Male with ankle pain. A radiolucent lesion having geographic sclerotic margins with mild cortical thinning and mild osseous expansion of the body of the right calcaneus. A simple bone cyst is a common lesion of unknown cause and pathogenesis. On macroscopic examination, the cyst usually, but not invariably, contains fluid. A membrane generally lines the cystic cavity.
Fracture represents a significant sequela of simple bone cysts.
These fractures may be accompanied by a vertical fragment within the cyst , a finding which has been designated as the fallen fragment sign. Fibrous septa may form after fracture. Simple bone cysts generally occur in the first and second decades of life and affect boys more than girls. In patients below the age of 20 years, cysts generally are observed in the tubular bones, particularly the proximal end of the humerus. In patients older than 20, they tend to occur more frequently in the innominate bone the calcaneus.