Quadriceps tendon rupture as the initial presentation of undiagnosed alkaptonuria (ochronosis): A rare case report

Quadriceps tendon rupture is an uncommon injury, usually associated with systemic or local risk factors. Alkaptonuria, a rare metabolic disorder, causes ochronotic pigment deposition in connective tissues, leading to early degeneration and tendon fragility. We report a 49-year-old man presenting with sudden inability to extend his right knee after a trivial trauma. Magnetic resonance imaging confirmed complete quadriceps tendon rupture at the patellar insertion with retraction. Intra-operatively, the tendon appeared darkly pigmented and friable, consistent with ochronosis. Primary repair with transosseous sutures restored full extension, and the patient had good functional recovery. Subsequent evaluation demonstrated spinal disc calcification and urine discoloration on standing, confirming alkaptonuria. This case highlights that ochronosis may present as spontaneous tendon rupture in undiagnosed patients. Recognition of intraoperative pigment changes offers a vital diagnostic clue, and orthopedic surgeons should maintain a high index of suspicion for metabolic disorders in atypical tendon pathology.