Sacral Fracture
Fracture of the sacrum from trauma or insufficiency in osteoporotic bone
ICD-10: S32.10 · sacroiliac condition
Sacral fractures are breaks in the triangular bone at the base of the spine that connects the two iliac bones of the pelvis. They span a wide spectrum: high-energy traumatic sacral fractures associated with pelvic ring injuries, vertical shear, and potential neurological deficits; and low-energy sacral insufficiency fractures in elderly osteoporotic patients, sometimes occurring with minimal or no trauma. Traumatic sacral fractures are classified by the Denis zone system: Zone I (alar, lateral to sacral foramina) — lowest neurological risk; Zone II (transforaminal, through sacral foramina) — 28% neurological injury rate; Zone III (central canal) — 57% neurological injury rate including bowel and bladder dysfunction. Vertical shear (Tile C) and U-type (bilateral vertical + horizontal) fractures carry the highest neurological injury risk and require surgical stabilization. Low-energy sacral insufficiency fractures present in elderly women with osteoporosis, radiation-induced bone fragility, or corticosteroid use. They cause bilateral deep buttock and sacral pain worsened by weight-bearing, often without a clear traumatic event. The classic MRI appearance of bilateral sacral alar fractures with a horizontal fracture creating an "H-pattern" (Honda sign) on bone scan is diagnostic. Treatment ranges from protected weight-bearing to sacroplasty or surgical stabilization depending on severity.
Anatomy & Pathology
The sacrum is a triangular bone formed by five fused vertebrae (S1–S5) at the base of the spine. It articulates with the iliac bones of the pelvis at the sacroiliac joints on each side and connects to the coccyx (tailbone) below. The sacral foramina — small openings along its surface — allow the sacral nerve roots to exit, carrying signals that govern lower-limb movement and pelvic organ function. The sacrum's position makes it a load-bearing keystone transferring body weight from the spine into the pelvis and legs.
Symptoms
- Severe low back, sacral, and buttock pain after trauma or fall
- Inability to bear weight
- Leg weakness, perineal numbness, or bowel/bladder dysfunction (high-zone fractures)
- Deep bilateral sacral and buttock aching in insufficiency fractures (elderly)
- Pain worsened by sitting and standing, relieved by lying flat (insufficiency fractures)
- Bruising and swelling over the sacrum and posterior pelvis (traumatic)
- Positive FABER and FADIR tests (groin and buttock pain provocation)
Causes & Risk Factors
- High-energy trauma: motor vehicle accident, fall from height, crush injury
- Pelvic ring disruption with associated sacral fracture component
- Osteoporosis causing insufficiency fractures from minor or no trauma
- Radiation therapy to the pelvis causing radiation osteonecrosis and fragility
- Repetitive stress in endurance athletes (sacral stress fracture — rare)
Treatment Options
Conservative
- Protected weight-bearing with walker or crutches for stable Zone I fractures and insufficiency fractures
- Analgesic management including calcitonin (reduces pain in osteoporotic fractures)
- Osteoporosis treatment: bisphosphonates, denosumab, teriparatide to prevent future fractures
Surgical
- Iliosacral screw fixation for unstable Zone I–II fractures or pelvic ring injuries
- Sacroplasty (fluoroscopy-guided cement augmentation) for refractory osteoporotic insufficiency fractures
- Lumbopelvic stabilization (spinopelvic fixation) for U-type and high-grade bilateral vertical shear fractures with neurological deficit
When to see a spine specialist
Any fall or injury followed by severe pelvic, sacral, or buttock pain requires emergency evaluation to exclude a sacral fracture, pelvic ring injury, and neurological injury. Elderly patients with new bilateral deep sacral pain after minor trauma should be evaluated by MRI (more sensitive than plain radiographs) to identify insufficiency fractures often missed on X-ray.
Specialists Who Treat Sacral Fracture
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Search spine specialists →Frequently Asked Questions
Can a sacral fracture be missed on plain X-ray?
Yes, commonly. Sacral fractures — especially insufficiency fractures — are missed on plain radiographs in up to 30–50% of cases due to the overlying bowel gas, the oblique sacral anatomy, and the subtle bone changes in insufficiency-type fractures. MRI is the gold standard for detecting sacral insufficiency fractures (shows bone marrow edema). CT is better for characterizing traumatic fracture patterns. A high index of suspicion and advanced imaging is required when X-rays are negative but clinical suspicion persists.
What is the Denis zone classification for sacral fractures?
The Denis system classifies sacral fractures by relationship to the sacral foramina: Zone I fractures are in the alar (lateral wing) and carry low neurological risk (~6%); Zone II fractures run through the sacral foramina and have 28% neurological injury risk affecting the L5, S1 nerve roots; Zone III fractures involve the central sacral canal and have the highest neurological risk (~57%), potentially causing cauda equina injury with bowel, bladder, and sexual dysfunction.
What is sacroplasty and who is a candidate?
Sacroplasty is a minimally invasive procedure in which polymethylmethacrylate (PMMA) bone cement is injected into the fractured sacrum under fluoroscopic or CT guidance to stabilize the fracture and reduce pain. It is analogous to vertebroplasty for vertebral compression fractures. Candidates are patients with osteoporotic sacral insufficiency fractures who have not responded to 4–6 weeks of conservative management. Pain relief is typically immediate and dramatic in well-selected patients.