A sacral fracture is a break in the sacrum, the large, triangular bone situated at the base of the spine. This injury can range from a hairline crack caused by low-energy stress to a complex fragmentation resulting from major trauma. This overview explains the nature of sacral fractures, details the different injury patterns, and describes the common methods used for diagnosis and treatment.
The Sacrum’s Structure and Role
The sacrum is a wedge-shaped bone formed by the fusion of five individual vertebrae. Located directly below the lumbar spine, it connects the spine to the pelvis through the sacroiliac joints. The sacrum acts as a central link, transmitting the upper body’s weight to the pelvic girdle and lower limbs, providing stability for activities like walking and standing. It also contains a canal that protects the lower spinal nerve roots, known as the cauda equina, which control motor and sensory function in the legs and pelvic organs.
Categorizing Sacral Fractures
Sacral fractures are categorized based on the mechanism of injury and are broadly divided into high-energy traumatic breaks and low-energy insufficiency fractures. Most sacral fractures occur in conjunction with other injuries to the pelvic ring.
High-energy fractures result from significant forces, such as motor vehicle accidents, falls from a height, or crush injuries, and are common in younger adults. These powerful impacts often cause displaced or unstable breaks associated with a higher risk of concurrent ligament damage and potential neurological injury.
Insufficiency fractures are low-energy injuries that occur when normal stresses are applied to bone weakened by conditions like osteoporosis. These fractures are frequently seen in elderly women and may result from a simple fall. Although often subtle, they cause significant pain and disability.
Physicians frequently use systems like the Denis classification to categorize the location and pattern of sacral fractures. This system divides the sacrum into three zones: Zone I (lateral wings), Zone II (nerve-containing foramina), and Zone III (central spinal canal). The risk of nerve injury increases significantly with the zone number.
Another common pattern in insufficiency fractures is the “H-type” or Honda sign, where fracture lines appear on both sides of the sacrum connected by a transverse line. This pattern often indicates spinopelvic instability, meaning the spine is no longer properly aligned with the pelvis. Classification systems help determine stability and guide treatment strategy.
Symptoms and Diagnostic Imaging
Symptoms of a sacral fracture include severe lower back, buttock, or hip pain that worsens with movement or weight-bearing activities. Patients often have difficulty standing, sitting, or walking, and the pain may radiate down the legs, mimicking sciatica. Bruising and swelling in the lower back or pelvic region may also be present following a traumatic event.
Neurological involvement is a significant concern due to the proximity of the sacral nerve roots. Signs of nerve damage include numbness, tingling, or weakness in the lower limbs. Changes in bowel or bladder control are serious symptoms suggesting injury to the cauda equina and require immediate medical evaluation.
Diagnostic Imaging
Sacral fractures are difficult to detect on standard plain X-rays because the bone’s complex shape and overlap with other pelvic structures can obscure fracture lines. Advanced imaging is required for a definitive diagnosis.
A Computed Tomography (CT) scan is commonly used to visualize the bone in detail, revealing subtle cortical disruptions or complex fracture patterns that may be missed on an X-ray. Magnetic Resonance Imaging (MRI) is highly sensitive, especially for low-energy insufficiency fractures, as it can detect bone marrow edema, which is an early sign of a stress fracture. The combination of a detailed patient history, physical examination, and appropriate advanced imaging ensures an accurate diagnosis.
Treatment and Healing Expectations
The management of a sacral fracture depends on whether the injury is stable or unstable and if there is any associated neurological deficit. Most stable, non-displaced fractures, particularly insufficiency fractures, are managed conservatively. Conservative treatment involves pain management using medication and a period of rest, followed by gradual, limited weight-bearing.
Patients undergoing conservative care are encouraged to maintain some mobility to avoid complications like blood clots and pneumonia that can result from prolonged bed rest. Surgical intervention is required for unstable or significantly displaced traumatic fractures, or those with neurological symptoms, to stabilize the pelvic ring. Surgery may involve using plates, screws, or other fixation devices to hold the fractured bone fragments in the correct position.
For stable insufficiency fractures that cause persistent pain, sacroplasty is a less invasive option. This procedure involves injecting bone cement directly into the fracture site, which stabilizes the fracture and provides rapid and long-lasting pain relief. Following the initial treatment phase, physical therapy strengthens surrounding muscles and restores mobility. The healing process can take several months, with most people seeing improvement within six to twelve weeks, though a full recovery can take up to nine months.