Osteochondroma

During a follow-up visit for type 2 diabetes mellitus, a 29-year-old man mentioned that he had left hip pain. Results of a musculoskeletal examination were normal except for a hard, nonmobile, nontender mass on the left medial proximal tibia (A). A radiograph showed a large exostosis projecting from the medial aspect of the proximal tibia (B).

Osteochondroma was diagnosed; this developmental dysplasia of peripheral growth plate forms a cartilage-capped projection of bone. It usually occurs at the metaphyses of long bones.The most common sites are the proximal or distal femur, proximal humerus, proximal tibia, pelvis, and scapula.

Osteochondromas are benign, slow-growing tumors that continue to enlarge during skeletal growth but rarely enlarge after childhood. They comprise at least 45% of benign bone tumors. The risk of sarcomatous transformation in a solitary exostosis is about 1%; however, in patients with multiple hereditary exostoses, approximately 10% undergo sarcomatous transformation.

Radiologic examination shows a flat, sessile, or pedunculated process. Pedunculated osteochondromas are in the proximal direction. The tumor blends into the underlying metaphysis. Calcification may be seen in the cartilaginous cap and increases with age.

No treatment is necessary if the patient is asymptomatic. Surgical resection is done if the tumor continues to grow after skeletal maturity and if malignancy is suspected. Also surgery is indicated if the patient has persistent pain or neurovascular compromise. Recurrence following excision of a solitary exostosis is less than 5%.

This patient was referred to an orthopedist for further evaluation. Because the patient was asymptomatic, he did not need any further workup and his exostosis was to be monitored.