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Findings: AP pelvis and bilateral plain film views of the hips demonstrate generalized osteopenia. Linear areas of inhomogeneous trabecular sclerosis involving bilateral subcapital femoral necks is present. Comparison view of the pelvis six months prior (which is not included) showed normal hips.

Technetium 99m MDP bone scan: Increased radiotracer uptake within bilateral femoral necks.

Diagnosis: Insufficiency stress fractures of bilateral femoral necks.

Discussion: Stress fractures are categorized as fatigue or insufficiency fractures. Fatigue fractures are a result of abnormal stress on normal bone with normal elastic resistance. Insufficiency fractures result from normal physiologic stress placed on abnormal bone with deficient elastic resistance.

Insufficiency type stress fractures may appear in elderly patients with osteoporosis. The most common sites of involvement include the sacrum, pubis, and lower extremities. Other contributing factors include rheumatoid arthritis, steroid therapy, Paget's, osteomalacia, hyperparathyroidism, and osteogenisis imperfecta.

Early findings may be absent. "Scintigraphy with technetium 99m phosphate compounds has detected up to 60% early stress fractures before the appearance of radiographic signs" (2). This is manifest by focal areas of increased uptake.

Early diagnosis of femoral neck stress fractures is important. Delayed diagnosis can result in fracture/displacement, deformity, nonunion and avascular necrosis. Therefore, if there is high clinical suspicion, but negative x-ray and bone scan, repeat studies in one to two weeks is warranted.

References:
1. Resnick: Bone and Joint Imaging, 1989. pp 189-192, 586-587.

2. Dorne L, Lander PH: Spontaneous Stress Fractures of the Femoral Neck AJR ,1985. 144:343-347.

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