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. The DePuy’s Articular Surface Replacement (ASR) hip implant’s shallow cup design was said to be the reason why the device fails five years after it has been implanted, said medical experts in an interview with the New York Times. Thousands of lawsuits filed against DePuy and its mother company Johnson & Johnson in the United States used as basis the hip implants’ premature failure. DePuy is also having the same problems abroad with at least 300 hip replacement lawsuits also filed in Britain.

 

Microscopic ions of heavy metal chromium and cobalt are the result of edge loading of the femoral head against the perimeter of the DePuy acetabular as initially shown by medical studies. 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. However, instead of doing just that, the 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.    

 

Aside from the shallow cup, studies conducted recently 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.

 

The Journal of Bone & Joint Surgery had published a recent study wherein researchers found evidence that patients implanted with hip devices that have a large diameter head had significantly higher blood levels of cobalt metal ions than patients with smaller diameter metal femoral heads. One of the tapers retrieved from a patient gave researchers further evidence of wear and corrosion. With this, researchers reached a conclusion that the use of large diameter metal bearings in total hip replacements may be inappropriate.

 

With this new finding, there is no reprieve seen in 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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