Sacral Fractures

Plain radiographs. They miss 30-50% of sacral fractures, so a normal film does not exclude one. Each view has a limited job:

• AP pelvis: often inadequate; look for asymmetry, cortical disruption and disrupted foraminal lines
• Lateral sacrum: better visualisation and an assessment of kyphosis, but still often inadequate
• Ferguson view (AP sacrum): a 30-degree cephalad tilt that shows the foramina better; rarely used in acute trauma

CT is mandatory. It defines the fracture pattern precisely and is the basis of classification and surgical planning. Read it for the Denis zone, a transverse versus longitudinal line, displacement and comminution, foraminal compromise, sacral canal involvement and associated pelvic injuries. 3D reconstruction is excellent for surgical planning, demonstrates complex patterns and is a communication tool.

MRI. Indicated for a neurological deficit, suspected cauda equina compression, insufficiency fractures (the oedema pattern) and soft-tissue assessment. It shows nerve root compression, canal stenosis, bone marrow oedema and soft-tissue injury.

View larger

View larger

Differential diagnosis. Low back, buttock or sacral pain, especially the insidious insufficiency-fracture presentation, has several mimics. The key discriminators are mechanism, MRI signal pattern and red-flag features.

Indications. Conservative treatment suits:

• Zone I with minimal displacement (less than 5mm)
• A stable pelvic ring
• No neurological deficit
• Insufficiency fractures, as first line

Protocol. Bed rest for the first 2-4 weeks, then progressive, pain-guided mobilisation with walking aids and weight-bearing as tolerated, supported by physiotherapy. Analgesia runs from paracetamol and NSAIDs to opioids, with LMWH as DVT prophylaxis. Serial radiographs are taken at 1, 2 and 6 weeks.

Expected course. Most heal at 6-12 weeks. Return to function is gradual, and late complications are watched for.

Absolute indications.

• Neurological deficit with canal compromise
• Unstable pelvic ring
• Spinopelvic dissociation (U-type, H-type)
• Progressive neurological deterioration
• Zone III with cauda equina syndrome

Relative indications.

• Significant displacement (greater than 1cm)
• Zone III fractures even without deficit
• Associated pelvic ring injury requiring stabilisation
• Failure of conservative management
• Polytrauma requiring early mobilisation

The options are percutaneous SI screws, lumbopelvic fixation, sacral decompression and, for insufficiency fractures, sacroplasty. Each is described under Surgical Technique.

Immediate surgery is required for:

• Cauda equina syndrome with canal compromise
• Progressive neurological deterioration
• Spinopelvic dissociation with instability
• Zone III fracture with neurological deficit

The approach is posterior sacral decompression with lumbopelvic fixation, and a combined procedure is often needed.

Timing. Decompression within 24-72 hours is associated with the best results, the aim is under 72 hours if possible, and earlier decompression is associated with better neurological recovery. Hold that association loosely. Denis's own claim that decompression improved recovery was labelled preliminary and was uncontrolled, and in Lindahl's 36 H-type dissociations the timing of surgery and laminectomy were not associated with outcome, whereas accurate reduction was.

Percutaneous sacroiliac screws. Indicated for Zone I and II fractures, longitudinal sacral fractures, SI joint instability, and stable to moderately unstable patterns. The patient lies supine on a radiolucent table, with lateral decubitus as the alternative. The implants are 7.3mm or 7.0mm cannulated screws over guidewires with cannulated instruments, under fluoroscopy in inlet, outlet and lateral views.

Steps.

1. Imaging set-up. A true inlet view (beam angled caudally, roughly 40 degrees) judges anterior-posterior translation; a true outlet view (beam angled cephalad, roughly 40 degrees) shows the foramina and vertical translation. Add a lateral sacral view and mark the S1 body corridor.
2. Entry point. Posterior ilium lateral to the SI joint, approximately 1cm superior to the greater sciatic notch, avoiding the L5 nerve anteriorly.
3. Guidewire. Advance under fluoroscopy, checking all three views continuously, targeting the S1 body (the safe zone) and avoiding the sacral canal medially and a breach of the anterior cortex.
4. Screw. Measure the guidewire depth, insert the cannulated screw over the wire, ensure bicortical purchase and confirm the final position in all views.
5. S2 screw (optional). For greater stability, entered more cephalad with a similar technique.

Dangers. The L5 nerve anterior to the ala, the sacral canal medially, the anterior vascular structures, and dysmorphic sacral variants.

View larger

View larger

Lumbopelvic fixation (triangular osteosynthesis). The construct bypasses the unstable sacrum entirely, joining the spine to the pelvis in a triangular pattern. It is indicated for spinopelvic dissociation, bilateral sacral fractures, Zone III fractures, U-shaped or H-shaped patterns, and failed SI screw fixation.

Steps.

1. Position prone on a radiolucent frame, arms tucked or out on boards.
2. Expose through a posterior midline incision from L3/L4 to the sacrum, with bilateral paraspinal dissection to the L4/L5 pedicles and both posterior ilia.
3. Lumbar pedicle screws at L4 and/or L5, freehand or navigated, usually 6.5mm or 7.0mm polyaxial screws.
4. Iliac screws enter the posterior ilium directed toward the ASIS between the inner and outer tables. They are long (70-90mm), and bicortical fixation is ideal.
5. Rods are measured, contoured and connected from the lumbar to the iliac screws on both sides, applying compression or distraction as needed.
6. Final construct. Tighten all set screws, confirm a stable construct and check it on fluoroscopy.

Trade-offs. The construct is very stable, bypasses the fracture, allows early mobilisation and gives good results in dissociation injuries. The price is a large exposure, a longer operation, possible implant prominence and a risk of adjacent segment degeneration.

View larger

View larger

Sacral decompression. Indicated for Zone III with a neurological deficit, canal compromise on CT or MRI, cauda equina syndrome and progressive neurological deterioration.

Steps.

1. Imaging. A preoperative MRI is essential to identify the level of compression and plan the extent of decompression.
2. Exposure. A posterior midline approach to the affected sacral levels, extended to L5 if needed.
3. Decompression. Sacral laminectomy, removal of bone fragments and decompression of the neural elements, avoiding excessive retraction.
4. Stabilisation. Usually combined with fixation, commonly lumbopelvic, to prevent further instability.

Sacroplasty. Indicated for insufficiency fractures in elderly patients with osteoporotic bone and pain that persists despite 6 weeks of conservative treatment. Through a CT-guided percutaneous approach, similar to vertebroplasty, PMMA cement is injected, usually bilaterally, with pain relief as the primary goal.

What it achieves. Reported outcomes are significant pain reduction, low complication rates and good functional improvement. Set that beside the Tjardes report: the finite-element evidence it cites suggests sacroplasty alone may not permanently restore the weight-bearing capacity of the sacrum, and it presents cement-augmented iliosacral screws as a more durable alternative.

View larger

Neurological injury. The most significant complication, at the zone-dependent rates set out under Classification. It may be permanent, especially in Zone III, so document the baseline and monitor closely.

Haemorrhage. Presacral venous plexus injury forms part of the pelvic haemorrhage of ring injuries and is usually managed with the pelvic trauma protocol. Angioembolisation is used if bleeding continues, and surgical exploration is rarely required.

Thromboembolism. Pelvic trauma carries a high DVT risk, and prolonged immobility increases it. Chemical prophylaxis with LMWH is essential, alongside mechanical compression devices and early mobilisation when possible.

Infection. Wound infection occurs in surgical cases and deep infection is rare. The risk is higher with open fractures, and prophylactic antibiotics are given per protocol.

Chronic pain. Sacroiliac dysfunction is common, in 30-40%, alongside neuropathic and mechanical pain. Management may need to be multimodal and multidisciplinary, with SI joint injections and pain clinic referral; SI joint fusion is rarely needed. Post-traumatic SI joint arthritis is possible, usually develops years later and is managed conservatively at first.

Malunion. In transverse fractures malunion takes the form of kyphotic deformity. A leg length discrepancy is possible, with gait abnormality and SI joint dysfunction, and corrective surgery may be needed.

Nonunion. Rare with adequate fixation (less than 5%) and more common with conservative treatment. It may need revision surgery with bone grafting and rigid fixation.

Sexual, bowel and bladder dysfunction. All three follow S2-S4 root injury. Sexual dysfunction, erectile dysfunction in men and loss of vaginal sensation in women, may be permanent and impacts quality of life significantly, so counselling is important. Bowel and bladder dysfunction may require long-term management, multidisciplinary with urology and colorectal consultation, intermittent catheterisation and a bowel regimen.

Neurological sequelae. Permanent deficits persist in 20-30% of Zone III injuries, and chronic neuropathic pain may follow.

Implant problems. Screw malposition, nerve injury from a screw, implant prominence after lumbopelvic fixation and, rarely with modern techniques, implant failure. Implants may require removal (10-15%), usually after union at more than 12 months.

View larger

View larger

Monitoring. Neurological observations, especially if decompression was performed, with motor and sensory function checked four-hourly initially, bowel and bladder function, wound checks and DVT prophylaxis.

Analgesia. Multimodal, with intravenous opioids initially and transition to oral medication, adding neuropathic agents (gabapentin, pregabalin) if needed. Early pain control is essential for neurological recovery and patient comfort.

After SI screw fixation. Touch weight-bearing for 6 weeks, progressive weight-bearing from 6 to 12 weeks, and full weight-bearing at 12 weeks if the radiographs show healing.

After lumbopelvic fixation. The construct is more stable than SI screws alone and usually allows earlier mobilisation: touch to partial weight-bearing immediately, then progressive weight-bearing as tolerated.

Conservative management follows the protocol under Management Algorithm. Every protocol must be individualised to the fracture pattern and the fixation method.

Serial examination. Examine repeatedly over the first 48-72 hours and document any deterioration immediately. The critical checks are L5 motor (great toe extension, ankle dorsiflexion), S1 motor (ankle plantarflexion, ankle jerk) and S2-S4 bowel and bladder function.

Bladder. Intermittent catheterisation if there is retention, avoiding a prolonged indwelling catheter, and urology consultation if dysfunction persists.

Bowel. A bowel regimen of stool softeners and fibre, monitoring for constipation, and colorectal consultation if dysfunction is severe.

Phases. Rehabilitation runs in three stages:

• Early (0-6 weeks): bed mobility, transfer training, gait training with assistive devices and gentle core strengthening
• Intermediate (6-12 weeks): progressive weight-bearing, strengthening, proprioception training and return to activities of daily living
• Late (greater than 12 weeks): advanced strengthening, functional training and return to sport or work

Follow-up. Radiographs at 2 weeks (first postoperative check), 6 weeks (healing, adjusting weight-bearing), 12 weeks (union) and 6 months (final assessment), with further imaging if symptoms persist. Each clinical review covers the neurological examination, pain, function and any implant-related concern.

Union. SI screw fixation achieves union in greater than 90% and lumbopelvic fixation in greater than 85%, with higher rates the more stable the fixation. Union typically occurs within 12-16 weeks with appropriate management.

Without surgery. Most fractures heal with conservative treatment, and insufficiency fractures have good healing rates, but residual pain may persist even with union.

By zone. Zone I carries a better prognosis than the central zones, and Zone III the poorest:

• Zone I (L5): 50-70% recover if the deficit is incomplete, but a foot drop may be permanent and may need a long-term AFO
• Zone II (S1-S2 roots): recovery is variable; plantarflexion weakness often persists and sensory deficits are common, though functional outcomes are usually acceptable
• Zone III (cauda equina): complete injuries rarely recover fully, bowel and bladder dysfunction is often permanent and sexual dysfunction may persist; incomplete injuries have a better prognosis

What predicts recovery. The severity of the initial deficit and whether it is complete or incomplete, the zone of injury, the timing of decompression if performed, and age, with younger patients doing better. Recovery is highly variable.

Return to work. Sedentary work at 3-6 months and physical labour at 6-12 months. Job modification may be required, and neurological deficits affect the timeline.

Return to sport. Low-impact activities at 4-6 months, high-impact sports at 6-12 months and contact sports at a minimum of 12 months, depending on fracture healing and stability.

Quality of life. Most patients have a good functional recovery, but chronic pain is common, neuropathic pain can be challenging and sexual dysfunction impacts quality of life. Psychological support is important, and multidisciplinary support optimises functional outcomes and quality of life.