Pelvic Ring External Fixation

Surgical Indications

Absolute Indications

• Haemodynamically unstable patient with APC II-III or vertical shear pelvic ring injury and persistent hypotension despite pelvic binder and resuscitation
• Open pelvic fracture with massive haemorrhage requiring immediate volume reduction and tamponade
• Damage-control orthopaedics in the polytrauma patient with acidosis, hypothermia, and coagulopathy (lethal triad)
• Unstable pelvic ring with associated bladder or rectal injury requiring urgent laparotomy and simultaneous pelvic stabilisation

Relative Indications

• APC II or LC III injury with borderline haemodynamics (transient responder) as a bridge to definitive fixation
• Vertically unstable pelvis requiring posterior C-clamp supplementation when sacroiliac screw placement is delayed by physiology
• Open-book pelvis with greater than 2.5 cm symphyseal diastasis and ongoing transfusion requirement despite binder
• Patient requiring prolonged transport or transfer to definitive trauma centre

Contraindications

Absolute:

• Stable pelvic ring pattern (APC I, LC I, isolated pubic ramus fractures) — external fixation adds morbidity without benefit
• Isolated acetabular fracture without pelvic ring instability
• Patient in cardiac arrest with no return of spontaneous circulation after 15 minutes of resuscitation

Relative:

• Severe osteoporosis or iliac wing fracture precluding adequate pin purchase
• Local soft-tissue contamination or Morel-Lavallée lesion at planned pin sites (consider alternative corridors)
• Anticipated definitive internal fixation within 24 hours in a stable patient (proceed directly to ORIF)

Evidence for External Fixation in Pelvic Trauma

Biomechanical Rationale

External fixation of the unstable pelvic ring reduces pelvic volume by 10-15 percent and increases stiffness by 50-70 percent, providing tamponade of low-pressure venous bleeding that accounts for 80-90 percent of pelvic haemorrhage. The anterior frame alone provides rotational stability but insufficient vertical control in type C injuries; posterior supplementation is required.

Damage-Control Timing and Mortality

Application of external fixation within 30-60 minutes of arrival in the haemodynamically unstable patient is associated with reduced transfusion requirements and improved survival. Delay beyond 90 minutes correlates with increased mortality from exsanguination. The combination of pelvic binder, external fixation, and selective angioembolisation forms the modern resuscitation algorithm.

Supra-acetabular versus Iliac Crest Pins

Supra-acetabular pins provide superior biomechanical stability and lower rates of loosening compared with iliac crest pins. The supra-acetabular corridor allows connection to a posterior C-clamp for vertical shear injuries. Iliac crest pins are faster to insert but have higher infection and loosening rates (greater than 30 percent by 3 weeks) and are reserved for rapid damage-control situations.

Transition to Definitive Fixation

External fixation is a temporary measure. Conversion to internal fixation within 5-7 days minimises pin-site infection and allows definitive reduction and stabilisation. Prolonged external fixation (greater than 3 weeks) is associated with pin-site infection rates exceeding 25 percent and loss of reduction in vertically unstable patterns.

Relevant Pelvic Ring Anatomy for External Fixation

Osseous Corridors for Pin Placement

Supra-acetabular Corridor (Preferred)

• Origin: anterior inferior iliac spine (AIIS) region
• Trajectory: directed posteriorly and slightly medially toward the posterior superior iliac spine (PSIS)
• Safe zone dimensions: approximately 2-3 cm wide on fluoroscopic views
• Boundaries:
  • Superior: inner table of ilium
  • Inferior: acetabular roof (must remain greater than 15 mm superior)
  • Posterior: greater sciatic notch (must remain 2 cm anterior)
  • Medial: quadrilateral surface
• Length of purchase: 80-120 mm in adult pelvis
• Biomechanical advantage: longer lever arm, better purchase in dense bone, allows C-clamp connection

Iliac Crest Corridor (Damage-Control Alternative)

• Origin: iliac crest 2-3 cm posterior to ASIS
• Trajectory: directed inferiorly and medially into the iliac wing
• Safe zone: between inner and outer tables, avoiding the sciatic notch inferiorly
• Length of purchase: 40-60 mm (shorter, less stable)
• Limitations: thin cortical bone, high cantilever forces, rapid loosening

Neurovascular Structures at Risk

Lateral Femoral Cutaneous Nerve

• Crosses the ilium 1-3 cm medial to the ASIS
• Lies in a variable fascial plane 2-5 mm deep to the outer table
• Injury incidence: up to 30 percent with supra-acetabular pins when unprotected
• Prevention: 3-4 cm incision 2 cm medial to ASIS, direct visualisation, soft-tissue sleeve with medial retraction

Superior Gluteal Neurovascular Bundle and Sciatic Nerve

• Exit the greater sciatic notch
• At risk with posterior or caudal pin placement
• Prevention: confirm pin trajectory on iliac oblique view remains 2 cm anterior to the notch

Internal Iliac Vessels and Lumbosacral Trunk

• Lie medial to the quadrilateral surface
• At risk with excessively medial or long pin penetration
• Prevention: confirm pin does not breach the inner table on pelvic inlet view

Ligamentous and Soft-Tissue Considerations

• Pelvic binder application at the greater trochanter level reduces volume by 10-15 percent
• Morel-Lavallée lesion (closed degloving) over the iliac crest increases infection risk; avoid pin placement through the lesion
• The anterior pelvic ring (symphysis and rami) provides rotational stability; the posterior ring (sacroiliac ligaments, sacrum) provides vertical stability

Positioning and Preparation

Patient position: Supine on a radiolucent fracture table or flat-top table. Both lower extremities are prepped and draped free if traction or reduction manoeuvres are anticipated. The abdomen and pelvis are widely prepped to allow laparotomy access if required. A pelvic binder remains in place until the frame is applied.

Fluoroscopy setup: C-arm positioned for rapid AP, inlet, outlet, obturator oblique, and iliac oblique views. The surgeon must be able to obtain all five views without repositioning the patient. Radiation protection for the surgical team is mandatory.

Anaesthesia: General anaesthesia with invasive arterial monitoring in the haemodynamically unstable patient. Avoid hypotension during induction. Have blood products and a massive transfusion protocol immediately available.

Consent and planning: Discuss risks including LFCN injury (up to 30 percent), pin-site infection (10-25 percent), malreduction, loss of reduction, and the need for later definitive fixation. Review pre-operative radiographs and CT to plan pin corridors and anticipate reduction manoeuvres.

Supra-acetabular External Fixation — Step-by-Step

Step 1: Pre-Insertion Reduction and Binder Management

With the patient supine, confirm the pelvic binder is correctly positioned at the level of the greater trochanters. In an open-book (APC) injury, apply manual compression through the greater trochanters or use a sheet to close the pelvis before pin insertion. In vertical shear, apply longitudinal traction to the affected limb to reduce cephalad displacement.

Step 2: Supra-acetabular Pin Site Incision and LFCN Protection

Make a 3-4 cm longitudinal incision centred 2 cm medial to the ASIS on each side. Deepen through subcutaneous fat to the fascia. Identify the LFCN as it crosses the ilium medial to the ASIS and protect it with a vessel loop or gentle medial retraction. The nerve is most vulnerable during blunt dissection and sleeve placement.

Step 3: Soft-Tissue Sleeve Placement and Pin Trajectory Planning

Insert a soft-tissue sleeve through the incision onto the outer table of the ilium at the AIIS region. Plan the trajectory from the AIIS toward the PSIS on the inner table. The corridor is visualised on the obturator oblique view as a 2-3 cm radiolucent window between the acetabular roof and the sciatic notch.

Step 4: Pin Insertion under Fluoroscopic Guidance

Advance a 5 mm or 6 mm Schanz pin through the sleeve into the outer table. Confirm the starting point on the obturator oblique view. Advance the pin under power while monitoring the iliac oblique view to ensure the trajectory remains 2 cm anterior to the sciatic notch and 15 mm superior to the acetabular roof. Stop advancement when the pin engages the inner table (confirmed on pelvic inlet view). Repeat on the contralateral side.

Step 5: Frame Assembly and Reduction Manoeuvres

Connect the two supra-acetabular pins with two transverse carbon-fibre or stainless-steel bars and one diagonal bar to form a stable anterior frame. Before final tightening, perform reduction manoeuvres: external rotation of the hemipelvis for open-book injuries, longitudinal traction for vertical shear. Tighten the frame while maintaining reduction. Confirm reduction on AP, inlet, and outlet views.

Step 6: Posterior Supplementation (Vertical Shear Injuries)

In vertically unstable injuries, apply a posterior C-clamp to the posterior superior iliac spines under fluoroscopic guidance. The C-clamp provides posterior compression and vertical stability that the anterior frame alone cannot achieve. Alternatively, plan percutaneous sacroiliac screw placement once the patient is physiologically stable.

Step 7: Final Imaging and Documentation

Obtain final AP, inlet, outlet, and Judet views to confirm reduction and pin position. Document pin depths, frame construct, and reduction achieved. Plan the timing of transition to definitive internal fixation (ideally within 5-7 days).

Post-operative Protocol

Immediate Post-operative Care (Day 0-3)

• Continue resuscitation and monitoring in ICU or high-dependency unit
• Serial haemoglobin, lactate, base deficit, and coagulation studies every 6 hours until stable
• Pin-site care: daily chlorhexidine cleaning, sterile dressings
• DVT prophylaxis: mechanical (sequential compression devices) and pharmacological (LMWH) once bleeding risk permits
• Maintain frame stability; do not allow early mobilisation or weight-bearing

Transition to Definitive Internal Fixation

External fixation is a bridge, not definitive treatment. Plan conversion within 5-7 days once the patient is physiologically stable (normalised lactate, resolved acidosis, stable haemoglobin, no ongoing transfusion requirement).

Prerequisites for conversion:

• Lactate less than 2 mmol/L, base deficit less than 4 mEq/L
• Haemoglobin stable without transfusion for 24 hours
• Coagulation normalised
• No active infection or pin-site sepsis
• CT imaging confirming pin position and residual displacement

Definitive fixation options:

• Symphyseal plating for residual symphyseal diastasis greater than 2.5 cm
• Percutaneous sacroiliac screws for posterior ring injuries (most common)
• Open reduction and internal fixation for complex sacral fractures or associated acetabular fractures
• Combined anterior and posterior constructs for vertically unstable patterns

Pin-Site Management During Transition

• Remove pins in the operating theatre at the time of definitive fixation
• Debride pin sites and send cultures if any sign of infection
• Close pin sites with absorbable sutures or allow secondary healing
• Continue antibiotics for 48 hours post-removal if pin sites were clean

Rehabilitation After Definitive Fixation

• Touch weight-bearing or partial weight-bearing (20 kg) for 6-12 weeks depending on posterior ring stability
• Progressive weight-bearing guided by radiographic healing
• Hip abductor strengthening and core stabilisation from week 6
• Return to work: 3-6 months for desk-based; 6-12 months for manual labour
• Long-term follow-up for post-traumatic arthritis, leg-length discrepancy, and chronic pain