Local tissue reaction and necrosis-induced femoral nerve palsy in a patient with a metal-on-metal total hip arthroplasty: a case report.

This case report describes a 54-year-old Hispanic male who developed femoral nerve palsy approximately 1 year after metal-on-metal total hip arthroplasty (MOM THA). Cobalt and chromium levels were 4.8 ppb and undetectable, respectively. MRI demonstrated a well-encapsulated pseudotumor that communicated with the anterior portion of the right hip, and EMG showed neuropraxic femoral nerve injury. As a result, the patient experienced motor and sensory loss in the femoral and proximal saphenous nerve distributions. Surgical revision to ceramic-on-poly THA with debridement and decompression of the pseudotumor improved the patient's neurological status. Similar acute local tissue reactions have been described but the serum levels of cobalt and chrome associated with these reactions have been variable. Wear particles and products produced from corrosion at the head taper junction from MOM THA can potentially lead to cellular dysfunction with subsequent pseudotumer formation, but these reactions and fluid collections have also been found. In this patient, serum cobalt levels were elevated, while serum chromium levels remained undetectable. The purpose of this case report is to describe one patient's response and to review the recent literature regarding potential complications of MOM THA.