and remain useful for monitoring linear wear in the clinical setting.

Interpretation of radiological measurements of acetabular wear must be done judiciously in the clinical setting. In vitro laboratory techniques, in particular the fluid-displacement method, remain the most accurate and reliable methods of assessing the wear of acetabular polyethylene.