Knee Arthroplasty in Alkaptonuric Arthropathy

Alkaptonuria is a rare autosomal recessive genetic disorder that causes accumulation of homogentisic acid (HGA) due to loss of homogentisate 1,2-dioxygenase (HGD) activity. Large amounts of HGA excreted in the urine turn the urine dark upon exposure to air. Deposition of HGA polymers, which are oxidized into a melanin-like pigment, discolors and degenerates connective tissues and also leads to ochronosis. The most common clinical consequence of HGA polymer deposition is ochronotic arthropathy, which does not differ in clinical presentation from other degenerative arthropathies. The disease not only involves joints, but also the spine, kidney, and cardiovascular system. We report a case of ochronotic arthropathy that was misdiagnosed as traumatic joint arthritis in the right knee. The patient was informed that data concerning the case would be submitted for publication, and he provided consent. A fifty-seven-year-old man (height, 165 cm; weight, 53 kg) presented with a six-month history of difficulty walking because of pain in the right knee. He had a three-year history of pain in both knees. Two years prior to presentation, he had undergone arthroscopic bilateral cruciate ligament reconstruction; he also had undergone an internal fixation of the right femur because of a low-energy fracture three months after the cruciate ligament reconstruction. We initially diagnosed traumatic arthritis in the right knee (Fig. 1). While performing a total knee arthroplasty, we observed that the joint cartilage in the right knee was dark in color and that there was scattered pigmentation of the tendon and the meniscus (Fig. 2). Large prostate stones were visible on the postsurgical radiographs (Fig. 3) . Histology of the tissue removed during arthroplasty revealed black cartilage (Fig. 4). Fig. 1 Preoperative anteroposterior (left image) and lateral (right image) knee radiographs showing apparent traumatic knee arthritis. A locking plate and artificial ligament can also be observed. Fig. 2 At …