Unicameral bone cysts: Current concepts.

Unicameral bone cysts (UBC) or simple/solitary bone cysts are benign fluid filled cavities that enlarge over time, resulting in thinning of the bone. Usually these cysts are reported in the metaphyseal areas of long bones with open physes. 85% of UBCs occur almost exclusively in children and adolescents. UBCs are more aggressive in the first decade of life and correspondingly the recurrence rate for these patients is four times that for adolescents. The proximal humerus and femur account for almost 90% of these cases. UBCs are classified as active when they are within 1 cm of the physis and latent as they progress to a diaphyseal location. Differential diagnoses for UBC include aneurysmal bone cyst, fibrous dysplasia, enchondroma, and intraosseous ganglia. By the time of skeletal maturity most UBCs tend to resolve. Nonoperative treatment may be a viable option for many patients with small or symptomatic lesions. Interventions include steroid injection, open curettage and bone grafting, decompression and percutaneous injection of marrow or graft substitutes.