Ochronotic Arthropathy of the Knee: A Case Report

Alkaptonuria (AKU) is a low-prevalence genetic inherited disease expressed in an autosomal recessive and monogenic manner, characterized by a tissue accumulation of homogentisic acid (HGA). It is more severe in male patients, with arthritic symptoms as the earliest clinical picture in most cases.

This enzyme deficiency metabolic disorder causes an increase in HGA, an intermediary in the metabolism of amino acids normally excreted in the urine. Homogentisic aciduria can be observed in patients with alkaptonuria, manifested by darkening of the first-morning urine. Ochronosis, a tissue homogentisic acid accumulation, progresses with connective tissue pigmentation and severe ochronotic joints osteoarthropathy. Ochronosis can also occur in the eyes, ears, skin, and heart valves. Also, are seen blackened kidneys and prostate stones, injuries to muscles and tendons, as well as fractures.

We present a case report of a 60-year-old male patient who previously underwent two arthroscopies of the left knee due to pain with no predefined etiology.

After a year, he sought a referral orthopedic hospital complaining of diffuse pain and persistent edema due to severe lateral femolotibial and patellofemoral osteoarthritis and valgus deformity.

Total arthroplasty of the left knee was indicated and performed, with a suspected diagnosis of ochronosis intraoperatively and confirmed with additional tests. The patient has been followed up for 2 years after left knee arthroplasty, with a favorable outcome.