Medical devices are hot news at the moment. The PIP breast implant scandal is likely to run and run, the way that devices are regulated is under scrutiny, and the merest whiff of a problem with any one of the thousands of devices on the market is likely to make headline news in the coming months. As long as we are able to keep a sense of proportion this will be no bad thing. If you are in possession of a suspect piece of medical technology then you have the right to know what might go wrong, and the news media is one of the most efficient ways of disseminating this information. And regulation has to be in place to protect patients and ensure that problems are picked up early – although we must resist the temptation to so entwine the industry with rules that we strangle innovation and fail to help the patients of the future.
The scare that has followed on from the PIP scandal (which I have already blogged on here) concerns metal on metal hip replacements. Both scenarios involve a surgical prosthesis, but this is where the similarities end. PIP implants are a true scandal – sub-standard implants were developed to save cost, using silicone that had not been cleared for medical use. Metal on metal hips are a scare, because they have caused problems that were not expected, but they were genuinely developed in an attempt to find a better device. The holy grail of hip surgery is to develop a joint that can last as long as the joint it is replacing – and that we are so far from reaching this goal is testament to the astonishing engineering inherent in the joints we are born with. Most hip replacements are a metal head in a plastic cup. Since the metal is the strongest part of this combination, it seemed logical to use this material for both parts of the artificial joint. Early experience was encouraging, and these hips were especially used in younger patients who had the most to gain from a long-lasting joint.
So what has been the problem? Well it is not that the joints are breaking – they seem to be as strong as promised. The difficulty is that, in a small number of people, tiny metallic shavings are coming away from the surface where the two components rub together. This is not weakening the joint, but the fragments are being absorbed into the surrounding tissues, where they make a considerable nuisance of themselves. Mostly this causes inflammation around the joint, and so pain starts to develop in a joint that had been performing well. This will not be sudden, but will come on gradually over weeks and months. In a small number of case reports the metal has been dispersed more widely, and led to high levels of cobalt or chromium in the blood, and associated toxicity. Symptoms have included neurological problems, such as tinnitus, vertigo, anxiety and depression, and memory problems, and also cardiac problems such as heart failure and high blood pressure, and so although this is rare, it is potentially quite worrying. In most cases these more general problems occur in people who have pain in the joint, but in at least one case reported in the British Medical Journal recently there was no pain in the joint – although the joint was inflamed when the patient underwent surgical revision.
The risk to patients is quite different to the situation with PIP breast implants. The implants are at an uncertain risk of a one-time sudden event, which is rupture of the implant. This means that a woman with a fully functioning implant might be well today, and have suffered from a rupture tomorrow. Although the consequences of rupture are not life-threatening, this uncertainty can be difficult to live with. The situation with hip replacements is more straight-forward, although potentially much more serious. A patient with a metal on metal hip who feels well, and has no pain in the hip, need not worry, and certainly won’t want to consider surgery to replace a joint that is working well. On the other hand, if it is causing problems, then revision surgery may well need to be considered – which is quite a significant thing to have to face.
The Medicines and Healthcare products Regulatory Agency (MHRA) has issued guidance concerning these implants, as has the British Orthopaedic Association. The consensus view is that the majority of patients will not have a problem and do not need any special investigations. However, all patients should be followed up at least annually for the first five years, and have easy access to prompt follow-up should they develop symptoms. Where symptoms do occur there should be imaging of the joint (MRI scanning or ultrasound) and measurement of blood cobalt and chromium levels. Where revision surgery is needed it may be difficult due to the inflammation, and so should be performed by a surgeon experienced in revisions. For anyone who has had a hip replacement and is not sure of the type of joint they have, they should contact the orthopaedic surgeon who performed the surgery who will be able to advise on the type of joint used.