Review Question - QID 1523

The clinical presentation and radiograph are consistent with a pathologic fracture through a likely unicameral bone cyst. Appropriate initial management includes immobilization in a sling until the fracture has healed. Since the lesion is benign in appearance, biopsy is not indicated at this time.

Unicameral bone cysts (UBC), or simple cysts, are serous fluid-filled bone lesions usually found in patients younger than 20 years of age. Radiographically, they present as central, lytic lesions that rarely cross the physis. Approximately 50-75% of patients with a UBC present with a pathological fracture. Initial treatment focuses on immobilizing the fracture with a sling for 4-6 weeks. Once the fracture is healed, intervention should be considered for those lesions that remain symptomatic, active (abutting the growth plate), or have increased in size. Options for intervention include injection with steroid or bone marrow, curettage and bone grafting, and internal fixation.

Rougraff et al treated 23 patients with "active" unicameral bone cysts with trephination and injection of allogeneic demineralized bone matrix and autogenous bone marrow. They found pain relief and prevention of pathologic fracture in 78% of patients after one injection, and 100% of patients after two injections. They conclude that percutaneous injection of a combination of allogeneic demineralized bone matrix and autogenous bone marrow is an effective treatment for active unicameral bone cysts.

Roposch et al treated 32 patients with unicameral bone cysts in either the proximal humerus, proximal femur, or distal radius with flexible intramedullary nailing. 30 of these patients had already sustained a pathological fracture. 30 of the 32 lesions had healed within 36 months. They conclude that flexible IM nailing is an effective treatment for unicameral bone cysts in long bones.

Figure A shows a central, well marginated, radiolucent defect in the metaphysis of the proximal humerus with associated pathologic fracture. Illustration A shows another example of a pathologic fracture through a unicameral bone cyst with the arrow pointing to the "fallen leaf" sign. This is caused by the cortical fracture fragment displacing centrally into the fluid-filled cyst.

Incorrect Answers:
Answer 1: Aspiration and injection of steroid may be indicated when the fracture has healed, but is not the appropriate initial management for a UBC with a pathologic fracture.
Answer 2: Internal fixation is considered if conservative management fails.
Answer 3: Given the benign appearance of the lesion, radiation and chemotherapy are not indicated.
Answer 5: Radiofrequency ablation is the appropriate management for osteoid osteoma, not a pathologic fracture through a UBC.