Plain X rays for Osteonecrosis
What is the role of plain radiographs in the diagnosis of Osteonecrosis?
Initially, plain films are normal. Later, a region of generalized osteopenia may develop (a nonspecific finding). Eventually, after bone repair mechanisms have had time to work, a mottled appearance develops in the affected area because of the presence of “cysts” (regions of dead bone resorption) and contiguous sclerosis (regions of bone repair).
Early collapse of the cancellous bone beneath the subchondral plate is apparent as a pathognomonic radiolucent line frequently referred to as the crescent sign. Once in this stage, further collapse is almost inevitable, thus, it represents the earliest irreversible lesion of ON. Once the articular surface has collapsed and flattened, secondary degenerative changes develop, resulting in joint space narrowing and secondary involvement of other bones within the articulation (e.g., acetabulum).
