The sacrum is formed by the fusion of 5 sacral vertebrae and articulates with 5th lumbar vertebra proximally and coccyx distally, and with ilia at sacroiliac joints bilaterally. It contains 4 foramina which transmit sacral nerves (L5-S5), which are responsible for the functions of anal sphincter tone / voluntary contracture, bulbocavernosus reflex and perianal sensation. As an osseous structure, sacrum transmits the load distributed by the first sacral segment through iliac wings to the acetabulum.
Sacral fractures are quite common, occurring in up to 45% of pelvic ring injuries related to high energy trauma (in young adults) or low energy falls (in elderly). They are often underdiagnosed and as a consequence, they are frequently mistreated and lead to serious complications such as neural damage (25% of all cases).
The presence of a neurologic deficit is the most single most important factor in predicting the outcome. Untreated fractures with neurologic deficits lead to symptoms of lower extremity motor/sensory deficits and/or urinary/rectal/sexual dysfunction.
Sacral fractures are classified according to the Denis classification. Zone 1 fractures (50% of all) are lateral to the foramina and are least related to a nerve injury. Zone 2 fractures are through foramina, and based on whether they are stable or unstable, have an increased risk of nonunion, nerve damage and poor functional outcome. Fractures that are medial to foramina are associated with the highest rate of neurological deficit (60%), such as bowel, bladder, and sexual dysfunction. Transverse sacral fractures also have a high incidence of nerve dysfunction. The u-type sacral fractures result from axial loading and represent spino-pelvic dissociation; these too have a high incidence of neurologic complications.
The clinical diagnosis begins with taking a proper history – motor vehicle accident or fall from height are the most common causes of these fractures, but repetitive stress, insufficiency fracture in osteoporotic adults are also important predisposing factors. The most prominent symptom is peripelvic pain. The physical exam should include testing for pelvic ring stability by internally and externally rotating iliac wings, palpating for subcutaneous fluid mass indicative of lumbosacral fascial degloving, as well as performing a vaginal exam in women to rule-out open injury. A focused neurologic, vascular and rectal exams are also important to assess the degree of tissue damage.
Radiographs are required to diagnose a sacral fracture, although only 30% show sacral fractures. CT is by far the diagnostic study of choice for proper assessment of the fracture, while MRI is considered when neural compromise is suspected.
Nonoperative management includes progressive weight bearing with orthosis if needed, and can only be considered in patients with <1 cm displacement and no neurologic deficit, and in cases of insufficiency fractures. Surgical fixation (without decompression) should be considered if there is a displaced fracture >1 cm with associated soft tissue compromise and persistent pain after non-operative management, and also if there is displacement of fracture after non-operative management. Surgical fixation with decompression is the treatment of choice whenever there is evidence for neurologic injury.