A rare condition in which the ligaments and cartilages of the body, and sometimes the conjunctive (see EYE), become stained by dark brown or black pigment. This may occur in chronic carbolic poisoning, or in a congenital disorder of metabolism in which the individual is unable to completely break down tyrosine in protein molecules – the intermediate product, homogentisic acid, appearing in the urine, this being known as alkaptonuria.