Review Question - QID 5847

This patient presents with a non-displaced pathologic fracture through a unicameral bone cyst (UBC) of the right proximal humerus. The best next step would be a sling for comfort.

Unicameral bone cysts are non-neoplastic, serous fluid-filled bone lesions that are thought to result from temporary failure of medullary bone formation near the physis. They are most commonly located in the proximal humerus. A pathologic fracture may be the first known presentation of the cyst, as these lesions are usually asymptomatic.

Pretell-Mazzini et al. reviewed unicameral bone cysts. These benign lesions occur almost exclusively in children and adolescents (up to 85% of cases) with a reported peak between ages 3 and 14 years. Primary differential diagnoses for UBC include aneurysmal bone cyst (ABC), fibrous dysplasia, enchondroma, and intraosseous ganglia. In patients with a pathologic fracture of the upper extremity associated with a UBC, initial nonsurgical treatment with immobilization for 4 to 6 weeks is appropriate.

Donaldson et al. evaluated whether simple bone cysts (SBC) resolve with age. Twenty-four patients were followed for 7.0 ± 1.0 years following initial treatment with a mean age at follow-up of 17.2 ± 3.2 years. Despite the assumption that most simple bone cysts will resolve with skeletal maturity, none of the cysts were graded as completely healed in this study. They concluded that growth plate closure may not signify healing of simple bone cysts.

Figure A is an AP radiograph of the right shoulder showing a undisplaced right humeral unicameral bone cyst, pathologic fracture. It demonstrates typical findings of a bone cyst, i.e. central metaphyseal lucency, close to or abutting the growth plate, with uniform cortical thinning and no matrix production.

Incorrect Answers:
Answers 1-3: Simple bone cysts do not require pathological workup.
Answer 4: As noted above, patients with a pathologic fracture of the upper extremity associated with a UBC, initial nonsurgical treatment with immobilization for 4 to 6 weeks is appropriate. In patients with intact and isolated lesions, curettage and bone grafting has been the definitive open procedure for management of UBC. However, innovative techniques have been described recently, including decompression (with no instrumentation left in place), instrumentation (eg, cannulated screws, flexible intramedullary nails), and/or combined methods.