Posterior Pelvic Ring ORIF (Sacral and Crescent Fractures)

Indication. Open posterior pelvic ring ORIF is reserved for unstable posterior ring injuries that cannot be reduced or stabilised percutaneously — irreducible displacement, fractures that defeat safe screw corridors, and dissociation patterns that disconnect the spine from the pelvis. Absolute indications for open posterior ORIF - Irreducible posterior pelvic ring displacement greater than 1 cm after attempted closed reduction

• Comminuted sacral fractures with sacral dysmorphism that precludes safe percutaneous iliosacral screw placement
• Crescent fractures with intra-articular SI joint extension or significant displacement
• Spinopelvic dissociation (U-type, H-type, T-type sacral fractures) with or without neurologic deficit
• Open pelvic fractures with posterior ring involvement requiring debridement and stabilisation
• Associated lumbosacral plexus injury requiring direct exploration and decompression Relative indications - Failed percutaneous iliosacral screw fixation with loss of reduction
• Delayed presentation with malreduction that cannot be corrected percutaneously
• Poor bone quality requiring augmented fixation (osteoporosis, metabolic bone disease)
• Concomitant acetabular fracture requiring extensile exposure Contraindications Absolute: - Haemodynamic instability precluding prolonged surgery (damage-control orthopaedics first)
• Active infection at the surgical site
• Severe soft-tissue degloving (Morel-Lavallée) not yet debrided and stable Relative: - Patient factors precluding prone positioning (severe pulmonary injury, spinal instability)
• Anticipated poor wound healing (steroids, smoking, diabetes) — consider staged or percutaneous alternatives Timing and damage-control. Early stabilisation within 72 hours reduces mortality and pulmonary complications in polytrauma patients, but posterior pelvic approaches in the presence of degloving injuries carry high wound complication rates. Many centres therefore favour a staged approach: anterior external fixation or percutaneous anterior ring fixation for resuscitation, serial debridement of Morel-Lavallée lesions, and definitive posterior ORIF once the soft tissues permit — typically 5 to 14 days after injury. Consent. Counsel specifically for neurologic injury (L5 or sacral root, 3 to 8 percent), wound breakdown and infection (10 to 20 percent), hardware prominence requiring later removal (15 to 25 percent), nonunion or malunion (5 to 10 percent), and the likelihood of staged procedures if the soft tissues are compromised.

The goal is to reduce the posterior ring under direct vision and fluoroscopy and to stabilise it with a construct matched to the injury pattern — tension-band plating for crescent and rotationally unstable injuries, a transiliac internal fixator when the soft-tissue envelope is poor, and lumbopelvic fixation for spinopelvic dissociation. The exposure below is the heart of the operation: a posterior approach that elevates the gluteus maximus as a flap, protects the sciatic notch contents, and brings the sacral ala and SI joint into view.

View larger

Immediate post-operative (day 0 to 7) - Mobilisation: log-roll only for the first 48 to 72 hours with no direct pressure on the posterior wound; begin bed-to-chair transfers with assistance once drains are removed.

• DVT prophylaxis: low-molecular-weight heparin from 12 hours post-operatively, continued for 4 to 6 weeks or until fully mobile.
• Drains: remove when output is less than 30 mL per 24 hours (typically day 2 to 4).
• Wound care: daily inspection; a negative-pressure dressing, if used, stays for 5 to 7 days.
• Neurologic monitoring: serial examination of L5 and S1 root function; any deterioration prompts urgent CT. Weight-bearing and rehabilitation - Non-weight-bearing or toe-touch weight-bearing on the affected side for 6 to 12 weeks depending on fracture pattern and construct rigidity.
• Lumbopelvic constructs allow earlier mobilisation (within 1 to 2 weeks) because of superior stability.
• Physical therapy begins with gentle hip and knee range-of-motion once the wound is stable; progressive strengthening from 6 weeks; core stabilisation and gait training from 8 to 12 weeks.
• Return to work: sedentary duties at 3 to 4 months, manual labour at 6 to 9 months. Follow-up schedule - 2 weeks: wound check, radiographs (AP, inlet, outlet).
• 6 weeks: radiographs, assess for loss of reduction.
• 3 months: CT to confirm union if radiographs are equivocal.
• 6 to 9 months: consider hardware removal if prominence is symptomatic. Complications

Critical danger structures and exam traps

Osseous anatomy. The posterior pelvic ring comprises the sacrum (five fused vertebrae) and the posterior ilium. The SI joint is a true synovial joint anteriorly with a fibrous posterior component. Key landmarks: the posterior superior iliac spine (PSIS, palpable and the starting point for many posterior approaches), the posterior inferior iliac spine (PIIS, marks the superior border of the greater sciatic notch), the sacral foramina (S1 and S2 most relevant, lying 2 to 3 cm medial to the SI joint), and the sacral ala (the lateral mass whose anterior surface is crossed by the L5 nerve root). Ligamentous restraints. The posterior SI ligaments (interosseous, short posterior, long posterior) are the strongest stabilisers of the SI joint. In crescent fractures the posterior fragment remains attached to the sacrum via these ligaments, allowing indirect reduction through manipulation of the ilium. Neurovascular structures at risk. The L5 nerve root exits the L5-S1 foramen and courses laterally across the sacral ala about 2 cm medial to the SI joint before entering the greater sciatic notch — vulnerable during anterior retraction of the iliacus or screw placement across the ala. The sacral roots (S1 to S4) exit through the anterior and posterior foramina; the S1 root carries most of the sciatic nerve contribution, so its injury causes weak foot plantarflexion and perineal sensory loss. The superior gluteal neurovascular bundle exits the greater sciatic notch superior to the piriformis, 2 to 3 cm inferior to the PSIS, supplying gluteus medius and minimus — laceration causes abductor weakness and can produce a gluteal compartment syndrome. The sciatic nerve lies anterior to the piriformis in the notch; excessive medial retraction or posterior displacement of fragments can stretch or compress it. Soft-tissue envelope. The posterior sacral skin is thin (less than 1 cm in many patients) and lies directly on bone. The gluteus maximus originates from the posterior ilium and sacrum and is elevated as a flap during the approach. Morel-Lavallée lesions (closed degloving) are common in high-energy pelvic trauma and create large dead spaces prone to infection. Comparative outcomes of fixation constructs.

Special case: spinopelvic dissociation. U-type, H-type and T-type sacral fractures disconnect the lumbar spine from the pelvis; sagittal CT reformats show L5-S1 kyphosis and anterior sacral displacement, and a neurologic deficit (bowel, bladder, sexual dysfunction, lower-limb weakness) is present in 60 to 80 percent of cases. Fixation is lumbopelvic — pedicle screws in L5 (and L4 if more points are needed) connected to iliac or S2AI screws, with at least four points of fixation (two lumbar, two iliac), supplemented by iliosacral screws where corridors are safe. Sacral decompression (laminectomy) is performed when a deficit is present and imaging shows root compression. Union rates exceed 90 percent with modern constructs, neurologic recovery occurs in about 60 percent of patients with preoperative deficits, and hardware prominence requiring removal occurs in 15 to 25 percent.