Review Question - QID 2084

Figure A is a radiograph demonstrating the "fallen leaf sign." The patient has a pathologic fracture through unicameral bone cyst (UBC), which is treated definitively with immobilization.

UBCs or solitary bone cysts are unusual tumors seen in the ends of long bones in skeletally immature children. They usually present with pathologic fractures through thin, weakened bone. They are usually minimally displaced. A fragment of the cyst wall may fall into the fluid and may be evidenced by the "fallen leaf sign." Fractures are usually metaphyseal and rarely involve the epiphysis. Initial treatment is non-operative and involves immobilization.

Wilkins performed a review of UBCs. He reports that if cysts are fractured, they may undergo an involutional process and heal. If an initial period of immobilization is performed, internal fixation can usually be avoided. The exception is when the fracture is located in a high-stress weight-bearing area, such as the femur.

Sung et al. performed a retrospective study examining the efficacy of three surgical treatments of UBCs. They compared injection of corticosteroids, curettage plus bone grafting, or a combination injection of steroids, demineralized bone matrix, and bone marrow aspirate. They found that curettage was associated with the lowest rate of posttreatment pathologic fractures, but the highest rate of pain and other complications. They conclude that combination injection is a reasonable first treatment for UBC, as it is less invasive but comparable to curettage in preventing recurrence.

Figure A is an AP radiograph of the right shoulder demonstrating a proximal humerus fracture through a UBC. Illustration A is the same image with an arrow demonstrating the fallen leaf sign.

Incorrect Answers:
Answer 2: MRI is not necessary when treating a fracture through a UBC. The radiographs are characteristic for this lesion.
Answers 3, 4, & 5: The initial treatment of a fracture through a UBC is conservative. If the fracture occurs through a weight-bearing bone, operative stabilization is indicated.