Atypical location of an osteoid osteoma with atypical anterior knee pain.

Introduction: An osteoid osteoma is a painful tumor that most commonly affects the extra-articular parts of the long bones. An intra-articular location of an osteoid osteoma is rare. Various differential diagnoses may arise in connection with such an unusual location because it causes atypical clinical signs.

A rare cause of arthropathy: An ochronotic patient with black joints.

Introduction: Alkaptonuria is an autosomal recessive disorder of metabolism. The pathogenesis of alkaptonuria includes chronic inflammation, degeneration, and eventually osteoarthritis. Ochronotic arthropathy is a rare condition found in patients with alkaptonuria.