Spontaneous Achilles tendon rupture as the initial presentation of ochronosis: a case report

Introduction: Alkaptonuria (AKU) is a rare autosomal recessive metabolic disorder characterized by homogentisic acid accumulation leading to ochronosis, which weakens connective tissues and may rarely affect tendons. Presentation of case: A 43-year-old man presented with sudden right ankle pain and functional loss without preceding trauma. Examination revealed a palpable gap and pigmentation of the sclera and ear. Intraoperatively, the Achilles tendon was friable and black. Histopathology confirmed ochronotic degeneration. Surgical repair using a modified Krackow suture with intraosseous anchoring achieved stable fixation and uneventful recovery. Discussion: This case illustrates spontaneous Achilles tendon rupture as an initial manifestation of AKU. Oxidative stress-induced collagen degeneration leads to tendon fragility. Recognition of characteristic pigmentation and histological features is essential for diagnosis. Conclusion: Ochronosis should be considered in unexplained tendon ruptures. Surgical repair and metabolic management, including nitisinone, can optimize outcomes.