Another Part Of Metal-on-metal Hip Implants Also Found As Source Of Metal Debris

Recent medical studies confirmed suspicions that another part of metal-on-metal hip

implants especially those manufactured by the DePuy Orthopaedics Inc. is also the source of metal ions and debris aside from the shallow cup. A New York Times report stated that medical experts pointed at the DePuy Articular Surface Replacement (ASR) hip implants shallow design as being at the heart of the devices five year-failure after it has been implanted. Thousands of lawsuits that were filed against Johnson & Johnson and its subsidiary DePuy in the United States involved the premature failure of the hip implants. DePuys problem is not just contained within the U.S. as at least 300 hip replacement lawsuits have also been filed in Britain.

Initial medical studies showed that edge loading of the femoral head against the perimeter of the DePuy acetabular cup resulted into the wearing off of microscopic ions of heavy metals chromium and cobalt. To provide its patients with a wider range of motion, DePuy made its cup design shallower and removed the plastic liner from the inside of the implant. The new design only made the hip implant susceptible to edge loading, a situation wherein the joints ball strikes against the cups edge and causes the implant parts to rub together and chisel off microscopic ions of the heavy metals chromium and cobalt into the body.

However, recently conducted studies proved that dangerous metal debris could also come from the wear and corrosion of the taper junction between the tip of the femoral stem and the base of the femoral head. This problem is noted particularly in implants 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. DePuys metal-on-metal hip implant is not the only one with a large diameter head, it could also be found in the hip devices of Zimmer, Biomet and Smith & Nephew.

According to researchers, patients who had hip implants that have a large diameter head had significantly higher blood levels of cobalt metal ions than patients with smaller diameter metal femoral heads and this finding was published recently in the Journal of Bone & Joint Surgery. Researchers also found evidence of wear and corrosion in one of the tapers retrieved from a patient. These findings had researchers concluding that use of large diameter metal bearings in total hip replacements may be inappropriate.

The new finding will further drive on the filing of DePuy ASR lawsuit. Nearly 20 lawsuits in connection with the DePuy hip replacement recall are filed every day in the United States, according to court documents.

by: Nancy

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