Second Source Of Metal Debris Uncovered In Metal-on-Metal Hip Implants
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 implant’s shallow design as being at the heart of the device’s five year-failure after it has been implanted. This premature failure of the hip implants is the basis of the thousands of lawsuits that have been filed against DePuy and its mother company Johnson & Johnson in the United States. DePuy is also having the same problems abroad with at least 300 hip replacement lawsuits also filed in Britain.
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Earlier, medical studies have suggested that microscopic ions of heavy metals chromium and cobalt were created by edge loading of the femoral head against the perimeter of the DePuy acetabular cup. DePuy designed a shallower cup and removed the plastic liner from the inside of the implant to give its patients a wider range of motion. The new design only made the hip implant susceptible to edge loading, a situation wherein the joint’s ball strikes against the cup’s 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, recent studies have demonstrated that wear and corrosion of the taper junction between the tip of the femoral stem and the base of the femoral head also produced dangerous metal debris. 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. DePuy’s 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.
A study published recently in the Journal of Bone & Joint Surgery showed that 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. Researchers also found evidence of wear and corrosion in one of the tapers retrieved from a patient. The findings prompted the researchers’ conclusion that using 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.
References:
depuyhipreplacementlawsuit.com/depuy-hip-replacement-lawsuit-status-conference-this-month/
world.einnews.com/pr_news/59900568/asymptomatic-metal-on-metal-hip-replacement-patients-may-still-be-experiencing-tissue-damage
forthepeople.com/depuy-metallosis-depuy-hip-implant-recall–12-3189.html
nytimes.com/2010/03/10/business/10device.html
nytimes.com/2010/03/04/health/04metalhip.html
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