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Figure. Anteroposterior radiograph of the left knee. Credit: Dagan Cloutier, MPAS, PA-C
A 19-year-old man presents with left thigh pain and a mass that he reports has been present for the past 2 years. Recently, the patient has been playing more soccer and noticed that his lateral thigh has become sore. On physical examination, a palpable mass is felt near the left side of the distal thigh about 2 inches above the superior pole of the patella. As he bends and straightens his knee, popping sounds are heard and the patient feels the IT band rolling over the mass. Radiography of the knee shows a mass on the lateral distal femur (Figure). Magnetic resonance imaging (MRI) displays a pedunculated osseous protuberance at the metaphysis of the distal lateral left femur with a cartilaginous cap. Mild edema to the vastus medialis muscle is present secondary to mass effect/impingement of the lesion.
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The patient has a lesion at the lateral distal femur consistent with a benign osteochondroma. Osteochondromas are the most common benign bone tumor1 and the majority are asymptomatic and found incidentally on imaging. Malignant transformation of osteochondromas is rare (<1%); therefore, most are left alone. Tumor growth after skeletal maturity raises suspicion of potential malignant transformation.1,2
Radiographs, magnetic resonance imaging (MRI), and clinical presentation are sufficient for an osteochondroma diagnosis and bone biopsy is not indicated. Osteochondromas rarely cause a mass effect on surrounding nerves, blood vessels, muscles, tendons, and other soft tissue. 1,2
Surgical resection of the osteochondroma is the treatment of choice in symptomatic patients when conservative treatments fail. Resection is considered a curative surgery as less than 2% of osteochondromas will reoccur. Resection should be performed after the patient reaches skeletal maturity to be sure no further growth occurs.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.
References
1. Heron N. Femoral exostosis causing vastus medialis pain in an active young lady: a case report. BMC Res Notes. 2015;8:119. doi:10.1186/s13104-015-1077-0
2. Wodajo FM. Top five lesions that do not need referral to orthopedic oncology. Orthop Clin North Am. 2015;46(2):303-314. doi:10.1016/j.ocl.2014.11.012
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