BMJ 2011;343:d7441

Diagnosing and investigating adverse reactions in metal on metal hip implants

Camdon Fary, clinical fellow1, consultant orthopaedic surgeon2, Geraint Emyr Rhys Thomas, clinical research fellow3, Adrian Taylor, consultant orthopaedic surgeon 1, honorary senior clinical lecturer3, David Beard, professor of musculoskeletal sciences3, Andrew Carr, Nuffield professor of orthopaedic surgery13, Sion Glyn-Jones, consultant orthopaedic surgeon1, clinical senior lecturer3

Hip

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

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

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 4 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 resurfacing procedure to a standard total hip replacement conserves more bone than a revision of a conventional hip replacement.7

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