Occult fracture of the femoral neck associated with extensive osteonecrosis of the femoral head: A case report.
BACKGROUND
Although the subchondral portion of the femoral head is a common site for collapse in osteonecrosis of the femoral head (ONFH), femoral-neck fracture rarely occurs during the course of ONFH. We report a case of occult insufficiency fracture of the femoral neck without conditions predisposing to insufficiency fractures, occurring in association with ONFH.


METHODS
We report a case of occult fracture of the femoral neck due to extensive ONFH in a 60-year-old man. No abnormal findings suggestive of ONFH were identified on radiographs, and the fracture occurred spontaneously without any trauma or unusual increase in activity. The patient's medical history, age, and good bone quality suggested ONFH as a possible underlying cause. Contrast-enhanced magnetic resonance imaging was useful in determining whether the fracture was caused by ONFH or was instead a simple insufficiency fracture caused by steroid use.


CONCLUSIONS
The patient was treated with bipolar hemiarthroplasty, but if we had not suspected ONFH as a predisposing condition, the undisplaced fracture might have been treated by osteosynthesis, and this would have led to nonunion or collapse of the femoral head. To avoid providing improper treatment, clinicians should consider ONFH as a predisposing factor in pathologic fractures of the femoral neck.


CONCLUSIONS
ONFH should be included in the differential diagnosis of insufficiency fracture of the femoral neck.
Department of Orthopaedic Surgery, Kanazawa Medical University, Kahoku-gun, Japan. Electronic address: 66406kf@kanazawa-med.ac.jp.
Kiyokazu
K
Fukui
Department of Orthopaedic Surgery, Kanazawa Medical University, Kahoku-gun, Japan.
Ayumi
A
Kaneuji
Department of Orthopaedic Surgery, Kanazawa Medical University, Kahoku-gun, Japan.
Tadami
T
Matsumoto
Femoral neck; Occult fracture; Osteonecrosis of the femoral head