The sacrum is a large, triangular bone situated at the base of the spine, composed of five fused vertebrae. It provides a stable foundation for the spinal column and transfers the upper body’s weight to the legs. A fall is a frequent mechanism of injury, especially in older individuals whose bone density may be compromised by osteoporosis. Because the sacrum houses nerve roots controlling leg function and pelvic organs, a fracture in this area carries a high risk of neurological damage.
Identifying the Injury
Following a fall, the most common symptom of a sacral fracture is severe, localized pain in the lower back, buttocks, or hip region. This deep, persistent pain is intensified by any movement, including shifting position, sitting, or standing, as the activity places pressure on the fractured bone. Unlike a simple muscle strain, the pain may not improve with rest or over-the-counter pain relievers. Visible bruising and swelling may also be observed around the tailbone or gluteal area.
The most concerning signs involve the nervous system, as the fracture may be pressing on or damaging the sacral nerve roots. These neurological “red flags” demand immediate medical attention, signaling a potentially unstable injury. Symptoms can include numbness, tingling, or a burning sensation that radiates down the legs or into the feet. Weakness in the lower extremities, sometimes causing a noticeable change in gait, is another serious indicator of nerve involvement.
A particularly concerning cluster of symptoms involves changes in bowel or bladder function, such as difficulty controlling urination or bowel movements, which may indicate cauda equina syndrome. This loss of control, along with perianal numbness, signifies a high-risk injury extending into the central spinal canal. Anyone experiencing these specific neurological deficits after a fall must seek emergency medical evaluation without delay.
How Doctors Classify the Fracture
The diagnostic process begins with standard X-rays, though these are often insufficient because the sacrum’s complex shape and overlap with other pelvic bones can obscure fracture lines. Due to this challenge, a Computed Tomography (CT) scan is the standard imaging technique for visualizing the bony architecture and fracture pattern. A CT scan is crucial for determining the precise extent of the bone injury and the degree of displacement.
Magnetic Resonance Imaging (MRI) is utilized when a stress fracture is suspected or when neurological symptoms are present, as it provides the clearest picture of soft tissues and nerve structures. The findings from these imaging studies allow doctors to classify the fracture, which dictates the subsequent treatment plan. One common system, the Denis classification, divides the sacrum into three zones based on the fracture line’s location relative to the nerve passageways (foramina).
A Zone I fracture is lateral to the foramina and has the lowest risk of nerve injury, while a Zone III fracture extends into the central spinal canal and carries the highest risk of severe neurological issues. The distinction between a stable and an unstable fracture is the most important classification. Stable fractures are non-displaced and do not compromise the pelvic ring’s integrity. Unstable fractures involve significant displacement or damage to the ligaments connecting the sacrum to the rest of the pelvis, requiring aggressive intervention.
Treatment Options for Healing the Sacrum
Treatment for a sacral fracture depends entirely on its stability and whether there is associated nerve damage or significant displacement. For stable, non-displaced fractures, conservative management is the standard approach. This treatment centers on pain control and activity modification to allow the bone to heal naturally. While rest is necessary, prolonged bed rest is discouraged to prevent complications like deep vein thrombosis, pneumonia, and muscle atrophy.
Patients are encouraged to begin early, progressive mobilization, such as walking with assistive devices like a walker or crutches, as tolerated by their pain level. Pain management may involve non-opioid and sometimes short-term opioid medications. In some cases, a supportive brace or orthosis may be used for comfort. This non-surgical pathway aims for a controlled return to weight-bearing activities over several weeks.
Surgical intervention becomes necessary for unstable fractures, those with significant displacement, or any fracture causing neurological compromise. The primary goal of surgery is to restore the alignment of the sacrum and the pelvic ring, providing a stable environment for healing. Common surgical techniques include:
- Percutaneous iliosacral screws, placed through small incisions to stabilize the fracture by connecting the sacrum to the ilium.
- Triangular osteosynthesis, used for highly unstable patterns (such as U-shaped or bilateral vertical fractures), which connects the sacrum to the lower lumbar spine using screws and rods.
- Sacroplasty, a minimally invasive procedure for insufficiency fractures in osteoporotic patients, involving the injection of bone cement to stabilize the fractured area.
Prognosis and Rehabilitation
The recovery timeline for a sacral fracture varies widely, depending on the severity and whether surgical stabilization was required. For stable, non-displaced fractures treated non-surgically, healing often takes between eight to twelve weeks before a patient can resume most normal daily activities. For severe, unstable fractures, especially those involving surgery, recovery may be protracted, potentially lasting four to six months before significant strength and mobility return.
Physical therapy (PT) is an indispensable component of the rehabilitation process once the acute pain subsides and the fracture has achieved initial stability. A structured PT program focuses on restoring range of motion and building strength in the core, hip, and pelvic muscles, which are essential for supporting the stabilized sacrum. Early therapeutic exercises involve gentle movements and progressive weight-bearing to encourage bone healing and prevent stiffness.
Most patients achieve a good functional outcome, but the potential for long-term complications is greatest in fractures with initial neurological involvement. Even after the bone heals, some individuals experience persistent low back or buttock pain, particularly if the fracture was vertically unstable. Residual neurological symptoms, such as chronic pain, weakness, or permanent dysfunction of the bladder or bowel, can occur following severe nerve damage. Full return to high-impact physical activity is not advised until at least three to four months post-injury, and only with clearance from the treating physician.