Lessons of a hip failureBMJ 1998; 316 doi: https://doi.org/10.1136/bmj.316.7132.644 (Published 28 February 1998) Cite this as: BMJ 1998;316:644
If we want improved prostheses we must regulate their use
- Sarah K Muirhead-Allwood, Consultant in revision and hip reconstructive surgery
News p 650
The hazard warning issued this month by the Medical Devices Agency in Britain on the 3M Capital hip system evoked emotion but no surprise among hip surgeons.1 Previous reports of failures have suggested the need for better surveillance,2 and five years ago a BMJ editorial warned, presciently, “This ‘fashion trade’ in joint replacements is costing the health service many millions of pounds each year and, even more important, is causing patients unnecessary pain and distress through early failure of unproved implants.”3 The 3M Capital hip was introduced in 1991 as a low cost hip replacement. Adverse reviews have already been reported, and its failure rates of 19-21% at five years1 are four times what would normally be expected and suggest an intrinsic problem. Yet over six years 4669 have been implanted in 95 centres throughout Britain. For a new and untested hip to have ben introduced into so many clinical centres in such a short period highlights the lack of regulation of both the orthopaedic industry and orthopaedic surgeons.
One response to the failure of the Capital hip is to insist that only old tested designs should be used. Hips such as the Charnley prosthesis, when inserted into patients in the sixth decade of life, will survive for 10 years in 90% of cases, for 20 years in 70%, and for 30 years in 50%. 4 5 Yet not all units using this prosthesis will achieve such good rates of survival, for the longevity of any hip depends not only on prosthetic design but also on surgical technique. If we want to ensure good results we may also need to insist that hip replacement is performed only by specialist hip surgeons. Moreover, the argument for using only tested designs implies they are so good there is no need to try to improve on them. This argument does not apply to drugs: nor should it to prostheses. But drugs are introduced into clinical practice only after extensive clinical trials and a licensing process, and their introduction is accompanied by postmarketing surveillance. None of these apply to prostheses.
The need for improved prostheses is clear. Younger patients have long life expectancies and require more durable prostheses that will last for 30 years or more. In any hip replacement debris disease poses the biggest problem: the body's cellular response to tiny particles of polyethylene from the socket, metal from the prosthesis, or cement produces a reaction that destroys bone. It can occur in patients with mechanically well fixed joints and may be asymptomatic. The process can occur with any artificial joint and is the strongest argument for all hip replacements being kept under radiological review so that, if necessary, revision can be performed as soon as possible. In practice the need for such long term review is continually challenged by budget holders. The Medical Devices Agency is advising all patients with Capital hips to undergo clinical and radiological review.
Huge amounts of energy have been spent by research departments to counter aseptic loosening and debris disease. Modern designs of uncemented sockets will reliably osseointegrate in the pelvis, and the addition of better surface finishes and hydroxyapatite ceramic coatings to uncemented femoral stems now means that they are at least equal to their cemented counterparts in terms of function and durability. The weakest link in joint replacement is the bearing surface, which has traditionally been metal on plastic. Other bearing surfaces using ceramic on plastic, metal on metal, or ceramic on ceramic have smaller wear rates (Mckellop H et al, 10th annual symposium of International Society for Technology in Arthroplasty, San Diego, 1997).6 Much research is carried out worldwide to develop and validate new technology, with mechanical testing, finite element analysis, and animal experimentation. But, as with drugs, a prosthesis can only really be tested when it is used in patients.
If we are to combine improvement with safety we have to find a better way than the present system of introducing new prostheses—which is no more evidence based than the fashion industry.3 New designs should be introduced only in specialist centres, where careful follow up and special research methods, such as early migration measurements, can reveal problems before huge numbers have been inserted. Such formal evaluations of safety and efficiacy should then be followed by the prosthesis being licensed for wider use—though there should still be a requirement for surgeons to record standard data on all their joint operations. Younger patients with longer life expectancy and higher functional demands should be referred to specialist units. And surgeons who do not have a special interest in joint replacement should use only well tried and tested joints. Orthopaedic surgeons have made previous calls for better regulation of the “hip industry.”3 Now that such a failure has happened, the public will not forgive a failure to act.