A metal-on-metal hip device sits inside a metal liner with a metal ball that works at the top of the thigh bone (femoral head) and acts as a replacement socket. From 2006 on, implants had a higher risk of revision in comparison with those manufactured before 2006. The revisions were due to variations in the manufacturing process between batches, researchers felt.
Researchers looked specifically at the long-term performance of the 36 mm Pinnacle metal-on-metal hip in an effort to uncover the risk factors that lead to early failure and the need for further surgery. Pinnacle is the most commonly implanted metal hip in the world, according to BMJ Open.
Of the identified patients, 489 had Pinnacle hips: 243 women and 191 men participated. In a review, 352 attended recall clinics where they underwent clinical examination, blood metal ion measurement, X-rays, and targeted imaging as needed. Patients were monitored for an average of 7.5 years, post-surgery. Of these hips, 71 had to be surgically removed and replaced. “This device was found to have an unacceptably high revision rate,” researchers said, reported BMJ Open.
Before 2006 only 5 out of 43 hips (12 percent) failed to meet the manufacturer’s product specification. But, after 2006, more than 36 percent (43 out of 118) failed to comply.
In over 40 percent of cases examined, the taper surface was defective. The taper surface is the inside of the femoral head that is attached to the femoral stem and is the part that anchors the implant in the thigh bone. This defect was associated with excessive metal particle release. This could lead to metallosis, or metal poisoning. The symptoms are bone and tissue death, implant failure, and severe pain, according to drugwatch.