Trauma-Induced Resolution of Solitary Osteochondroma of the Distal Femur.

Osteochondromas are benign lesions manifested as bony protrusions capped by cartilage. The exact cause of these growths is not known, and there is no treatment other than surgical excision if the lesion becomes symptomatic. Spontaneous resolution is an uncommon phenomenon that is not completely understood. A 12-year-old girl presented with a mass behind the left knee diagnosed as an osteochondroma. She was followed with serial radiographs because the lesion was minimally symptomatic. At 2.5 years after presentation, the patient reported feeling a "pop" with knee hyperflexion, and radiographic follow-up confirmed a decrease in the size of the growth. The protrusion continued to decrease in size until it was no longer detectable with radiographs, physical examination, and advanced imaging. Spontaneously resolving osteochondromas have been previously documented, but the literature is limited. There were just over 20 cases reported as of the writing of this article, and only 1 other case includes postresolution magnetic resonance imaging. This report of localized trauma inducing spontaneous resolution provides additional evidence and insight supporting previous theories on spontaneous resolution of osteochondromas, which may assist in counseling patients and their families regarding expected natural history. [Orthopedics.2016; 39(5):e1001-e1004.].