Harinderjit Gill

Pseudotumours associated with metal-on-metal hip resurfacings

We report 17 patients (20 hips) in whom metal-on-metal resurfacing had been performed and who presented with various symptoms and a soft-tissue mass which we termed a pseudotumour. Each patient underwent plain radiography and in some, CT, MRI and ultrasonography were also performed. In addition, histological examination of available samples was undertaken. All the patients were women and their presentation was variable. The most common symptom was discomfort in the region of the hip. Other symptoms included spontaneous dislocation, nerve palsy, a noticeable mass or a rash. The common histological features were extensive necrosis and lymphocytic infiltration. To date, 13 of the 20 hips have required revision to a conventional hip replacement. Two are awaiting revision. We estimate that approximately 1% of patients who have a metal-on-metal resurfacing develop a pseudotumour within five years. The cause is unknown and is probably multifactorial. There may be a toxic reaction to an excess of particulate metal wear debris or a hypersensitivity reaction to a normal amount of metal debris. We are concerned that with time the incidence of these pseudotumours may increase. Further investigation is required to define their cause.

Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement.

We examined the relationships between the serum levels of chromium and cobalt ions and the inclination angle of the acetabular component and the level of activity in 214 patients implanted with a metal-on-metal resurfacing hip replacement. Each patient had a single resurfacing and no other metal in their body. All serum measurements were performed at a minimum of one year after operation. The inclination of the acetabular component was considered to be steep if the abduction angle was greater than 55 degrees. There were significantly higher levels of metal ions in patients with steeply-inclined components (p = 0.002 for chromium, p = 0.003 for cobalt), but no correlation was found between the level of activity and the concentration of metal ions. A highly significant (p < 0.001) correlation with the arc of cover was found. Arcs of cover of less than 10 mm were correlated with a greater risk of high concentrations of serum metal ions. The arc of coverage was also related to the design of the component and to size as well as to the abduction angle of the acetabular component. Steeply-inclined acetabular components, with abduction angles greater than 55 degrees, combined with a small size of component are likely to give rise to higher serum levels of cobalt and chromium ions. This is probably due to a greater risk of edge-loading.

Hip resurfacings revised for inflammatory pseudotumour have a poor outcome

Inflammatory pseudotumours occasionally occur after metal-on-metal hip resurfacing and often lead to revision. Our aim was to determine the severity of this complication by assessing the outcome of revision in these circumstances and by comparing this with the outcome of other metal-on-metal hip resurfacing revisions as well as that of matched primary total hip replacements. We identified 53 hips which had undergone metal-on-metal hip resurfacing and required revision at a mean of 1.59 years (0.01 to 6.69) after operation. Of these, 16 were revised for pseudotumours, 21 for fracture and 16 for other reasons. These were matched by age, gender and diagnosis with 103 patients undergoing primary total hip replacement with the Exeter implant. At a mean follow-up of three years (0.8 to 7.2) the outcome of metal-on-metal hip resurfacing revision for pseudotumour was poor with a mean Oxford hip score of 20.9 (sd 9.3) and was significantly worse (p < 0.001) than the outcome for fracture with a mean Oxford hip score of 40.2 (sd 9.2) or that for other causes with a mean Oxford hip score of 37.8 (sd 9.4). The clinical outcome of revision for pseudotumour was also significantly worse (p < 0.001) than the outcome of matched primary total hip replacements. By contrast, the outcome for fracture and other causes was not significantly different from that of matched primary total hip replacements (p = 0.065). After revision for pseudotumour there were three cases of recurrent dislocation, three of palsy of the femoral nerve, one of stenosis of the femoral artery and two of loosening of the component. Five hips required further revision. In three of these there was evidence of recurrent pseudotumour, and one is currently awaiting further revision. The incidence of major complications after revision for pseudotumour (50%) was significantly higher (p = 0.018) than that after revision for other causes (14%). The outcome of revision for pseudotumour is poor and consideration should be given to early revision to limit the extent of the soft-tissue destruction. The outcome of resurfacing revision for other causes is good.

Risk factors for inflammatory pseudotumour formation following hip resurfacing

Metal-on-metal hip resurfacing is commonly performed for osteoarthritis in young active patients. We have observed cystic or solid masses, which we have called inflammatory pseudotumours, arising around these devices. They may cause soft-tissue destruction with severe symptoms and a poor outcome after revision surgery. The aim of this study was to determine the incidence of and risk factors for pseudotumours that are serious enough to require revision surgery. Since 1999, 1419 metal-on-metal hip resurfacings have been implanted by our group in 1224 patients; 1.8% of the patients had a revision for pseudotumour. In this series the Kaplan-Meier cumulative revision rate for pseudotumour increased progressively with time. At eight years, in all patients, it was 4% (95% confidence interval (CI) 2.2 to 5.8). Factors significantly associated with an increase in revision rate were female gender (p < 0.001), age under 40 (p = 0.003), small components (p = 0.003), and dysplasia (p = 0.019), whereas implant type was not (p = 0.156). These factors were inter-related, however, and on fitting a Cox proportional hazard model only gender (p = 0.002) and age (p = 0.024) had a significant independent influence on revision rate; size nearly reached significance (p = 0.08). Subdividing the cohort according to significant factors, we found that the revision rate for pseudotumours in men was 0.5% (95% CI 0 to 1.1) at eight years whereas in women over 40 years old it was 6% (95% CI 2.3 to 10.1) at eight years and in women under 40 years it was 13.1% at six years (95% CI 0 to 27) (p < 0.001). We recommend that resurfacings are undertaken with caution in women, particularly those under 40 years of age but they remain a good option in young men. Further work is required to understand the aetiology of pseudotumours so that this complication can be avoided.

Metal Ion Measurement as a Diagnostic Tool to Identify Problems with Metal-on-Metal Hip Resurfacing

Metal-on-metal bearings for hip replacement are gaining popularity as an alternative to the most widely used bearing couple of metal on polyethylene1. The recent resurgence of hip resurfacing with the so-called third and fourth generations of hip resurfacing arthroplasty devices has played a substantial role in the wider use of metal-on-metal bearings2-4. Concerns about the wear of polyethylene and the role of polyethylene wear debris in the process of aseptic loosening have also increased the use of hard-on-hard bearing couples. However, wear still takes place with metal-on-metal bearings, and there is concern about the relatively high levels of metallic ions released into the body as a consequence. Cobalt-chromium alloy is the metal used for metal-on-metal implants and, while these elements are required for normal biological function, high concentrations of cobalt and chromium are toxic and are known to interfere with a number of biological processes5,6. The metal ion levels typically seen in patients with well-functioning metal-on-metal implants are not thought to be close to toxic levels7 and in many instances are not much higher than those in patients with metal-on-polyethylene implants8. However, there is a potential for much higher concentrations of metal wear products in the joint fluid in the vicinity of the bearing surfaces of poorly functioning metal-on-metal implants. It is these very high levels that are thought to be responsible for adverse reactions such as osteolysis9 and the formation of soft-tissue masses10,11 and that give rise to metallosis (defined as gray discoloration of the hip joint)12. It is not clear whether the levels of metal ions measured in blood serum are indicative of the metal ion concentrations in the joint fluid. Perhaps more importantly, the serum concentrations that are …

Necrotic and inflammatory changes in metal-on-metal resurfacing hip arthroplasties

Background Necrosis and inflammation in peri-implant soft tissues have been described in failed second-generation metal-on-metal (MoM) resurfacing hip arthroplasties and in the pseudotumors associated with these implants. The precise frequency and significance of these tissue changes is unknown. Method We analyzed morphological and immunophenotypic changes in the periprosthetic soft tissues and femoral heads of 52 revised MoM arthroplasties (fracture in 21, pseudotumor in 13, component loosening in 9, and other causes in 9 cases). Results Substantial necrosis was observed in the periprosthetic connective tissue in 28 of the cases, including all pseudotumors, and 5 cases of component loosening. A heavy, diffuse inflammatory cell infiltrate composed mainly of HLA-DR+/CD14+/CD68+ macrophages and CD3+ T cells was seen in 45 of the cases. Perivascular lymphoid aggregates composed of CD3+ cells and CD20+ B cells were noted in 27 of the cases, but they were not seen in all cases of component loosening or pseudotumors. Plasma cells were noted in 30 cases. Macrophage granulomas were noted in 6 cases of component loosening. In the bone marrow of the femoral head, a macrophage and T cell response was seen in 31 of the cases; lymphoid aggregates were noted in 19 of the cases and discrete granulomas in 1 case. Interpretation Our findings indicate that there is a spectrum of necrotic and inflammatory changes in response to the deposition of cobalt-chrome (Co-Cr) wear particles in periprosthetic tissues. Areas of extensive coagulative necrosis and a macrophage and T lymphocyte response occur in implant failure and pseudotumors, in which there is also granuloma formation. The pathogenesis of these changes is uncertain but it may involve both a cytotoxic response and a delayed hypersensitivity (type IV) response to Co-Cr particles.

Minimally invasive Oxford phase 3 unicompartmental knee replacement: results of 1000 cases.

This prospective study describes the outcome of the first 1000 phase 3 Oxford medial unicompartmental knee replacements (UKRs) implanted using a minimally invasive surgical approach for the recommended indications by two surgeons and followed up independently. The mean follow-up was 5.6 years (1 to 11) with 547 knees having a minimum follow-up of five years. At five years their mean Oxford knee score was 41.3 (sd 7.2), the mean American Knee Society Objective Score 86.4 (sd 13.4), mean American Knee Society Functional Score 86.1 (sd 16.6), mean Tegner activity score 2.8 (sd 1.1). For the entire cohort, the mean maximum flexion was 130° at the time of final review. The incidence of implant-related re-operations was 2.9%; of these 29 re-operations two were revisions requiring revision knee replacement components with stems and wedges, 17 were conversions to a primary total knee replacement, six were open reductions for dislocation of the bearing, three were secondary lateral UKRs and one was revision of a tibial component. The most common reason for further surgical intervention was progression of arthritis in the lateral compartment (0.9%), followed by dislocation of the bearing (0.6%) and revision for unexplained pain (0.6%). If all implant-related re-operations are considered failures, the ten-year survival rate was 96% (95% confidence interval, 92.5 to 99.5). If only revisions requiring revision components are considered failures the ten-year survival rate is 99.8% (confidence interval 99 to 100). This is the largest published series of UKRs implanted through a minimally invasive surgical approach and with ten-year survival data. The survival rates are similar to those obtained with a standard open approach whereas the function is better. This demonstrates the effectiveness and safety of a minimally invasive surgical approach for implanting the Oxford UKR.

Metal-on-metal bearings: THE EVIDENCE SO FAR

Lately, concerns have arisen following the use of large metal-on-metal bearings in hip replacements owing to reports of catastrophic soft-tissue reactions resulting in implant failure and associated complications. This review examines the literature and contemporary presentations on current clinical dilemmas in metal-on-metal hip replacement.

Analysis of wear of retrieved metal-on-metal hip resurfacing implants revised due to pseudotumours

The presence of pseudotumours, which are soft-tissue masses relating to the hip, after metal-on-metal hip resurfacing arthroplasty has been associated with elevated levels of metal ions in serum, suggesting that pseudotumours occur when there is increased wear. We aimed to quantify the wear in vivo of implants revised for pseudotumours (eight) and of a control group of implants (22) revised for other reasons of failure. We found that the implant group with pseudotumours had a significantly higher rate of median linear wear of the femoral component at 8.1 microm/year (2.75 to 25.4) than the 1.79 microm/year (0.82 to 4.15; p = 0.002) of the non-pseudotumour group. For the acetabular component a significantly higher rate of median linear wear of 7.36 microm/year (1.61 to 24.9) was observed in the pseudotumour group compared with 1.28 microm/year (0.81 to 3.33, p = 0.001) in the other group. Wear of the acetabular component in the pseudotumour group always involved the edge of the implant, indicating that edge-loading had occurred. Our findings are the first direct evidence that pseudotumour is associated with increased wear at the metal-on-metal articulation. Furthermore, edge-loading with the loss of fluid-film lubrication may be an important mechanism of generation of wear in patients with a pseudotumour.

Transferring simulated arthroscopic skills to the operating theatre: a randomised blinded study.

The aim of this study was to investigate the effect of laboratory-based simulator training on the ability of surgical trainees to perform diagnostic arthroscopy of the knee. A total of 20 junior orthopaedic trainees were randomised to receive either a fixed protocol of arthroscopic simulator training on a bench-top knee simulator or no additional training. Motion analysis was used to assess performance objectively. Each trainee then received traditional instruction and demonstrations of diagnostic arthroscopy of the knee in theatre before performing the procedure under the supervision of a blinded consultant trainer. Their performance was assessed using a procedure-based assessment from the Orthopaedic Competence Assessment Project and a five-point global rating assessment scale. In theatre the simulator-trained group performed significantly better than the untrained group using the Orthopaedic Competence Assessment Project score (p = 0.0007) and assessment by the global rating scale (p = 0.0011), demonstrating the transfer of psychomotor skills from simulator training to arthroscopy in the operating theatre. This has implications for the planning of future training curricula.