In some old fractures, cailaginous tissue forms over the fractured bone ends with a cavity in between containing clear fluid. This condition is known as:

Pseudahrosis is a false joint that may develop after a fracture that has not united properly due to inadequate immobilization. Inadequate immobilization permits constant movements at the fracture site so that the normal constituents of callus do not form consequently the callus may be composed mainly of fibrous tissue cailage, perpetuating the instability and resulting in delayed union or nonunion. If a non union allows for too much motion along the fracture gap, the central poion of the callus undergoes cystic degeneration and luminal surface can actually become lined by synol like cells, creating a false joint filled with clear fluid. This is known as pseudahrosis. Ref: Robbin's Pathologic basis of Disease 7/e, Page 1289; Apley's system of Ohopedics & fractures 8/e, Page 156,164,544 ; Natarajan's ohopedics , Page 27; Murcer's Ohopedic surgery 9/e, Page 433, 811, 1095, 672,736.