Imaging description

Insufficiency fractures occur when bone strength is not sufficient to withstand physiologic stress. The most common bones fractured are the thoracic and lumbar vertebral bodies. Sacral insufficiency fractures (SIF) are less common but they are commonly misdiagnosed [1]. The typical SIF is an H-shaped tri-part fracture with two vertical components through the sacral alae and a third horizontal component connecting them, usually through the upper sacral segments. Any permutation of these can be seen in a given patient, although isolated transverse component is rare.

Plain films are often non-diagnostic. CT is reliable, although in the acute phase findings may be very subtle secondary to decreased background bone density. MRI is very sensitive and shows the marrow edema associated with the fracture as increased signal on fluid-sensitive pulse sequences such as STIR and SE T2 and diminished signal on T1-weighted images in the bone surrounding the fracture (Figs. 89.1, 89.2). Contrast enhancement occurs in areas of edema. Bone scan is very sensitive but less specific than MRI and CT.