Alkaptonuria is caused by the defective metabolism of homogentisic acid, which causes arthritis and connective tissue pigmentation. The knee is a commonly affected joint. Total knee arthroplasty (TKA) has been suggested as an effective treatment for end-stage ochronosis arthropathy. A case of a 62-year-old man presented with pain in both knee joints and X-rays revealed advanced degenerative arthritis. During knee replacement, the subcutaneous tissues revealed blackish nodules. It was difficult to retract the patella as the patella tendon was stiff and hard with blackish discoloration. On dislocating patella, the patella tendon was avulsed on the right knee; later, it was fixed with a suture anchor and stapler. To avoid patella tendon avulsion, we did a tibial tuberosity flip osteotomy on the left knee. Ochronosis arthropathy should be considered as a diagnosis when faced with black connective tissue intraoperatively. Surgeons should anticipate patella tendon avulsion and difficulties in soft tissue balancing in the onchronitic knee and ready to tackle the complications.