Degenerative arthritis of the knee secondary to ochronosis.

Alkaptonuria is a rare disease in which a deficiency in the homogentisate 1, 2-dioxygenase enzyme results in a buildup of homogentisic acid. Ochronosis, the deposition of excess homogentisic acid in connective tissue, causes brownish-black pigmentation and weakening of the tissue ultimately resulting in chronic inflammation, degeneration, and osteoarthritis. There is currently no definitive cure for alkaptonuric ochronosis, and management is usually symptomatic. However, total joint replacements in severe cases of ochronotic osteoarthritis have comparable outcomes to osteoarthritic patients without ochronosis. We report a case of a patient with ochronotic arthritis of the knee treated with total knee arthroplasty.