Posterior Approach to Sacroiliac Joint

Primary Indications

Acute Sacroiliac Joint Disruption

• Vertical shear pelvic injuries (APC-III, LC-III, VS patterns)
• Combined mechanism injuries with posterior instability
• Denis Zone I and II sacral fractures with SI joint involvement
• Failed closed reduction requiring direct visualization

Complex Posterior Pelvic Ring Injuries

• Crescent fractures of the ilium with SI joint extension
• Comminuted sacral fractures requiring buttress plating
• Dysmorphic sacral anatomy precluding percutaneous fixation
• Transiliac-transsacral injuries requiring plate stabilization

Relative Indications

Percutaneous Screw Fixation Failures

• Malpositioned screws requiring revision
• Loss of fixation in osteoporotic bone
• Inadequate reduction after percutaneous technique

Chronic SI Joint Instability

• Symptomatic malunion after nonoperative management
• Progressive deformity with neurologic symptoms
• Failed conservative management (greater than 6 months)

Contraindications

Absolute

• Active infection overlying proposed incision
• Severe soft tissue injury precluding safe closure
• Medical comorbidities prohibiting surgery

Relative

• Obesity (BMI greater than 40) - consider staged fixation
• Prior posterior pelvic surgery with scarring
• Neurogenic bowel requiring prone positioning caution
• Osteoporosis requiring augmentation planning

Clinical Assessment

History and Mechanism

• High-energy trauma pattern (MVA, fall from height, crush)
• Associated injuries (hemodynamic status, visceral trauma)
• Neurologic examination (L5, S1-4 nerve roots)
• Bowel and bladder function documentation

Physical Examination

• Pelvic stability testing (carefully if unstable)
• Lower extremity alignment and leg length discrepancy
• Soft tissue envelope assessment
• Neurologic examination including perianal sensation

Imaging Protocol

Standard Radiographs

• AP pelvis with inlet and outlet views
• Full-length AP pelvis for vertical displacement
• Flamingo views (chronic instability evaluation)

CT Imaging - ESSENTIAL

• Fine-cut (1mm) axial images through sacrum
• 3D reconstructions for spatial understanding
• Identify dysmorphic anatomy (high-riding S1, transitional anatomy)
• Assess sacral ala corridors for percutaneous screw planning
• Identify sacral fracture patterns (Denis zones)

Advanced Imaging

• MRI for ligamentous injury assessment (chronic cases)
• CT angiography if vascular injury suspected
• Dynamic fluoroscopy for instability assessment

Surgical Planning

Fixation Strategy Selection

• Percutaneous iliosacral screws (simple disruption, good anatomy)
• Open posterior plating (comminution, dysmorphic anatomy, reduction needs)
• Combined anterior-posterior fixation (complete ring disruption)

Implant Selection

• SI joint-specific plates vs reconstruction plates
• Screw length and diameter planning from CT
• Augmentation planning (osteoporosis, comminution)

Team Planning

• General surgery availability (bowel injury risk)
• Vascular surgery standby (revision cases)
• Neuromonitoring consideration (sacral nerve roots)

Standard Surgical Equipment

Basic Instruments

• Pelvic reduction instruments
  • Pointed reduction forceps
  • Large ball-spike pushers
  • Schanz pins (5.0mm) for manipulation
• Standard trauma set with heavy retractors
• Cobb elevators and periosteal elevators
• Electrocautery with extended-length tip

Specialized Pelvic Instrumentation

• SI joint-specific plate systems
• Cannulated screw sets (6.5-7.3mm diameter)
• Washer options for screw purchase
• Locking vs non-locking screw options

Fluoroscopy Requirements

Imaging Equipment - CRITICAL

• Large C-arm with pelvic imaging capability
• Radiolucent table (Jackson table or standard OR table)
• Ability to obtain lateral sacral view
• Inlet and outlet fluoroscopic positioning

Fluoroscopic Views Needed

• AP pelvis
• Inlet view (caudal tilt 40 degrees)
• Outlet view (cephalad tilt 40 degrees)
• Lateral sacrum (difficult in prone position)

Patient-Specific Implants

Plate Selection Based on Injury

• Single SI joint plates (simple disruption)
• Transiliac plates (bilateral instability)
• Lumbopelvic fixation (spinopelvic dissociation)

Screw Options

• Cannulated iliosacral screws (S1, S2 corridors)
• Solid compression screws
• Augmentation screws (cement, bone graft)

Standard Prone Positioning

Positioning Technique

• General anesthesia with endotracheal intubation
• Foley catheter placement (long procedure, monitoring)
• Prone on radiolucent Jackson table or chest rolls
• Arms positioned on arm boards (less than 90 degrees abduction)

Pelvic Alignment Optimization

• Hips extended to relax gluteal muscles
• Moderate hip flexion acceptable if needed for reduction
• Pelvis tilted to correct rotational deformity if present
• Leg length equalized with bump if needed

Pressure Point Protection - CRITICAL

• Gel pads under chest (avoid brachial plexus compression)
• Forehead padding (avoid facial nerve compression)
• Knee padding (avoid peroneal nerve compression)
• Feet off end of table (avoid compartment syndrome)

Special Positioning Considerations

Obese Patients

• Extra padding required for pannus
• Consider modified lateral position if prone unsafe
• Extended positioning time increases wound complication risk

Bilateral Injuries

• Position to allow access to both sides
• May require intraoperative repositioning for optimal exposure

Associated Injuries

• Spinal cord injury patients - careful turning protocol
• Long bone fractures - appropriate splinting during positioning

Bony Landmarks

Palpable Surface Anatomy

• Posterior superior iliac spine (PSIS) - primary landmark
• Iliac crest - extends laterally from PSIS
• Sacral spinous processes - midline reference
• Ischial tuberosity - caudal landmark (rarely palpable prone)

Osseous Relationships

• SI joint lies 2-3cm medial to PSIS
• Joint orientation: 25 degrees from sagittal plane
• Sacral ala corridors: S1 (largest), S2 (variable)
• Iliac crest thickness varies (outer table vs inner table)

Neurovascular Anatomy - CRITICAL

Superior Cluneal Nerves

• Origin: Dorsal rami of L1-L3 nerves
• Course: Cross iliac crest 6-8cm lateral to PSIS
• Risk: Wound hypesthesia if transected (patient counseling needed)
• Protection: Identify and preserve if possible, or sharply divide

Deeper Neural Structures

• L5 nerve root anterior to sacral ala (1-2cm anterior to SI joint)
• S1-S4 nerve roots in sacral foramina
• Sciatic nerve exits greater sciatic notch (safe distance from approach)

Vascular Structures

• Superior gluteal artery and vein (greater sciatic notch)
• Iliolumbar vessels (superior aspect of SI joint)
• Lateral sacral vessels (anterior to sacrum - not at risk)

Ligamentous Anatomy

Posterior SI Ligaments - Strongest in Body

• Posterior SI ligament complex:
  • Short posterior SI ligament (directly over joint)
  • Long posterior SI ligament (from PSIS to S3-S4)
  • Interosseous SI ligament (deepest, strongest)
• These must be disrupted or fractured for SI joint instability

Associated Ligaments

• Sacrotuberous ligament (sacrum to ischial tuberosity)
• Sacrospinous ligament (sacrum to ischial spine)
• Iliolumbar ligaments (L5 to iliac crest)

Muscular Anatomy

Superficial Layer

• Gluteus maximus (most superficial coverage)
• Latissimus dorsi (superior lateral)
• Paraspinal muscles (medial)

Deep Layer

• Erector spinae muscles (medial to SI joint)
• Multifidus (directly over sacrum)
• Gluteus medius and minimus (lateral, not typically encountered)

Step 1: Skin Incision and Superficial Dissection

Incision Planning

• Longitudinal incision centered over PSIS
• Extends 8-10cm: 2cm superior, 6-8cm inferior to PSIS
• Positioned 2-3cm lateral to midline
• Can extend more inferiorly for transiliac plating

Skin and Subcutaneous Dissection

• Sharp incision through skin and subcutaneous tissue
• Identify and protect superior cluneal nerves (if encountered)
  • Cross iliac crest 6-8cm lateral to PSIS
  • If in field, sharply divide and cauterize (counseled preop)
• Dissect down to gluteal fascia

Fascia Incision

• Incise fascia over iliac crest in line with skin incision
• Extend fascial incision to periosteum
• Develop plane between gluteus maximus and underlying bone

Step 2: Subperiosteal Exposure of Ilium

Iliac Crest Dissection

• Subperiosteal elevation of gluteus maximus from outer table of ilium
• Cobb elevator used to sweep muscle posteriorly off bone
• Expose ilium 3-4cm posterior to PSIS
• Extend exposure inferiorly toward greater sciatic notch

Medial Dissection Toward SI Joint

• Identify PSIS as key landmark
• Subperiosteal dissection medially off posterior ilium
• Elevate paraspinal muscles from sacrum medially
• Expose posterior SI joint capsule

Exposure Limits

• Superior limit: Preserve iliolumbar ligaments if possible
• Medial limit: Posterior SI joint line (do not violate anterior SI structures)
• Inferior limit: Superior border of greater sciatic notch (gluteal vessels)
• Lateral limit: 5-6cm lateral to PSIS (adequate for plate placement)

Step 3: SI Joint Exposure and Capsulotomy

Joint Identification

• Palpate SI joint line (ridge between ilium and sacrum)
• Usually identified 2-3cm medial to PSIS
• Joint orientation runs obliquely (25 degrees from sagittal)

Capsular Incision (if needed for visualization)

• Incise posterior SI joint capsule longitudinally
• Expose joint surfaces to assess reduction
• Preserve interosseous ligaments if possible (strongest stabilizers)

Assessment of Injury Pattern

• Complete disruption vs partial tear
• Bone quality assessment
• Associated sacral fracture identification

Step 4: Reduction of SI Joint Disruption

Reduction Techniques

Option 1: Direct Manipulation

• Large pointed reduction forceps across SI joint
• One tine on ilium, one on sacrum
• Compress to reduce joint

Option 2: Schanz Pin Manipulation

• Place 5.0mm Schanz pin in iliac wing
• Use as joystick to manipulate hemipelvis
• Correct rotational and vertical displacement

Option 3: Combined Technique

• Combination of manual manipulation and instrument reduction
• May require assistant applying traction on leg

Reduction Assessment

• Fluoroscopic confirmation (AP, inlet, outlet views)
• Direct visualization of joint surfaces
• Less than 5mm displacement acceptable
• Rotational alignment critical

Temporary Fixation

• Hold reduction with pointed reduction forceps
• May use temporary K-wires (2.0mm) to hold reduction
• Maintain reduction during definitive fixation

Step 5: Definitive Fixation - Technique Options

Option A: Percutaneous Iliosacral Screw Fixation

When to Use from Posterior Approach

• Good reduction maintained
• Favorable sacral anatomy (wide S1 corridor)
• Standard injury pattern

Technique

• Stab incision lateral to main wound
• Use guidewire under fluoroscopic guidance
• Aim for S1 body (largest corridor)
• Inlet view: guidewire perpendicular to joint
• Outlet view: guidewire in S1 body (not anterior, not into canal)
• Lateral view: anterior cortex penetration confirms body placement
• Over-drill, measure, insert 6.5-7.3mm cannulated screw
• Consider washer for improved purchase

Screw Placement Principles

• S1 screw: Largest corridor, primary fixation
• S2 screw: Adds rotational stability (if corridor adequate)
• Avoid foramina (S1-S4 nerve roots)
• Bicortical purchase improves stability

Option B: Posterior SI Joint Plate Fixation

When to Use

• Dysmorphic sacral anatomy (narrow corridors)
• Need for buttress plating (comminution)
• Osteoporotic bone requiring multiple points of fixation
• Revision cases

Plate Selection

• SI joint-specific plates (pre-contoured)
• Reconstruction plates (3.5mm or 4.5mm)
• Transiliac plates (bilateral instability)

Plate Positioning

• Posterior tension band plating concept
• Plate positioned over posterior ilium and sacrum
• Spans SI joint with screws on both sides
• Contour plate to bone anatomy

Screw Insertion

• Iliac screws: Multiple cortical screws in ilium
• Sacral screws: Into S1 and S2 bodies
  • Use fluoroscopy to ensure safe trajectory
  • Avoid sacral foramina
  • Bicortical purchase if safe
• Compression across SI joint with plate screws

Biomechanical Principles

• Posterior plating resists tension forces
• May combine with anterior fixation for complete ring disruption
• Multiple points of fixation distribute load

Step 6: Fixation Verification

Fluoroscopic Assessment - MANDATORY

• AP pelvis: Screw/plate position, reduction maintained
• Inlet view: Screws not anterior to sacrum
• Outlet view: Screws not in canal or foramina
• Lateral sacrum: Screw trajectory anterior/posterior

Stability Testing

• Manual stress testing of pelvis
• Reduction maintained under stress
• No gapping at SI joint

Implant Assessment

• All screws fully seated
• Plate contoured to bone
• No prominent hardware over PSIS

Step 7: Wound Closure

Deep Layer Closure

• Re-approximate fascia over iliac crest with #1 absorbable suture
• Ensure fascia covers hardware (reduces prominence)
• Secure fascial closure (high tension area)

Subcutaneous Layer

• 2-0 absorbable suture in subcutaneous tissue
• Eliminate dead space (reduce seroma/hematoma risk)

Skin Closure

• 3-0 or 4-0 nylon interrupted vertical mattress sutures
• Ensure skin edges everted (wound over iliac crest under tension)
• May use staples (easier removal, comparable results)

Drain Placement

• Consider drain if extensive dissection
• 10Fr flat drain deep to fascia
• Remove when output less than 30mL/24hrs

Intraoperative Complications

Neurovascular Injury (Less than 2%)

• L5 nerve root injury: Rare with posterior approach (nerve is anterior)
• Sacral nerve injury: Screw malposition into foramina
  • Prevention: Fluoroscopic guidance, anatomic knowledge
  • Recognition: Intraoperative neuromonitoring changes
• Superior gluteal vessel injury: Excessive inferior dissection
  • Prevention: Limit exposure to superior border of sciatic notch

Loss of Reduction

• Inadequate temporary fixation during definitive fixation
• Poor bone quality (osteoporosis)
• Prevention: Maintain reduction forceps, consider augmentation

Hardware Malposition

• Screw into canal or foramina
• Screw anterior to sacrum (visceral risk)
• Prevention: Multiple fluoroscopic views, trajectory awareness

Early Postoperative Complications (Less than 1 month)

Wound Complications (2-5%)

• Superficial dehiscence: Most common complication
  • Risk factors: Obesity, smoking, diabetes, tension
  • Prevention: Meticulous closure, tension-free approximation
  • Management: Local wound care, may need re-closure
• Deep infection (Less than 1%):
  • Requires irrigation, debridement, hardware retention if possible
• Seroma/hematoma: Consider drain placement

Neurologic Complications

• Superior cluneal nerve numbness: Expected, counsel preop
• Transient sciatic symptoms: From positioning or retraction
• Permanent deficit: Rare (less than 1%)

Thromboembolic Events

• DVT/PE risk elevated in pelvic trauma
• Prevention: Chemical and mechanical prophylaxis
• Early mobilization when stable

Late Complications (Greater than 1 month)

Hardware-Related Issues

• Screw loosening: Osteoporosis, inadequate fixation
• Screw breakage: Excessive loading, delayed union
• Prominent hardware: Over PSIS, may require removal
• SI joint arthritis: From residual instability or malunion

Chronic Pain Syndromes

• SI joint pain from malunion or hardware
• Neuropathic pain from nerve injury
• Myofascial pain from muscle trauma

Malunion/Nonunion

• Malunion (5-10%): From inadequate reduction
  • Causes chronic pain, gait abnormality
  • May require revision surgery
• Nonunion (Less than 5%): Rare with adequate fixation

Immediate Postoperative Care (0-48 hours)

Positioning and Mobilization

• Log roll precautions for first 24 hours
• Gradual mobilization to sitting at bedside
• Early mobilization reduces DVT risk

Pain Management

• Multimodal analgesia (opioids, NSAIDs, acetaminophen)
• Consider epidural for bilateral procedures
• Local wound infiltration at closure

Wound Care

• Inspect dressing at 24-48 hours
• Watch for hematoma, dehiscence
• Drain removal when output less than 30mL/24hrs

Weight-Bearing Protocol

Isolated SI Joint Disruption with Stable Fixation

• Toe-touch weight-bearing (TTWB) for 6 weeks
• Progressive weight-bearing at 6-8 weeks
• Full weight-bearing at 8-12 weeks

Bilateral Injuries or Poor Bone Quality

• Non-weight-bearing (NWB) for 6-8 weeks
• Gradual progression based on clinical and radiographic healing

Associated Injuries

• Coordinate with other injury management
• May delay mobilization if multiple injuries

Radiographic Follow-up

2 Weeks

• AP pelvis, inlet, outlet views
• Assess reduction maintenance
• Hardware position verification

6 Weeks

• Repeat radiographs before increasing weight-bearing
• Assess early healing signs

12 Weeks

• Full radiographic series
• Assess union, no hardware loosening
• Cleared for full activities if healed

6 Months and 1 Year

• Long-term follow-up
• Assess for late complications (arthritis, hardware issues)

Physical Therapy

Phase 1 (0-6 weeks): Protection Phase

• Gentle ROM exercises (hip, knee)
• Avoid hip abduction (stresses SI joint)
• Core strengthening (isometrics only)

Phase 2 (6-12 weeks): Progressive Loading

• Progressive weight-bearing as tolerated
• Pelvic stability exercises
• Gait training

Phase 3 (12+ weeks): Functional Restoration

• Sport-specific training (if applicable)
• Return to work activities
• Ongoing core strengthening

Return to Activity

Sedentary Work: 8-12 weeks Light Labor: 12-16 weeks Heavy Labor: 4-6 months Contact Sports: 6-9 months Full Activities: 6-12 months (based on healing)

Posterior sacroiliac joint disruption is a significant component of high-energy pelvic trauma managed across Australian major trauma centers, particularly in states with high road traffic accident rates and mining/industrial injuries. The Australian and New Zealand Orthopaedic Trauma Society (ANZOTS) emphasizes early definitive fixation in hemodynamically stable patients, with posterior SI joint stabilization performed within 48-72 hours of injury when possible to facilitate early mobilization and reduce ICU length of stay.

Management of SI joint disruption in Australia follows international best-practice guidelines with strong emphasis on CT-based surgical planning. Most major trauma centers (Royal Adelaide Hospital, Royal Melbourne Hospital, Royal Brisbane Hospital, Westmead Hospital) have adopted percutaneous iliosacral screw fixation as first-line treatment for simple SI joint disruptions, reserving open posterior plating for complex patterns including dysmorphic sacral anatomy (more common in certain populations), severe osteoporosis, or comminuted sacral fractures. The learning curve for percutaneous technique has been addressed through structured fellowship training programs and cadaveric workshops supported by the Australian Orthopaedic Association (AOA).

Anterior approaches to the SI joint are rarely performed in Australian practice due to high L5 nerve root injury rates (5-15%) and availability of posterior fixation techniques that achieve equivalent stability with lower morbidity. When complete pelvic ring disruption requires both anterior and posterior fixation, staged procedures are common - anterior ring fixation (symphyseal plating or superior ramus screws) followed by posterior SI fixation once the patient is hemodynamically stable. Antibiotic prophylaxis follows Therapeutic Guidelines (eTG) recommendations with cefazolin 2g IV at induction, with additional intraoperative doses for procedures exceeding 4 hours. Patients are counseled regarding superior cluneal nerve numbness (occurs in most posterior approaches) and the expected 8-12 week non-weight-bearing rehabilitation period, with coordination with state-based workers' compensation schemes (WorkCover, icare) for occupational injuries common in mining and construction sectors.