Metal-on-metal hip replacements implanted since 2006 have had a higher rate of manufacturing issues, with over one-third of hips manufactured outside the stated specification possibly to blame, researchers suggest.
Specifically, the 36 mm DePuy Pinnacle device, the most commonly implanted metal hip in the world, was researched for its long-term performance, and the need to reveal the risk factors associated with its early failure and the necessity for further surgery, says the online journal BMJ Open.
The use of metal-on-metal hips has declined in the last five years, but “hundreds of thousands” remain in place. With continuing research bringing better understanding of the factors contributing to the failures, not only would the design of future products benefit, it would help those patients already fitted with the implants.
The DePuy Pinnacle hip device sits inside a metal liner with a metal ball that works at the top of the thigh bone (femoral head) acting as a replacement socket. Total replacement of both (bilateral) hip joints and thinner liners were risk factors for failure at nine years.
Researchers reviewed the progress of 434 patients: 243 women and 191 men. They were fitted with 489 metal-on-metal total hip replacements at a hospital in northern England and monitored for an average of 7.5 years following the procedure.
The result was 71 metal hips had to be surgically removed and replaced, meaning a revision rate of 16.4 percent, which was described by the researchers as “unacceptably high.” Before 2006, only 12 percent (5 out of 43) of the hips failed to meet the manufacturer’s product specifications. After 2006, more than a third (43 out of 118) failed to comply. Abundant metal staining of tissues (metallosis) had occurred in around one in five (19 percent) cases, BMJ Open reports.