BMJ 2011;343:d7441 doi: 10.1136/bmj.d7441 (Published 29 November 2011)
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Practice
PRACTICE PRACTICE POINTER
Diagnosing and investigating adverse reactions in metal on metal hip implants Use of metal bearings in hip replacements and resurfacing operations has led to adverse reactions to metal debris in many patients. This article examines how to assess and manage any patient with a metal on metal total hip replacement who presents with potential joint failure 1
2
Camdon Fary clinical fellow consultant orthopaedic surgeon , Geraint Emyr Rhys Thomas clinical 3 1 3 research fellow , Adrian Taylor consultant orthopaedic surgeon honorary senior clinical lecturer , 3 David Beard professor of musculoskeletal sciences , Andrew Carr Nuffield professor of orthopaedic 13 1 3 surgery , Sion Glyn-Jones consultant orthopaedic surgeon clinical senior lecturer Nuffield Orthopaedic Centre, Oxford OX3 7LD, UK; 2Royal Melbourne and Western Hospitals, Melbourne, Victoria, Australia; 3Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Biomedical Research Unit into Musculoskeletal Disease, University of Oxford, Nuffield Orthopaedic Centre, Oxford, OX3 7LD, UK 1
Promising five year results in 2005 for large diameter “metal on metal” hip replacement surgery1 led to a rapid increase in the number of surgeons performing this procedure and in orthopaedic companies competing to produce their own resurfacing designs. Adverse reactions to metal debris were not anticipated or predicted.
Over 250?000 large diameter, metal on metal, articulating total hip replacements (most of which are resurfacing procedures) have now been performed worldwide.2 UK and Australian national joint registries have reported statistically significant increased revision rates for specific metal on metal total hip replacements compared with conventional metal on plastic total hip replacements.3-5 Adverse soft tissue reactions to the debris released by metal on metal implants (metal wear debris) may result in the early failure of these implants and a need for revision surgery. Although adverse reactions to such debris can present with few symptoms, lesions may be highly locally destructive, which makes revision surgery challenging.
Recently a specific metal on metal implant was recalled internationally, which has resulted in a review of the evaluation, introduction, and regulation of new medical devices (BMJ 2011;342:d2905, doi:10.1136/bmj.d2905). However, some patients with failed implants may not yet have presented to practitioners with silent or symptomatic adverse reactions to devices, and the incidence of failed metal on metal hip replacements is likely to be cumulative. This may become an important health and economic burden on patients and commissioners of healthcare respectively.
We review the assessment and management of any patient with a metal on metal total hip replacement who presents with potential joint failure. We draw from recent guidelines, the evidence in the literature (which is limited to case-control, cohort, and case studies), and our own experience.
What is a metal on metal hip replacement?
A metal on metal hip replacement refers to the type of articulating bearing surface that was designed as an alternative to conventional metal on polyethylene bearings. The metal is specially hardened and composed of cobalt chrome alloy.
The metal on metal articulating bearing is used in two distinctly different femoral prosthetic designs: as a large metal femoral head on a standard femoral stem or as a large metal femoral head cemented on to the native bone of the femoral neck (hip resurfacing).
Why have metal on metal articulating surfaces been used? The metal on metal bearing surface has been used to treat younger and more active patients, with excellent results reported in some case series.6 Reported benefits of hip resurfacing include lower theoretical rate of dislocation associated with large diameter heads than with conventional metal on polyethylene total hip replacement; low wear; bone conservation; physiological femoral loading; and improved restoration of joint mechanics. Case series have suggested that revising a hip
Correspondence to: C Fary, Western Hospital, Footscray, Victoria, Australia
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BMJ 2011;343:d7441 doi: 10.1136/bmj.d7441 (Published 29 November 2011)
Page 2 of 5
PRACTICE
Summary points Large diameter, metal on metal bearings may be used in hip replacement and hip resurfacing operations Early evidence suggested that metal on metal implants were more resistant to wear and tear and dislocation; consequently they were often used in younger and more active patients Adverse reactions to metal debris can result in the formation of a mass lesion that can be locally invasive around the joint. Such lesions may be difficult to diagnose as many are silent Symptomatic patients may complain of discomfort in the hip or buttock; a swelling in the hip region; pain in the hip; or clicking or “giving way” of the hip Ultrasound scanning by a skilled operator, followed by magnetic resonance imaging when a lesion is detected, will lead to a diagnosis in most cases Revision surgery is usually indicated. Revision after adverse reaction to metal debris has a poorer outcome than revision for other indications
resurfacing procedure to a standard total hip replacement conserves more bone than a revision of a conventional hip replacement.7
What are the problems associated with metal on metal articulating surfaces? Inflammatory changes
Observed soft tissue inflammatory reactions to metal wear debris have been called inflammatory pseudotumour,8 adverse reaction to metal debris,9 aseptic lymphocytic vasculitis associated lesion,10 and metallosis.11 Inflammatory pseudotumour is a clinical description of a mass (hence tumour) that may be cystic or solid (hence pseudo) in association with clinical, radiological, and histolopathological findings consistent with inflammation. Subtle differences between different prosthetic designs are believed to play a role in increased wear and subsequent metal debris. One particular hip resurfacing device, the articular surface replacement (ASR) hip resurfacing device, has been shown in a large multicentre cohort study to have a much higher rate of failure attributed to adverse reactions to metal debris than other resurfacing devices.9 The ASR hip resurfacing device has a shallower acetabular component, resulting in greater edge loading and wear than with other designs.
Histology The findings of a case series suggest that a spectrum of necrotic and inflammatory changes occur in response to the deposition of particles released by cobalt-chrome prosthetic wear into the periprosthetic tissues.12 The pathogenesis of these changes is uncertain but may involve both a cytotoxic response and a delayed hypersensitivity (type IV) response to cobalt-chrome particles.[10 ]Adverse reactions can be caused by large amounts of wear debris but have also been shown to occur around implants with small amounts of wear debris.9 Retrieval studies of failed components show that most failures of components are the result of increased wear, suggesting a toxic aetiology. A smaller number of failures may result from hypersensitivity reaction with normal wear.9
How common are adverse reactions? The true incidence of adverse reactions to metal wear debris is not known as they are difficult to diagnose and are therefore probably under-reported. Four per cent of masses are thought to be asymptomatic initially,13 and magnetic resonance imaging studies have shown that “silent” pathology exists (25% of patients with a best possible Oxford hip score had evidence of adverse reactions to metal debris confirmed by magnetic resonance imaging).14
For personal use only: See rights and reprints http://www.bmj.com/permissions
Designer series (series performed by surgeons involved in the design process) suggest a cumulative revision rate of
