The black humeral head

A middle aged patient with a history of prior lower extremity joint replacements presented with a painful stiff shoulder and these x-rays. While they show narrowing of the joint space, the osteophyte formation and the sclerosis typical of osteoarthritis are lacking.

The patient desired a total shoulder arthroplasty. At this procedure a black humeral head was seen

A standard total shoulder with a canal-sparing impaction grafted humeral prosthesis was used.

This patient has alkaptonuria, an autosomal recessive inherited condition that causes urine to turn black when exposed to air. The HGD gene provides instructions for making an enzyme called homogentisate oxidase. This enzyme helps break down the amino acids phenylalanine and tyrosine. Mutations in the HGD gene impair the enzyme's role in this process. As a result, a substance called homogentisic acid, which is produced as phenylalanine and tyrosine are broken down, accumulates in the body. Excess homogentisic acid is deposited in connective tissues, which causes cartilage and skin to darken. Over time, a buildup of this substance in the joints leads to arthritis. Homogentisic acid is also excreted in urine, making the urine turn dark when exposed to air. Affected individuals typically develop arthritis of the spine and large joints after the age of 30. Ochronosis refers to the buildup of blue-black pigment in connective tissues such as cartilage and skin, which is typical of this disorder.  Other features can include heart problems, kidney stones, and prostate stones.

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