Following the Stryker hip replacement recall in July, 2012, more questions have arisen regarding the formation of pseudotumors, metal poisoning and chromium and cobalt toxicity. Hip implant problems have rapidly become the rule rather than the exception, particularly among those with all-metal implants or implants such as the Rejuvenate and ABG II which have metal components. Research has indicated that pseudotumors are also much more likely among those with hip implants which contain chromium or cobalt. In one analysis, the only significant predictor for pseudotumors was serum cobalt levels above 5 µ/ml; patients with elevated cobalt levels were four times more likely to develop pseudotumors than those with lower levels after adjusting for age, gender, allergies and other factors.
Pseudotumors can range from small to very large and are typically solid or semi-liquid masses which form in the area around the artificial hip device. The exact reason these pseudotumors form is not entirely clear, but it is believed the formation of the tumors is a reaction to a foreign body whether the implant is metal, polyethylene or ceramic. Metals in the hip implant, particularly among those who are especially sensitive to metals, can make the formation of pseudotumors more likely. It is advisable for anyone considering the implantation of a hip device constructed of metal to have a metal sensitivity test done prior to the surgical procedure.
While the pseudotumor mass may be able to be seen through the skin, in many cases there are few indications of the pseudotumor’s presence until the patient develops significant pain in the hip joint, inflammation or limited mobility. In fact, by the time a pseudotumor is diagnosed, it may have been present for a significant length of time, causing tissue destruction. A pseudotumor can mimic the effects of infection however they are neither infective nor cancerous.
Although the Rejuvenate and ABG II are not true metal-on-metal hip implants, they contain a metal neck juncture as well as metal trunnions. During the Stryker hip replacement recall the company noted a particular risk of fretting, corrosion and early failure among the devices. This corrosion causes microscopic metal ions to shear away from the device, lodging in the hip tissue or entering into the bloodstream. Chromium and cobalt toxicity can occur when the levels of these dangerous metals build up and when the shards burrow into tissue, inflammation, pain, bone loss and degradation of tissue can occur.
Metal poisoning can cause a wide variety of medical problems, many of them extremely serious or even life-threatening. Gastrointestinal, neurological, cardiovascular, thyroid and renal disorders can occur, loss of memory, loss of vision or hearing, skin disorders, anxiety, depression, irritability and even DNA disruption can all occur following implantation of an implant which incorporates metal in the design. Both issues can lead to revision surgery—a potentially risky and complex operation which leaves the patient with a significantly longer recovery time than the original hip implant surgery.
Research has shown that in addition to metal sensitivity as a factor in pseudotumors, women appear to have a higher risk of developing pseudotumors due to the smaller hip implant components used which have been associated with increased wear. These smaller hip device components are also less forgiving of being misaligned. When pseudotumors are present they must be removed and it is likely the hip implant will need to be removed and replaced with a non-metal implant. All recipients of hip implant devices should undergo tests to determine the presence of pseudotumors as well as the presence of metal poisoning.
Research suggests that pseudotumors are as much as ten times more common in those patients with metal-on-metal hip devices, including Stryker’s Rejuvenate and ABG II which are constructed with metal parts. One study, published in the Journal of Bone and Joint surgery noted a “substantially higher” rate of soft-tissue mass development (pseudotumors) in recipients of metal hip implants than previously identified. In one particular study, 3.6 years following surgery showed 42 out of 108 patients in the study had pseudotumors—nearly 39%.