Orthopaedic metals and their potential toxicity in the arthroplasty patient

The treatment of femoral neuropathy due to pseudotumour caused by metal-on-metal resurfacing arthroplasty

Concerns now exist about the long-term biological effects of exposure to orthopaedic metal alloys, particularly serum cobalt and chromium ions derived from metal-on-metal wear debris in these patients. A pseudotumour mass complicating metal-on-metal resurfacing arthroplasty has been recognized by orthopaedic oncologists and specialist hip units. Pseudotumours may also present with a major nerve palsy. Two cases of femoral neuropathy due to pseudotumour masses caused by metal-on-metal resurfacing arthroplasty are presented. Preoperative neurophysiological studies showed severe and irreversible pathological changes to nerve function with neurohistopathological evidence of complete nerve destruction with a previously unreported pathological appearance. This may represent a previously unrecognized pathological process, possibly 'toxic' in nature, resulting from metal-on-metal wear debris. Prolonged follow-up and detailed clinical assessment of patients after hip resurfacing arthroplasty is advocated with planned and expeditious revision of any patient in whom evidence of femoral neuropathy develops.

Six-year results of a prospective study of metal ion levels in young patients with metal-on-metal hip resurfacings

We describe the findings at six years in an ongoing prospective clinicoradiological and metal ion study in a cohort of 26 consecutive male patients with unilateral Birmingham Hip Resurfacing arthroplasties with one of two femoral head sizes (50 mm and 54 mm). Their mean age was 52.9 years (29 to 67). We have previously shown an early increase in the 24-hour urinary excretion of metal ions, reaching a peak at six months (cobalt) and one year (chromium) after operation. Subsequently there is a decreasing trend in excretion of both cobalt and chromium. The levels of cobalt and chromium in whole blood also show a significant increase at one year, followed by a decreasing trend until the sixth year.

Unipolar proximal femoral endoprosthetic replacement for tumour

We undertook a cemental unipolar proximal femoral endoprosthetic replacement in 131 patients with a mean age of 50 years (2 to 84). Primary malignant tumours were present in 54 patients and 67 had metastatic disease. In addition, eight patients had either lymphoma or myeloma and two had non-oncological disorders. The mean follow-up was 27 months (0 to 180). An acetabular revision was required later in 14 patients, 12 of whom had been under the age of 21 years at the time of insertion of their original prosthesis. The risk of acetabular revision in patients over 21 years of age was 8% at five years compared with 36% in those aged under 21 years. All the unipolar hips in this younger age group required revision within 11 years of the initial operation.

We conclude that unipolar replacement should not be used in younger patients and should be avoided in patients with a life expectancy of more than five years.

Elektra trapeziometacarpal prosthesis for treatment of osteoarthrosis of the basal joint of the thumb

The first reports about treating osteoarthrosis of the trapeziometacarpal (TMC) joint with the Elektra prosthesis were encouraging. Based on those, we operated on 17 hands in 16 patients with Eaton stage 3+4 osteoarthritis of the TMC joint using the Elektra hydroxyapatite-coated uncemented TMC prosthesis. There were 15 women and one man, mean age 54 years (range 40-70). At follow-up after 35 months (range 22-52), four patients had been reoperated on because of aseptic loosening of the screw cup with migration and progressive pain. Two other patients have been revised because the implant had to be removed for other reasons. At radiological follow-up in the 11 other patients, one cup had migrated and was clearly loose, leaving 10 implants with no sign of failure. Part of this mediocre result may be explained by the learning curve, but more studies are needed to confirm the excellent results obtained elsewhere with the Elektra prosthesis, and we advise others to monitor their results carefully when using this implant. Studies comparing joint replacement with resection arthroplasty are also needed.

Metal-on-metal hip resurfacing arthroplasty: a review of periprosthetic biological reactions

Metal-on-metal hip resurfacing arthroplasty has undergone a recent resurgence as an alternative treatment option for young and active patients with significant osteoarthritis. The claimed advantages of metal-on-metal hip resurfacing arthroplasty include lower wear rate, preservation of bone stock for subsequent revision procedures, restoration of anatomic hip mechanics, and enhanced stability due to the larger diameter of articulation. A disadvantage, however, is that the metal-on-metal resurfacing releases large amounts of very small wear particles and metal ions. The long-term biological consequences of the exposure to these Co-Cr particles and ions remain largely unknown. The purpose of this review is to provide an overview of the current literature on the adverse periprosthetic biological reactions associated with metal-on-metal hip resurfacing arthroplasty.

Femoral neck fracture following hip resurfacing

A total of 20 pairs of fresh-frozen cadaver femurs were assigned to four alignment groups consisting of relative varus (10° and 20°) and relative valgus (10° and 20°), 75 composite femurs of two neck geometries were also used. In both the cadaver and the composite femurs, placing the component in 20° of valgus resulted in a significant increase in load to failure. Placing the component in 10° of valgus had no appreciable effect on increasing the load to failure except in the composite femurs with varus native femoral necks. Specimens in 10° of varus were significantly weaker than the neutrally-aligned specimens.

The results suggest that retention of the intact proximal femoral strength occurs at an implant angulation of ≥ 142°. However, the benefit of extreme valgus alignment may be outweighed in clinical practice by the risk of superior femoral neck notching, which was avoided in this study.

The effect of component size and orientation on the concentrations of metal ions after resurfacing arthroplasty of the hip

Increased concentrations of metal ions after metal-on-metal resurfacing arthroplasty of the hip remain a concern. Although there has been no proven link to long-term health problems or early prosthetic failure, variables associated with high metal ion concentrations should be identified and, if possible, corrected. Our study provides data on metal ion levels from a series of 76 consecutive patients (76 hips) after resurfacing arthroplasty with the Articular Surface Replacement. Chromium and cobalt ion concentrations in the whole blood of patients with smaller (<or= 51 mm) femoral components were significantly higher than in those with the larger (>or= 53 mm) components (p < 0.01). Ion concentrations in the former group were significantly related to the inclination (p = 0.01) and anteversion (p = 0.01) of the acetabular component. The same relationships were not significant in the patients with larger femoral components (p = 0.61 and p = 0.49, respectively). Accurate positioning of the acetabular component intra-operatively is essential in order to reduce the concentration of metal ions in the blood after hip resurfacing arthroplasty with the Articular Surface Replacement implant.

Revision of metal-on-metal resurfacing arthroplasty of the hip: the influence of malpositioning of the components

We have reviewed 42 patients who had revision of metal-on-metal resurfacing procedures, mostly because of problems with the acetabular component. The revisions were carried out a mean of 26.2 months (1 to 76) after the initial operation and most of the patients (30) were female. Malpositioning of the acetabular component resulted in 27 revisions, mostly because of excessive abduction (mean 69.9 degrees ; 56 degrees to 98 degrees ) or insufficient or excessive anteversion. Seven patients had more than one reason for revision. The mean increase in the diameter of the component was 1.8 mm (0 to 4) when exchange was needed. Malpositioning of the components was associated with metallosis and a high level of serum ions. The results of revision of the femoral component to a component with a modular head were excellent, but four patients had dislocation after revision and four required a further revision.

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.

Necrotic granulomatous pseudotumours in bilateral resurfacing hip arthoplasties: evidence for a type IV immune response

Clinical, radiological and histological findings were analysed in four patients who developed bilateral pseudotumours following metal-on-metal (MoM) resurfacing arthroplasties of both hips. Using a panel of monoclonal antibodies directed against HLA-DR, macrophages (CD14, CD68), dendritic cells (DC-SIGN, S100, CD11c), B cells (CD20), and T cells (CD3, CD4, CD8), the nature of the heavy inflammatory response seen in these cases was examined. Bilateral masses developed in periprosthetic soft tissues following the second MoM arthroplasty; these were characterised histologically by extensive coagulative necrosis, a heavy macrophage infiltrate and the presence of granulomas containing macrophages and giant cells; there was also a diffuse lymphocyte and variable plasma cell and eosinophil polymorph infiltrate. Immunohistochemistry showed strong expression of HLA-DR, CD14 and CD68 in both granulomatous and necrotic areas; lymphocytes were predominantly CD3+/CD4+ T cells. The clinical, morphological and immunophenotypic features of these necrotic granulomatous pseudotumours, which in all cases develop following a second resurfacing hip arthroplasty, is suggestive of a type IV immune response, possibly to MoM metal alloy components.

Metal-on-metal hip implants: do they impair renal function in the long-term? A 10-year follow-up study

INTRODUCTION

The aim of our study was to investigate a potential influence of elevated serumcobalt and serumchromiumlevels on renal function at minimum 10 years after implantation of a metal-on-metal hip.

MATERIALS AND METHODS

Between November 1992 and June 1994 98 patients (44 m, 54 f) with an average age of 56 (22-79) years received a metal-on-metal bearing Metasul. At the time of the 10-year follow-up, 15 patients had died and 8 were lost to follow-up. The remaining 75 patients had laboratory analysis including serumcreatinine and full blood cell count as well as chromium and cobalt serum levels.

RESULTS

Ten years postoperatively the median serumcreatinine level was 0.86 (0.55-1.51) mg/dl, the serumcreatinine clearance Ccr was in the normal range. The hemogram did not differ from that measured at the time of surgery. The median serumcobalt concentration was 0.75 (0.3-50.10) microg/l and the serumchromium concentration was 0.95 (0.3-58.6) mug/l, 10 years postoperatively.

CONCLUSION

Our long-term data do not show any influence of serum cobalt or chromium concentrations on renal function following total hip arthroplasty.

[Hip resurfacing: current state of knowledge]

SUMMARY

The tribologic quality of metal-on-metal bearings has enabled a second generation of hip resurfacing techniques. Compared with a conventional hip prosthesis, this type of arthroplasty has many advantages: sparing femoral (and acetabular) bone stock, preservation of hip joint biomechanics (femoral offset, leg length), better recovery for high-level sports activities, easier revision, less risk of dislocation, less risk of extension to the shaft in the event of osteolysis. Hip resurfacing can thus be considered as true "minimally invasive bone surgery". There are however specific complications of resurfacing, including femoral neck fracture and collapse of the femoral head. All of the conventional approaches can be used for hip resurfacing procedures, but a precise operative technique is mandatory. The key to success is a proper position of the femoral piece. Certain biomechanical rules for implantation are required in order to limit the cam effect, spare femoral bone, and maintain harmonious loading. Hip resurfacing can be indicated for young and/or active subjects for whom restoration of hip biomechanics offers a real advantage over conventional hip arthroplasty. The mid-term results have been encouraging, both clinically and radiographically.

Biocompatibility evaluation of a novel hydroxyapatite-polymer coating for medical implants (in vitro tests)

Nanocomposites consisting of hydroxyapatite (HA) and a sodium maleate copolymer (maleic polyelectrolyte), synthesized by hydrothermal method and deposited on titanium substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique were tested for the biological properties. Coating bioanalysis was carried out by triple staining of actin, microtubules and nuclei followed by immunofluorescence microscopy. Within 24 h cells that occupied the biomaterial surface displayed the morphology and cytoskeleton pattern similar to the controls. Cells grown on nanocomposite coated surfaces had a higher proliferation rate than their counterparts grown on Ti coated with HA alone, indicating that maleic polyelectrolyte improved surface bio-adhesive characteristics. The capacity to induce cell attachment, spreading and proliferation demonstrated the potential of Ti coated with HA-polymer nanocomposites to be used as scaffolds in dental or orthopedic implantology.

Chromium, cobalt and titanium metallosis involving a Nottingham shoulder replacement

Metallosis after shoulder replacement has not previously been described in the literature. We report a patient who developed extensive metallosis after implantation of an uncemented Nottingham shoulder replacement. He underwent a revision procedure. Examination of the retrieved prosthesis showed that the titanium porous coating was separating from the humeral stem and becoming embedded in the ultra-high-molecular-weight polyethylene glenoid component, resulting in abrasive wear of the humeral component. There was metallosis despite exchange of the modular humeral head. Both components had to be exchanged to resolve the problem.

The results of primary Birmingham hip resurfacings at a mean of five years. An independent prospective review of the first 230 hips

We report an independent prospective review of the first 230 Birmingham hip resurfacings in 212 patients at a mean follow-up of five years (4 to 6). Two patients, one with a loose acetabular component and the other with suspected avascular necrosis of the femoral head, underwent revision. There were two deaths from unrelated causes and one patient was lost to follow-up. The survivorship with the worst-case scenario was 97.8% (95% confidence interval 95.8 to 99.5). The mean Harris hip score improved significantly (paired t-test, p < 0.05) from 62.54 (8 to 92) pre-operatively to 97.7 (61 to 100) at a mean of three years (2.1 to 4.3), then deteriorated slightly to a mean of 95.2 (47 to 100) at a mean of five years. The mean flexion improved from 91.5 degrees (25 degrees to 140 degrees) to 110.4 degrees (80 degrees to 145 degrees) at a mean of three years with no further improvement at five years (111.2 degrees; 70 degrees to 160 degrees). On radiological review at five years, one patient had a progressive lucent line around the acetabular component and six had progressive lucent lines around the femoral component. A total of 18 femoral components (8%) had migrated into varus and those with lucent lines present migrated a mean of 3.8 degrees (1.02 degrees to 6.54 degrees) more than the rest. Superolateral notching of the femoral neck and reactive sclerosis at the tip of the peg of the femoral component were associated with the presence of lucent lines (chi-squared test, p < 0.05), but not with migration of the femoral component, and are of unknown significance. Our results with the Birmingham hip resurfacing continue to be satisfactory at a mean follow-up of five years.

Chronic inflammation, joint replacement and malignant lymphoma

This paper considers the increased risk of the development of lymphoma in patients with chronic inflammatory disease who undergo metal-on-metal arthroplasty.

The validity of serum levels as a surrogate measure of systemic exposure to metal ions in hip replacement

Metal ions generated from joint replacements are a cause for concern. There is no consensus on the best surrogate measure of metal ion exposure. This study investigates whether serum and whole blood concentrations can be used interchangeably to report results of cobalt and chromium ion concentrations.

Concentrations of serum and whole blood were analysed in 262 concurrent specimens using high resolution inductively-coupled plasma mass-spectrometry. The agreement was assessed with normalised scatterplots, mean difference and the Bland and Altman limits of agreement.

The wide variability seen in the normalised scatterplots, in the Bland and Altman plots and the statistically significant mean differences between serum and whole blood concentrations suggest that they cannot be used interchangeably. A bias was demonstrated for both ions in the Bland-Altman plots. Regression analysis provided a possible conversion factor of 0.71 for cobalt and 0.48 for chromium. However, even when the correction factors were applied, the limits of agreement were greater than ±67% for cobalt and greater than ±85% for chromium, suggesting that serum and whole blood cannot be used interconvertibly. This suggests that serum metal concentrations are not useful as a surrogate measure of systemic metal ion exposure.