Unicameral bone cyst with epiphyseal involvement: clinicoanatomic analysis.

Epiphyseal involvement of a unicameral bone cyst (UBC) is rare. This anatomic setting represents a distinct clinical and radiographic entity. This study reports a new case and analyzes the clinical and biological behavior of seven additional UBCs with epiphyseal involvement from the literature. We report the first successful treatment of this variant with methylprednisolone acetate. The average age was 20.1 years with a male to female ratio of 1.3:1. Anatomic location: proximal femur (4), proximal humerus (2), and proximal tibia (2). Both age and location were atypical when compared to the classic metaphyseal location. Radiographically, all lesions presented a characteristic involvement of the epiphysis and metaphysis in various proportions. The epiphyseal plates were judged closed versus open in 50%, respectively. Follow-up ranged from 9 months to 3 years. Six cases healed following a single curettage (three with and three without bone graft). There were no late complications of fracture, deformity, shortening, or avascular necrosis. Recurrence was 0%. No secondary procedures were required. We conclude the age, location, and radiographic appearance is atypical and diagnosis is difficult, but the biological behavior is less aggressive and the prognosis more favorable than the typical, metaphyseal UBC. Curettage with or without bone graft has a high success rate. We recommend aspiration and intralesional methylprednisolone as the initial management. We hypothesize that epiphyseal UBCs have a better prognosis than metaphyseal location alone due to the older age, atypical location, and the potential of the epiphysis to reossify.