The widespread use of the metal-on-metal hip implant has expanded the use of the term “pseudo-tumor” to describe a (usually) non-infectious, non-cancerous, space-occupying tumor in the hip region. Research done in the Netherlands found that recipients of metal-on-metal hip implants had four times the risk of developing a pseudo-tumor when they presented with elevated serum metal ion levels, and that 28% of those with metal-on-metal hip implants in the study did develop a pseudo-tumor.7 Pseudo-tumors are generally thought to occur more often in those patients who have a hypersensitive reaction to cobalt and chromium ions.
In many cases, those with all-metal hip implants may be unaware of the pseudo-tumor until it has grown quite large; depending on where the tumor is located, the patient may have developed hip or groin pain, swelling in the upper leg or the foot and ankle region, a clicking or popping noise in the hip area, a nerve disorder which leads to weakness or immobility, or a discernible lump in the hip. Pseudo-tumors resulting from metal-on-metal hip implants can grow rapidly, becoming larger than an orange and can be accompanied by bone loss and chronic, sometimes severe, pain. Pseudo-tumors can even place pressure on surrounding body structures, leading to other serious health issues.
Surgeons have noted that in some cases pseudo-tumors have exploded when opened up during surgery. Pseudo-tumors are not cancer or even an indication of a precancerous condition, however they are serious and can result in revision surgery or further health problems. A metal hip implant which is less-than-perfectly positioned is more likely to create the best environment for pseudo-tumors, therefore the margin for surgical error is slim. Smaller-boned women with shallower hips are also more likely to develop pseudo-tumors. Subtle changes in x-rays could be an indication of a developing pseudo-tumor as could groin and hip pain. X-rays, blood tests and a multi-slice CT scan may all be used to determine the presence of a pseudo tumor, and in some instances aspiration of the hip joint could be warranted to rule out infection.
ALVAL
Pseudo-tumors are one type of soft-tissue mass resulting from a metal-on-metal hip implants, and ALVAL (aseptic lymphocyte dominated vasculitis associated lesion) is another. While ALVAL is not fully understood, it is believed it may result from bone dissolution. Tissue necrosis is a key feature of ALVAL, although the symptoms vary. Patients suffering from ALVAL may be diagnosed when asked by their physician to perform a straight-leg raise. In most of those with ALVAL, this exercise will be extremely painful. Many ALVAL patients tend to have pain in the groin area, though not all. When a patient is suspected of having AVAL, the physician may aspirate fluid from the hip area.
This fluid will usually be thick and grey-green in color among those suffering from ALVAL. Research suggests that one possible cause of ALVAL is misalignment of the meal-on-metal hip implant. This incorrect placement leads to undue amounts of wear on the implant device, which in turn leads to corrosion and the generation of excess ion debris. Many physicians knowledgeable in metal-on-metal hip implants believe ALVAL is under-diagnosed due to the somewhat non-specific symptoms. Revision surgery may be warranted, depending on the severity of the ALVAL.