Metal Debris Wears Off from another Part of Metal-on-Metal Hip Implants
07/12/2011 04:59
Aside from the shallow cup, recent medical studies have confirmed that metal ions and debris could come from another part of metal-on-metal hip implants especially those manufactured by the DePuy Orthopaedics Inc. According to medical experts interviewed by the New York Times, the shallow cup design of the DePuy Articular Surface Replacement (ASR) hip implant was said to be the culprit why the device fails five years 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. DePuy is also having the same problems abroad with at least 300 hip replacement lawsuits also 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. The cup’s shallow design and the removal of the plastic liner from the inside of the implant were done by DePuy 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. Implants with large diameter metal femoral heads is where this problem is often noted probably because these heads cause more force to be channeled through the taper junction between the head and the stem. Aside from DePuy, a large diameter head could also be found in metal-on-metal hip implants manufactured by 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. One of the tapers retrieved from a patient gave researchers further evidence of wear and corrosion. The findings prompted the researchers’ conclusion that using large diameter metal bearings in total hip replacements may be inappropriate.
The filing of DePuy ASR lawsuit is seen to continue especially with this new finding. Court documents have shown that nearly 20 lawsuits in connection with the DePuy hip replacement recall are filed every day in the United States.
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