Massive Pseudotumor Despite Normal Serum Metal Ions in Metal-on-Metal Total Hip Arthroplasty

The development of periprosthetic soft tissue reactions is a well-documented complication in patients who have previously undergone metal-on-metal (MoM) total hip arthroplasty (THA). Adverse reactions resulting from the shedding of intraarticular metal ions have been broadly classified into several modes of failure, including pseudotumor development and aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL). We present a case report of a 76-year-old female with a history of MoM THA who presented with left thigh pain and swelling. Radiographic and histologic analysis were consistent with ALVAL and pseudotumor, despite normal serum metal ion levels. The patient underwent revision total hip arthroplasty with pseudotumor debridement of 3300 mL cystic fluid, and at nearly five years postoperatively, is functioning well with no recurrence of pain or swelling. Review of the literature demonstrates an average pseudotumor area of 73 cm2. Further literature review reveals that serum metal ion levels may not reliably exclude clinically significant pseudotumor formation. As such, this case report challenges the assumption of elevated serum metal ions as an indicator for MoM failure by demonstrating a massive pseudotumor in the context of normal serum levels. Clinicians should maintain a high index of suspicion for adverse local tissue reactions in patients with MoM THA, regardless of serum metal ion levels. Advanced imaging and clinical correlation remain essential for diagnosis and management.