Ochronotic Knee Arthropathy: A rare cause of arthritic knee pain and literature review of surgical considerations during knee arthroplasty

Introduction: Knee osteoarthritis is a common disabling affection in the elderlies. Rarely the arthritis of knee may be due to ochronotic arthropathy. It is often missed or misdiagnosed as osteoarthritis. An autosomal recessive metabolic disorder characterized by the deficiency of homogentisic acid oxidase enzyme preventing metabolism of homogentisic acid lead to homogentisic aciduria. Alkaptonuria progresses to ochronotic degeneration and arthritis. Early management of ochronotic arthropathy is challenging and is mainly limited to control of symptoms. Advanced cases may necessitate surgery. Case Report: A 65-year-old male presents with persistent progressive pain in both knees, not responding to conservative measures. Patient required simultaneous bilateral cemented total knee arthroplasty for management of arthritic knee pain. Arthrotomy revealed black joints with pigment deposition throughout the articular cartilage and neighboring tissues. Meticulous surgical technique allowed uneventful procedure. Postoperatively patient gained pain-free functional knee movements and was able to ambulate without support within six weeks of arthroplasty. The Knee Society Score improved to 95 bilaterally. At two years, radiologically there was good alignment with no loosening. Discussion: Arthroplasty is an excellent choice for patients with ochronotic arthropathy. However, more information and experience are needed for uniform implant selection and techniques. We report this rare, often missed cause of common knee pain. We review the literature to discuss the specific surgical considerations during knee arthroplasty in such an unusual presentation. Keywords: Alkaptonuria, Ochronosis, Arthropathy, Black joints, Knee arthroplasty..