What is a unicameral bone cyst? A unicameral bone cyst, otherwise known as a simple bone cyst, is a fluid-filled cavity in the bone, lined by compressed fibrous tissue. It usually occurs in the long bones of a growing child, especially the upper part of the humerus (50 - 60% of the time) or the upper part of the femur (25-30 % of the time). Other bones, however, can be affected. Boston Children's Hospital Expert

Description A unicameral (simple) bone cyst is a cavity found within a bone that is filled with straw colored fluid. It is a benign condition (non-cancerous). Unicameral bone cysts (UBC) are usually found in patients younger than 20 years of age. UBCs occur in one bone, in one location. The location of the cysts tends to be in the upper arm (proximal humerus) or thighbone (proximal femur). Less common locations include the pelvis, ankle (talus) or heel (calcaneus). AAOS Patient Information