A shocking intraoperatively diagnosis of ochronotic knee arthropathy: a case report.

Introduction: Alkaptonuria is an autosomal extremely rare recessive metabolic disorder with incidence reported to occur as 1:100 000-1:250 000 live births worldwide. This rare metabolic disorder is characterized by the accumulation of homogentisic acid due to a deficiency in homogentisic acid 1,2 dioxygenase. Homogentisic acid subsequently oxidizes and accumulates in the connective tissue. The knee is the most significant peripheral joint to be affected by the disorder. The authors present the first case of ochronotic arthropathy in Syria. Case presentation: A 46-year-old male presented with bilateral pain in the knees. the pain was affecting his day-to-day activities, and not responding to conservative management. Anteroposterior standing radiographs demonstrated extensive degenerative disease. Intraoperatively, the diagnosis was done after noticing that the quadriceps tendon and the articular cartilage of the femur, tibia, and patella were blackened during cemented total knee replacement of the knee. Conclusion: Ochronotic arthropathy should be kept in mind in middle age patients with severe osteoarthritis to not be surprised by the rare alkaptonuria diagnosis if arthroplasty was indicated.