X-ray of mortise in a 13-year-old boy with left ankle pain
Lateral x-ray of the patient
A 13-year-old boy presents with pain in his left ankle following a fall 5 days earlier. X-rays taken at an outside urgent care facility show no evidence of fracture. A physical examination reveals pain to palpation over the distal fibula physis consistent with a Salter-Harris type 1 fracture. An incidental bone cyst is noted in the distal tibia, and the patient’s parents would like to know if the lesion requires further treatment.
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The lesion appears benign on x-ray, as the zone of transition between the lesion and adjacent normal bone has a well-defined margin. There is no periosteal reaction or wide zone of transition that would suggest a malignancy. The lesion is also asymptomatic, was found incidentally on x-ray, and occurred in a skeletally immature patient, all of which are typical of benign lesions. Common benign metaphyseal tumors include nonossifying fibroma (NOF) and bone cysts (solitary, aneurysmal, and giant cell).
Characteristic findings of a NOF on x-ray include a sharply demarcated, asymmetrical, lucent lesion with a thin sclerotic rim. NOFs are commonly found in the metaphyseal region adjacent to the physis and migrate to the diaphysis with skeletal growth. X-rays can accurately diagnose NOFs, and magnetic resonance imaging (MRI) is not routinely ordered. Provided that the lesion appears benign and the patient has no associated pain, biopsy is not warranted.
During skeletal maturity, NOFs will progressively ossify and rarely need any treatment or follow-up. In large lesions that occupy more than 50% of the diameter of bone, prophylactic curettage and bone grafting may be indicated to prevent pathologic fracture. In this case, the patient’s parents were advised to have the x-rays repeated after 6 months to ensure that the lesion did not enlarge or change in appearance.
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).
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