DePuy Orthopedics, along with their parent company, Johnson & Johnson, issued a recall of their ASR XL Acetabular Hip System, along with the ASR Hip Resurfacing System in August of 2010. This recall was implemented following a flurry of adverse event reports among recipients of one of these two hip implants. At the time of the recall DePuy and Johnson and Johnson acknowledged that the ASR XL and the ASR Hip Resurfacing System had a higher-than-expected rate of failure—as much as 12% within a short time after implantation. At the time of the recall, DePuy stated that the ASR could loosen or misalign and that recipients of the ASR were at a higher risk for infection, bone fracture, dislocation, metallosis, metal toxicity and pain.
A further phenomenon known as edge loading can occur when the implant cup is set at a less-than-optimal angle. This causes the ball to press the inside of the cup unevenly, placing increased pressure on the cup edges. This increased pressure can lead to excessive wear which, in turn, leads to microscopic ions of cobalt and chromium shearing away into the body. These sloughed-away metal shards will either lodge in the surrounding tissues or travel into the bloodstream. When the tissues become infected with metal ions this can lead to severe inflammation, destruction or death of the tissues or even bone loss. When the surrounding tissues and bone deteriorate, the hip joint can loosen, fracture, and total failure is experienced.
According to the latest research the smaller diameter ASR heads—typically used in women—put the recipient at an even greater risk of metallosis. Despite the issues experienced by DePuy regarding the ASR, over 93,000 ASR implant devices have been installed across the globe since 2003. The ASR XL Acetabular System was approved in 2005 through the controversial 510(k) FDA approval process. This means there was less required safety testing done prior to approval based on the fact that the ASR was substantially equivalent to another device already on the market. The ASR XL Acetabular Hip System is comprised of a ball, socket and neck; a rod coming off the artificial neck is inserted into the shaft of the femur during implantation.
The ASR Hip Resurfacing System was a relatively new technique in the United States and even though both devices share the same cup and ball design (the part that would ultimately prove to be flawed) DePuy was made to conduct clinical trials on the Resurfacing System. During the clinical trials for the ASR Hip Resurfacing System, more femur fractures occurred than expected and although DePuy eventually withdrew their application for FDA approval, the ASR continued to be sold in other countries and U.S. surgeons could choose to implant the device for “off label” use.
Even though the metal-on-metal hip implants offer certain benefits over their plastic or ceramic counterpart, a large number of the all-metal hip implants have suffered issues with metallosis and metal toxicity. A study (which did not specifically target DePuy’s ASR) reported in the Journal of Bone and Joint Surgery stated that patients with all-metal hip implants had cobalt levels as much as 39 times the normal levels and chromium levels as high as twenty-eight times the normal levels.
Metal toxicity can lead to emotional disturbances such as depression, anxiety and irritability, neurological issues such as memory loss, renal, thyroid and cardiovascular problems, decrease in vision and hearing, vertigo, chronic pain, skin problems, gastrointestinal disturbances, inflammation, muscle tissue degeneration, and pseudo-tumor growth. It is extremely likely that any recipient of an ASR all-metal hip implant will experience some level of metallosis or metal toxicity as a result of cobalt and chromium buildup. All metal hip implant patients should ensure their doctor monitors the level of metals in their bloodstream regularly and conducts any other test the doctor feels is warranted.