Thousands of patients with the DePuy ASR™ metal-on-metal hip replacement (recalled in 2010) have filed lawsuits when their hip replacements failed prematurely due to the production of metal ions and debris. Initially it was believed that most of the metal ions and debris were created by edge loading of the femoral head against the perimeter of the acetabular cup. More recently however, studies are demonstrating what had been suspected for some time – that wear and corrosion of the taper junction between the tip of the femoral stem and the base of the femoral head was also producing dangerous metal debris. This appears to be a problem particularly with large diameter metal femoral heads probably because these heads cause more force to be channeled through the taper junction between the head and the stem.
In one recent study published in The Journal of Bone & Joint Surgery, researchers found evidence that patients with large diameter head metal-on-metal hip replacement systems made by DePuy (ASR™), Zimmer (Durom®), Biomet (M2a-Magnum™) and Smith & Nephew (BHR) had significantly higher blood levels of cobalt metal ions than did patients with smaller diameter metal femoral heads. The authors also found evidence of wear and corrosion in one of the tapers retrieved from a patient. The researchers concluded that use of large diameter metal bearings in total hip replacements may be inappropriate.
A second study also published in The Journal of Bone & Joint Surgery studied 185 patients with large-diameter metal-on-metal hip replacements with a mean implant time of approximately five years. The authors, Bolland and others, found that these metal-on-metal hip replacements showed an unacceptably high rate of failure (including those awaiting surgery, a 15% failure rate), evidence of high wear at the trunnion-head interface, evidence of metallosis (adverse reaction to metal debris), and passive corrosion of the stem surface, raising more concerns about these types of metal on metal hip replacements.
These studies suggest that the metal wear, metallosis and tissue damage and higher failure rates associated with the DePuy ASR™ hip replacement (recalled) may be a problem in other similar large-diameter head metal-on-metal hip replacement systems with modular tapers such as the DePuy Pinnacle® hip replacement system, the Zimmer Durom® hip replacement system (recalled), and the Biomet M2a-Magnum™ hip replacement system.
