Avascular necrosis of the femoral head following an occult femoral neck stress fracture

Introduction. Osteonecrosis (ON) of the femoral head (FH) - (ONFH) is an intractable disease that causes progressive femoral head collapse, severe pain, and gait disturbance. We report a case of avascular necrosis of the femoral head following an occult femoral neck (FN) stress fracture. Case report. A 55-year-old woman presented to our department with a chief complaint of low back pain that radiated into the left anterolateral thigh over the period of two months. Her left anterolateral thigh became progressively more painful over the past two weeks. No abnormal findings indicative of ONFH or an occult fracture of the FN were detected by X-ray or computed tomography, but an occult insufficiency fracture of the left FN was identified on magnetic resonance imaging (MRI). The diagnosis of FN stress fracture was delayed, resulting in femoral head necrosis. The fracture was treated with total hip arthroplasty, and the resected FH was subjected to histopathology (HP). Based on the HP findings, the final diagnosis of this case was ONFH with an occult fracture of the left FN. Clinical symptoms were relieved postoperatively. Conclusion. An early MRI examination is recommended in patients presenting with a suspected stress fracture of the FN to avoid FH necrosis due to a delayed diagnosis.