In this feature, AAOS Now publishes a series of images, challenging readers to diagnose the condition depicted. The images for this month’s challenge were submitted by Stuart J. Fischer, MD, who provides the following information:

The patient is a 50-year-old male who presents with an acute injury to his right knee. He states that he injured his knee with a golf swing and felt acute pain on the medial side. Examination reveals medial tenderness, decreased range of motion, and pain with rotation. MRI shows a large tear of the medial meniscus and early degenerative changes.

The patient has a history of a transient ischemic attack in his 40s, interstitial lung disease, and thrombocytopenia. He is taken to the operating room, and arthroscopy is performed. At surgery, he is noted to have a displaced flap tear of the medial meniscus and degenerative changes in the medial compartment. However, the meniscal tissue, as well as the articular cartilage, are noted to be pigmented with a dark blackish color on the surfaces.

What’s your diagnosis?

Read on for the answer to this month’s challenge.

Answer

The diagnosis is ochronosis, a systemic condition caused by deposition of homogentisic acid in articular cartilage and connective tissues such as tendon and ligaments. This leads to dark, hyperpigmented, “caviar-like” lesions in the affected areas. The exogenous form can be caused by overuse of skin-lightening cream and prolonged sun exposure. An endogenous form, sometimes known as alkaptonuria, results from a genetic mutation and is passed on as an autosomal recessive trait.

The exogenous form of ochronosis is characterized by the presence of pigmented lesions in areas around the face and neck. Diagnosis can be confirmed by biopsy of the lesions or surface microscopy. Alkaptonuria can be diagnosed by the presence of homogentisic acid in urine. Often urine will turn black on standing.

Treatment of ochronosis, particularly alkaptonuria, is largely symptomatic. Stiffness and calcification are known to occur in the joints of the spine and intervertebral disks, often resulting in chronic back pain. Arthritis can develop in major joints such as the hip and knee and require joint replacement.

Systemic complications can include urinary calcification, resulting in stones, and calcification of heart valves, causing the need for valve replacement.