Subchondral insufficiency fracture of the femoral head: a report of two cases with a history of internal fixation of a femoral neck fracture.

We report our experience in two cases of subchondral insufficiency fracture of the femoral head with a history of internal fixation of the femoral neck fracture. Both cases were young females (26 and 43 years old, respectively). Their hip pain occurred more than 2 years and 1 year after the primary surgical treatment, respectively. MRI revealed bone marrow edema pattern, as well as a low-intensity band on the T1-weighted images, which are commonly observed in osteonecrosis. However, the low-intensity bands were parallel to the subchondral bone end-plate, which are characteristic findings of subchondral insufficiency fracture. Both patients were administered anti-inflammatory drugs and/or bisphosphonate. One patient underwent a transtrochanteric curved varus osteotomy 1 year and 9 months after the onset, and the other healed without collapse of the femoral head. Our cases indicate that subchondral insufficiency fractures may need to be considered as one of the possible conditions after the internal fixation of a femoral neck fracture, in addition to posttraumatic osteonecrosis.