Man's rare disorder causes cartilage, joints to become black A 52-year-old man has a unique condition in which his joints and cartilage are turning a color they should not be - dark black. The New England Journal of Medicine chronicled the unnamed patient's struggles in their latest online issue. The man, who suffers from large-joint arthropathy, needed both his right knee replaced, as well as a shoulder joint replacement following trauma. In both surgeries, the man's knee joints and shoulder joints appeared to be black. Not only did the man's joints turn black, but other body parts turned the dark shade too. The man's sclera - the white parts of his eyes - also had dark pigmentation and his ear cartilage had a blue tinge to it. The patient reported that throughout his life, his urine often turned a dark color once it was exposed to oxygen. This kind of pigment deposition is a familiar symptom of ochronosis - a condition in which excess homogentisic acid accumulates in the body's connective tissues. Deposited as an ochre-colored pigment in bone, cartilage and skin, the acid ultimately causes the bluish-black hues. The disorder can also cause degenerative arthritis. Ultimately, the patient underwent and aortic-valve replacement to help correct the condition. He has been receiving the drug nitisinone, which reduces the amount of homogentisic acid in his system.