Intraoperative Findings in Total Hip Arthroplasty Leading to a Diagnosis of Alkaptonuria in a Patient With Severe Hip Osteoarthritis Initially Attributed to Rheumatoid Arthritis: A Case Report

Alkaptonuria is a rare inherited condition caused by elevated levels of homogentisic acid, which confers a characteristic dark color on tissues like cartilage and bones over time, a process known as ochronosis. We present the case of a 62-year-old male patient with a presumed diagnosis of rheumatoid arthritis and severe pain and stiffness in his right hip. Plain radiographs revealed severe right hip osteoarthritis. The patient underwent total hip arthroplasty (THA) without any perioperative complications. The intraoperative findings (black ring-like spot at the femoral head and also at the cartilage and acetabulum) and a more detailed medical history taken postoperatively raised suspicions of alkaptonuria, which was confirmed with the specific exam for alkaptonuria (homogentisic acid levels evaluation in a 24 h urine sample). This report underscores the importance of a thorough medical history and clinical examination of these patients to avoid inaccurate diagnosis and administration of inappropriate therapeutic schemes.