Clinical and imaging features of a subchondral insufficiency fracture of the femoral head after internal fixation of a femoral neck fracture: a comparison with those of post-traumatic osteonecrosis of the femoral head

Objective: Recent articles have demonstrated that subchondral insufficiency fractures (SIFs) of the femoral head can occur following internal fixation of femoral neck fractures (FNFs), in addition to post-traumatic osteonecrosis (ON) of the femoral head. The purpose of this study was to determine the clinical and imaging features of SIF after internal fixation of FNFs compared with those of post-traumatic ON. Methods: We reviewed five hips in five patients, who received internal fixation for the treatment of FNF and were diagnosed as having SIF according to the shape of the low-intensity band on the T-1 weighted MR image. Four hips of four patients with post-traumatic ON were compared with the SIF cases. Both the clinical and imaging findings were investigated. Results: There were no significant differences in the age, sex, body mass index, stage of FNF or duration from injury to surgery between SIF and post-traumatic ON. Regarding the prognosis, one of the five cases (20%) with SIF underwent prosthetic replacement owing to a progressive collapse of the femoral head. Two of the four cases (50%) with post-traumatic ON underwent prosthetic replacement. Conclusion: The results of this study suggest that SIF should be considered a possible condition following the internal fixation of FNFs, and it is important to differentiate SIF from post-traumatic ON. Advances in knowledge: SIF should be considered a possible condition following the internal fixation of FNFs.