Large-diameter metal-on-metal hips were thought to be an independent risk factor in hip failure, besides the material from which the prosthetic was made. But according to a recent study, adverse reactions to metal debris from small-headed metal-on-metal Articular Surface Replacement (ASR) hips are even more common than originally thought.
In the study, 482 hips (424 patients) were reviewed. After the ASR small-diameter hip was recalled at an average of 4.9 years post-op, 379 patients (435 hips) agreed to a screening that measured cobalt and chromium in the blood.
Metal-on-metal hip implants are created with a ball-and-cup design made up of a cobalt-chromium alloy. When the parts rub together during normal use, the hip sheds metal ions, which can pollute the bloodstream and damage the surrounding tissue.
When metal ions from the debris leach into the blood stream, cobalt and chromium toxicity can occur, which is linked to symptoms such as high blood pressure, dizziness, skin rashes, tremor, poor coordination, cognitive decline and depression. The toxicity has also been linked to damaging effects on the heart, hearing and vision.
A total of 162 hips (34 percent) were revised, the majority of which were due to adverse reactions to metal debris shed by the hip implant. Only 41 percent of the small-diameter ASR hips survived more than seven years. The study concluded that the small-diameter hip is an independent risk factor for hip implant failure.
Metal-on-metal hip implant manufacturers such as Wright Medical, DePuy Orthopaedics and its parent company Johnson & Johnson, Stryker, Smith & Nephew and Zimmer Biomet Holdings have thousands of lawsuits filed against them alleging the devices have resulted in injury to the patients, most of whom experienced some level of cobalt toxicity and/or poisoning. DePuy Orthopaedics is facing 8,900 lawsuits in the U.S. alone over the allegedly faulty hip designs.