Teaching Case

A 30-years old neurologist felt walking down the stairs, landing on buttocks. During the physical examination, the emergency department physician noticed mild perianal hypoesthesia.

CT and MRI were obtained for diagnosis. Sagittal bone window CT of the pelvis (figure 1) demonstrates a transverse fracture through the S4 vertebral body and posterior elements (white arrow), with a mild retrolisthesis of the upper fragment.

MR sagittal T1W and T2W (figures 2a and 2c), and oblique coronal T1W and T2W (figure 2b and 2d) Dixon images of the pelvis show cancellous bone marrow oedema (white asterisk) associated with the fracture previously described (white arrows). Discrete sacral canal stenosis is noticed.

Transverse sacral fractures [TSF} are uncommon. They constitute up to 5% of sacral fractures, and they usually occur in young adults. A fall landing on the buttocks causes 35% of them, with 37% caused by motor vehicle accidents.

TSF can be categorized in high and low fractures, with both having a horizontal plane separation and two sacral fragments. The Denis classification of sacral fractures includes them in the zone III fractures. Nevertheless, many transverse sacral fractures affect the three zones described. They were later classified into four categories by Camille et al., but only including transverse high sacral fractures. They can be associated with thoracolumbar burst fractures.

High transverse sacral fractures are more common than low transverse sacral fractures. They are usually secondary to a high-energy traumatic event due to Indirect forces coming from the pelvis and lumbar spine and fixed to the sacrum.

Low transverse sacral fractures are mainly due to a direct impact against the coccyx or a direct hit to the lower sacral segments. The mechanism involved is a levering action through the distal sacrum, below the sacroiliac joints' level of fixation. Any of the three last sacral vertebrae may be affected. They are usually stable fractures.

A sacral fracture should always be suspected after trauma with resulting sacrococcygeal pain or a pelvic ring fracture with neurological deficits.

TSF is more often associated with neurological deficits than vertical fractures. The most commonly described neurological deficits are bowel-bladder dysfunction and saddle anaesthesia. A sacral root injury could produce sexual impairment [1].

In general, sacral fractures may be hard to identify on conventional radiology due to the overlying bowel gas, the bladder silhouette, and the normal angulation of the sacrum. TSF fractures are best seen in a lateral sacrum view, although an anteroposterior radiograph could show a step ladder by displacement and overriding of the sacral fragments.

CT and MRI have a higher sensitivity for transverse sacral fractures than conventional radiology. Besides the sacral horizontal fracture, cancellous bone marrow oedema, and paravertebral soft tissue oedema may be seen [2]. It is essential to describe if there is any displacement of the sacral fragments and sacral canal stenosis.

Management and treatment will depend on the patient's neurological status and the stability of the fracture. A fracture displacement of 1 cm or more is considered to be unstable. Low transverse sacral fractures usually don't need to be stabilized [1].

Written informed patient consent for publication has been obtained.'