Ochronotic arthropathy: pathological evidence of acute destruction of the hip joint.

Alcaptonuria is a hereditary disease, also known as black hip, where there is an accumulation of homogentisic acid pigmentation in joint cartilages. We describe a 74-year-old woman who showed acute destruction of her left hip joint. She received a total hip arthroplasty on her right side in July 2000, and was diagnosed with ochronosis. Her postoperative follow-up was at our institutions outpatient department. She first complained of increasing groin pain in July 2005, after which she had a left total hip arthroplasty in October 2005. Histopathologically, samples from this patient showed "fragmentation and cleft formation" in the cartilage of the femoral head. In addition, the samples revealed a remarkable degradation of proteoglycan, which is the secondary most abundant constituent of extra cellular matrix. These findings suggested that "cleft formation", where cracks develop toward the center, caused an acute destructive arthropathy with morphological fragility suggestive of ochronosis.