The dark side of cartilage: ochronosis unmasked during femoral neck fracture surgery

Abstract

Alkaptonuria is a rare autosomal recessive disorder caused by a deficiency in homogentisic acid oxidase, leading to the accumulation of homogentisic acid in connective tissues. It is characterized by bluish-black pigmentation of cartilage and other connective tissues, with progressive joint degeneration and early-onset osteoarthritis. Ochronosis typically becomes symptomatic after the age of 30, affecting larger joints and the spine. A 75-year-old female presented with a transcervical femoral neck fracture and a right distal end radius fracture following a fall. During hip surgery, intraoperative findings included blackish discoloration of the femoral head and acetabulum. The patient had a history of stooped posture and calcified intervertebral discs. Further examination revealed ochronotic pigmentation of the sclera and ear cartilage, and a urine test confirmed the diagnosis of ochronosis. Postoperative recovery was uneventful. Ochronosis should be considered in the differential diagnosis of patients with calcified intervertebral discs and early-onset joint degeneration. The condition is typically asymptomatic until joint involvement occurs. Current treatment options are limited, though nitisinone and dietary modifications show some promise. This case highlights the importance of recognizing ochronosis in patients with joint degeneration, particularly when intraoperative findings reveal characteristic pigmentation.