Femoral Neck Fracture with Avascular Necrosis

DISCUSSION

Dual-energy x-ray absorptiometry is recommended for women aged 65 y or older to screen for osteopenia and osteoporosis (1). The goal of screening is to identify those at increased risk of an insufficiency fracture due to a low bone mass. Screening typically evaluates the hip and lumbar spine and, occasionally, the forearm. The World Health Organization has devised the Fracture Risk Assessment Tool to estimate the risk that a patient will sustain a major osteoporotic fracture or hip fracture, based, in part, on bone mineral density (2).

Hip fractures are problematic, particularly in the elderly, with complications such as avascular necrosis of the femoral head. In one study, the incidence of avascular necrosis in patients with femoral neck fractures was 14.3% (3). MRI is the gold standard for evaluating avascular necrosis (4). However, bone scintigraphy is an option. Expected findings on MRI are hypointensity on T1-weighted images, sometimes bordered by a hyperintense line. T2-weighted images may show the double-line sign, consisting of a hyperintense inner line between normal marrow and ischemic marrow. On bone scintigraphy, early avascular necrosis shows photopenia on all phases because of absence of blood flow. Late avascular necrosis shows increased bone tracer activity due to reparative uptake.