According to a study in bmj.com, the risk of developing cancer within the first seven years after receiving a metal-on-metal hip replacement is no higher than in the general population, although further long-term studies are required.

BBC Newsnight and the BMJ recently investigated potentially high levels of toxic metals from failing hip implants that could affect thousands of people worldwide in the future. The authors also investigated as to why these hip replacements were permitted, regardless of the fact that the risks have been known and documented for decades. The BMJ has a comprehensive range of articles regarding the safety of medical devices that can be viewed here.

The investigation was commissioned by the National Joint Registry of England and Wales, which contains over one million procedures from more than 97% of orthopedic units, and executed by researchers from the Universities of Bristol and Exeter, who investigated the validity of these concerns. To evaluate the success rates of joint implant patients, the registry data and hospital statistics are linked each year.

The authors decided to compare cancer rates in patients with metal-on-metal hip replacements with patients with other types of hip implants, as well as with the general population. 40,576 registered patients in total, i.e. 14% had some kind of metal-on-metal bearing surface, whilst 21,264 patients or 7% had a stemmed metal-on-metal prosthesis and 19,312 patients or 7% had a resurfacing procedure.

The authors compared patient outcomes by using mathematical models that included the patient’s age and sex, as well as three measures of the patient’s general health at the time of hip surgery, i.e. the American Society of Anesthesiologists grade, which scores the patient’s other serious illnesses, the number of NHS funded hospital admissions within the previous five years as well as the number of distinct diagnostic codes recorded at time of surgery.

According to the authors, a comparison between hip replacement patients with people in the general population is not really straightforward, given that hip replacement patients “tend to be healthier than others of the same gender and age group”.

The outcome of the study demonstrated that the likelihood of a 60 year old man of moderate health and a metal-on-metal stemmed hip replacement will be diagnosed with cancer five years after surgery is 6.2% as compared with a likelihood of 6.7% in men with hip replacements that contain other bearing surfaces. In women, these figures were 4.0% and 4.4% for other bearing surfaces respectively.

The findings furthermore reveal that the incidence of diagnosed cancers after hip replacements is low, whilst that predicted for the age and sex of the matched general population is lower.

The authors believe that their study will assist clinicians in reassuring their patients that the “risk of cancer for hip replacement patients is relatively low” and that there is no evidence that metal-on-metal hip replacements pose a higher risk of cancer.

The authors recognize that the results only include findings for up to seven years after surgery and recommend that further long-term data analyses will be performed over the next few decades, given that this is the lead-time for some cancers to develop.

Written by Petra Rattue