Total knee replacement for ochronotic arthritis: A rare case report

Total knee replacement (TKR) is commonly performed for managing advanced osteoarthritis. There are several causative factors of osteoarthritis, from degenerative processes associated with age to rare genetic disorders correlated with a rare course of disease and remained undetected even until adulthood. Herein, we present a case of ochronotic arthritis characterized by black discoloration of the articular cartilage, meniscus, and soft tissue surrounding the right knee, which was detected during TKR, in a patient with alkaptonuria. This is a rare case and managing the patient require conscientious approach. For the past four years, a 64-year-old man had been experiencing chronic right knee pain. During admission, the patient was limping and unable to bear weight on the affected knee. The right knee was swollen, with limited range of motion and audible crepitation during flexion. Radiography revealed narrowing of the joint space and osteophytes on the articular surface. Further investigation showed that the patient was previously diagnosed with alkaptonuria and was scheduled for TKR. Intraoperatively, we found that the articular cartilage, meniscal surface, and soft tissue surrounding the knee had black discoloration. Thus, additional debridement of soft tissues was required. Alkaptonuria may increase the risk of osteoarthritis in the knee joint. Ochronosis correlated with alkaptonuria. Diagnosis can be conducted with physical examination, synovial fluid exam and complete urinalysis to avoid misdiagnose of this disease. In our study, TKR for ochronotic arthritis had good outcomes, with a knee score of 95 and a function score of 90. The patient received routine treatment for alkaptonuria at the Urology Department. •Alkaptonuria result in the accumulation of homogentisic acid in collagenous structure.•Articular cartilage may experience mild discoloration due to deposition of hemosiderin and lipofuscin.•Degenerative process result in joint arthrosis or pain, and reduced range of motion in the affected joint.•TKR for ochronotic arthritis had good outcomes.