Metal-on-metal hip implants have come under intense scrutiny in the past few years, starting with DePuy’s worldwide recall of its ASR hip implants in 2010. The recall, which was issued because the implant was failing at high rates, was followed by other metal-hip device recalls and thousands of personal injury lawsuits. Traditional hip implants consist of an artificial ball and socket inserted into a patient’s hip joint. In metal-on-metal hip implants, both of these components are made of metal. According to Tech Times, one lawsuit filed in Britain alleges that complications from the DePuy Pinnacle hip implant are due to incorrect sizing.
Metal-on-metal hip implants have become controversial in light of high-profile recalls and complaints of issues such as inflammation and crippling pain. Metal hip devices are also worrisome because they can release metal ions into the body when the metal surfaces of the implant rub together. When complications get severe, the implant fails and patients need to undergo a revision surgery to replace the device. Metal-on-metal hip implants have been linked to high rates of failure compared to other types of hip replacements.
Shedding of metal particles is more likely to occur if the components of the implant do not fit together properly. According to a lawsuit filed at the High Court, DePuy Synthes found an “error in measuring technique” at a plant reportedly based in Leeds that led to adverse effects for patients. The suit says certain parts of the implant were measured while hot, which is different from the measurement at room temperature.
According to Tech Times, DePuy argues that their Pinnacle hip implant is accurate within 32 microns. A 2008 investigation found that slight inaccuracies will not affect the implant liners’ function or lead to health problems. Surgeons, however, say even a small difference in measurement can have significant implications for patients. “When the components are implanted they are matched. If there is a difference in the size it doesn’t have to be very much at all, you will change the wear characteristics,” said British Orthopaedic Association’s former president Tim Briggs, according to Tech Times. On the same note, orthopedic professor Edward Davis said measuring the ball component at 80 degrees Celsius while measuring the socket at 30 degrees Celsius can be potentially detrimental for patients.
Vice president of Royal College of Surgeons and honorary consultant for the Royal National Orthopaedic Hospital Stephen Cannon says problems can arise when components of a device are ill-fitting, regardless of whether a hip implant is all-metal or a combination of metal and plastic. The wear rate increases with mismatched components. The National Health Service (NHS) advises patients with a metal-on-metal hip implant to lookout for symptoms such as: pain in the hip, leg or groin, limping, inflammation near the hip, grinding, chest pain, difficulty breathing, numbness, weakness, changes in hearing or vision, feeling cold and weight gain. Experiencing these symptoms does not necessarily mean that the implant has failed, but NHS does advise a checkup.