Causes / typical injury mechanism: Sacral fractures are relatively common pelvic ring injuries that may occur following trauma to the region. Common causes of sacral fractures include motor vehicle crashes, falls from a height, and minor trauma in patients with osteoporosis.

Classic history and presentation: Sacral fractures present with a broad range of severity, depending on the amount of energy applied to the patient at the time of injury. Sacral fractures may be associated with neurovascular compromise depending on the location of the fracture and the degree of displacement. Patients will typically present with pain and soft tissue trauma around the pelvis.

Prevalence: The prevalence of nonosteoporotic sacral fractures in adults is estimated to be approximately 2.1 cases per 100 000 people. At-risk older patients with osteoporosis have an estimated incidence of sacral fractures of 1%-5%.

• Age – Can occur at any age but is more prevalent in older patients (especially patients with osteoporosis).
• Sex / gender – There are no known differences in sacral fracture prevalence due to sex.

Risk factors: The primary known risk factors for sacral fractures are older age, conditions that lead to falls, and osteoporosis. Similarly, sacral insufficiency fractures are more likely to occur in patients with underlying metabolic bone disease, such as osteoporosis or Paget disease.

Pathophysiology: In young and healthy individuals, sacral fractures are most commonly due to high-energy trauma. In older patients with underlying metabolic bone disease and conditions that lead to falls, sacral fractures may result from lower energy trauma or sacral insufficiency fractures may occur (due to underlying frailty or secondary to radiation).

S1-S4 nerve roots exit through the sacral foramina. S2-S5 nerve roots control bowel, bladder, and sexual function. Displaced fractures can compromise these nerves.

Grade / classification system: The most common method of classification is the Denis classification system, which divides the sacrum into 3 distinct zones to classify longitudinal fractures:

• Zone 1 – Fractures lateral to the foramina (including the sacral ala)
• Lowest risk of neurologic injury (6%) and the most common location for low-energy fractures
• Zone 2 – Fractures that traverse the foramina
• Associated with possible hemodynamic instability due to potential damage to the sacral arteries as well as potential neurologic injury (28%)
• Zone 3 – Fractures medial to the foramina (including the sacral canal)
• Highest risk of neurologic injury (56%) and potential cauda equina syndrome

Additional types of sacral fractures include:

• Transverse sacral fractures (Roy-Camille classification) – typically considered to affect Zone III and are associated with a high risk of neurologic injury.
• U-shaped fractures – combined longitudinal and transverse fractures that are associated with spino-pelvic dissociation and have a high risk of neurologic injury.