A 12-year-old boy presents to the office with pain in his right knee that has persisted for 4 months. He describes the pain as throbbing at the medial knee, and the pain is worse with running. Bending the knee is particularly painful. Anteroposterior radiograph of the right femur (Figure) reveals a bony outgrowth on the medial side of the distal femur.
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The patient’s imaging results are consistent with an osteochondroma, a common benign bone tumor that develops near the surface of a growth plate during adolescence. Most osteochondromas are asymptomatic and found incidentally on radiography. Osteochondromas are made of bone and cartilage, and can continue to grow until the patient reaches skeletal maturity. In this case, the large osteochondroma is likely causing a mass effect on the medial soft tissues, resulting in knee pain and dysfunction.
The tumor in this case is a pedunculated osteochondroma, which is formed from a stalk that sticks out from normal bone. The diagnosis of an osteochondroma is often made based on radiographic findings alone, but magnetic resonance imaging can help measure the cartilaginous cap on osteochondromas and help rule out malignant transformation. For a solitary osteochondroma, there is a 1% chance of the benign tumor transforming to a malignancy.1
Indications for surgical excision include pain and mechanical impingement of the tumor on soft tissues. Surgical treatment involves marginal excision of the tumor from the base of the stalk to the cartilaginous cap. The reoccurrence rate after surgical excision is <5%.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
1. August Image Quiz: Osteochondroma. JB JS Open Access. 2015;3(3):16-17.
2. McKean J, O’Donnell P. Osteochondroma & multiple hereditary exostosis. OrthoBullets website. https://www.orthobullets.com/pathology/8020/osteochondroma-and-multiple-hereditary-exostosis. Updated December 8, 2019. Accessed December 11, 2019.