Without any human testing or detailed follow-up studies, metal-on-metal implant manufacturers started tweaking the design of their implants. One popular change was to increase the size of femoral heads.
A recent British Medical Journal article states these changes had "unforeseen consequences." To this day, Biomet touts its M2a Magnum (speaking of bigger size!) for its large head which allegedly provides stability. However, the British Medical Journal points out that studies show increased wear and higher levels of metal ions in tissue and the blood.
DePuy and Zimmer have also pushed hip replacement implants with larger heads and acetabular cups. The article concludes that "fast tracking" approval and week regulation needs to be 'tweaked' itself.