Fallen fragment sign and hinged faragemnt sing are signs of simple bone cyst SIMPLE BONY CYST : ACTIVE : Develop in patients under 10 years of age * Cyst arises adjacent to growth plate & may grow to fill most of metaphysis Bone may be slightly expanded within coical shell * May cause pathologic fracture PASSIVE : Passive cysts patients are usually over 12 years of age &; become increasingly separated from gmwth plate (more ) than 1-2 an) have thicker bony wall than active lesions may show evidence of healing or ossification less likely to result in fracture CAUSES : * The cause of a unicameral bone cyst remains unknown. Theories have been proposed but none have been definitively proven. * One of these theories is that the cysts result from a disorder of the growth plate. * Another is that the cysts result from problems with circulation that are caused by a developmental anomaly in the veins of the affected bone. * The role trauma plays in the development of these cysts is unknown. Symptoms: * Unless there has been a fracture, bone cysts arc without symptoms. * They may occasionally be discovered by chance on x-rays obtained for other reasons. * There is no mass or tenderness unless there is a fracture. * There may be an abnormal angulation of the limb secondary to the fracture or shoening of the limb if the adjacent growth plate is involved. Location lesion appears to arise from the growth plate & in early stages, lesion is lies adjacent to growth plate; typically the simple bone cyst will have a central location, whereas an ABC will have a slightly eccentric location; predilection for the metaphysis of long bones; - proximal humerus (SO% of cases) - proximal tibia - proximal femur (40%) - foot:Calcaneal Bone Cysts Radiographs show a central, well marginated & symmetric radiolucent defect in metaphysis metaphyseal bone does not remodel normally metaphysis is broader than normally seen but not broader than with width of epiphyseal plate thin rim of non reative bone borders the unicameral bone cyst Refer textbook of musculoskeletal tumor p 112