Unicameral Bone Cyst With Atypical Location In Distal Femur : A Case Report

Abstract

Unicameral bone cysts (UBCs) are benign fluid-containing cavities commonly found in the proximal humerus and femur. However, their rare occurrence in atypical location like the distal femur requires further evaluation. We present the case of a six-year-old boy with pathological fracture of the distal femur following a trivial injury. Radiographic imaging revealed a centrally located lytic lesion with ‘fallen fragment’ sign, otherwise no mass seen within the cyst. Atypical location raised concerns about other possible differentials such as aneurysmal bone cyst, eosinophilic granuloma, fibrous dysplasia or telangiectatic osteosarcoma. We utilized intraoperative frozen section to rule out malignancy before proceeding with surgical curettage, bone grafting and plate stabilization. The final histopathological result confirmed the UBC. Imaging during follow-up showed evidence of cyst and fracture healing. At one-year, the patient had achieved full function with no cyst recurrence. Further evaluation would be necessary to confirm the diagnosis of UBCs if found in atypical locations. Intraoperative frozen section is valuable diagnostic and therapeutic tool.