Studies have shown that pseudotumors are as much as ten times more common in patients with metal-on-metal hip devices or those hip implants which have metal components such as Stryker’s Rejuvenate and ABG II. A study published in the Journal of Bone and Joint surgery noted a significantly higher rate of the development of pseudotumors among those patients with metal hip implants. The Stryker Rejuvenate and ABG II models were recalled in July, 2012 after findings of early failure as well as risks of corrosion and fretting. This Stryker hip replacement recall has subsequently led to lawsuits against the company after patients developed hip implant problems, metal poisoning, chromium and cobalt toxicity and pseudotumors.
The Stryker models introduced a new design which utilized a modular neck-stem taper allowing surgeons to better fit the hip implant to the individual patient’s size and activity level. This design was not a true metal-on-metal implant rather used ceramic components with a metal neck juncture and metal trunnions located on either end of the neck piece. These metal parts were not expected to produce metal shear like the all-metal implants therefore it was dismaying to realize that corrosion could still occur at the neck juncture and beneath the metal trunnions. This corrosion can cause pseudotumors—benign solid or semi-liquid masses which, although not an infection and not cancerous can nonetheless lead to tissue necrosis.
When pseudotumors form it is necessary to have them removed in order to minimize tissue damage. Generally, by the time pseudotumors have formed there will also be other noticeable adverse health issues such as cobalt and chromium toxicity or implant failure. Therefore a revision surgery may be performed at the same time the pseudotumor is removed. The American Journal of Orthopedics detailed the case history of a 64-year old man who had undergone hip replacement surgery one year prior to the time he sought medical help due to pain in the groin and thigh area, difficulty walking and stiffness and inflammation in the hip region. Tests were performed including an MRI and bone scan. Physicians believed pseudotumors could be responsible for the patient’s symptoms.
Revision surgery was scheduled, and once an incision was made a “significant amount of fluid erupted from the acetabulum and a large soft tissue membrane sac was visualized.” The pseudotumor was removed, and it was subsequently determined through fluid analysis that there was no infection involved. Unfortunately, the pseudotumor had caused significant tissue necrosis, leaving the short external rotators only minimally attached. The hip implant device was removed and it was noted that noticeable corrosion was present on the neck and stem body. Due to the extreme level of tissue and bone loss, two metal cables were required to attach the new implant, and bone was recreated with demineralized bone matrix putty. The patient was sent home to recuperate for six weeks, with instructions to put no weight on the hip and was doing well at a follow-up visit with cobalt and chromium levels decreasing with time.
Pseudotumors may also be called cysts, masses or fluid collections, and while the pathology is not entirely clear, it is believed they are inflammatory reactions to the metal debris which sheds from the metal parts of the Rejuvenate hip implant device or from other metal-on-metal implants. Some experts believe the pseudotumors from when edge loading from mal-positioned components occurs, while others attribute the cysts to metal sensitivity of the individual patient. Women are more likely to develop pseudotumors, possibly due to the difficulty in positioning the components in a smaller body. In any case, when a person with a metal-on-metal hip implant or a Stryker Rejuvenate or ABG II hip device experience pain or swelling in the hip region yet their physician determines the implant is well-positioned, a pseudotumor could have occurred in the hip region. Surgical intervention will be necessary to prevent any further tissue loss; should the patient also have significantly elevated cobalt and chromium levels revision surgery will be likely.