Atypical Presentation of Navicular Aneurysmal Bone Cyst in a Symptomatic Pediatric Flatfoot Deformity: A Case Report.

Aneurysmal bone cysts (ABCs) are rare in the foot, accounting for 4% to 6.3% of all ABCs found in the body. Approximately 80% of patients diagnosed with an ABC are in the second decade of life. While benign, pain and deformity are often the presenting symptoms. This report's objective is to describe, to our knowledge, the first reported case of a pediatric navicular ABC in association with pediatric flatfoot deformity that was successfully treated with curettage and bone grafting. An additional goal of the report is to highlight how the diagnosis of these osseous tumors can easily be missed given the overlap in symptoms with pediatric flatfoot deformity. An 11-year-old female presented to clinic with a chief complaint of painful, flatfoot deformity and discomfort to the medial midfoot after walking for more than 2 city blocks. The patient was conservatively treated for pediatric flatfoot deformity at an outside institution and advised that a surgical flatfoot reconstruction would be necessary to relieve her symptomology. On examination, the patient exhibited focal pain to the medial aspect of the navicular. Radiographs revealed an ill-defined, expansile, sclerotic lesion of the navicular, and MRI demonstrated a multicystic lesion filling the navicular, consistent with an ABC. Treatment included curettage and packing with allograft. At 1-year follow-up, the patient is well, with minimal pain and return to full activity without functional limitations. Local recurrence of an aneurysmal bone cyst following curettage and bone grafting is as high as 22% with patient age and lesion size comprising the main risk factors. This report demonstrates successful curettage of an ABC within the navicular and preservation of osseous articulations in a pediatric patient. At 1-year follow-up, the patient had minimal pain with no evidence of recurrence.

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