James S. Harrop, Shiveindra Jeyamohan, and Alexander R. Vaccaro

Description

Intra-iliac screw placement entails a pelvic screw anchor used to fixate the lumbosacral spine to the pelvis for stability and deformity correction in long or multisegmental fusions, high-grade spondylolisthesis, of pelvic obliquity deformity correction.

Key Principles

Posterior intra-iliac fixation provides a biomechanical advantage over sacral instrumentation through secure anchors in the pelvis. The screws cross anterior to the sagittal vertical axis or sagittal plumb line without violating the sacroiliac joints.

Expectations

Intra-iliac fixation provides a solid distal foundation (pelvis) for the correction of spinal deformities, long spinal constructs, or high-grade spondylolisthesis.

Indications

• Long thoracic and lumbar fusions extending to the pelvis (e.g., scoliosis, trauma, low lumbar osteotomy)
  
• Neuromuscular scoliosis correction with pelvic obliquity
  
• Reconstruction procedures after sacrectomies
  
• Fixation for unstable sacral fractures
  
• Adjunct posterior stabilization method for high-grade lumbar spondylolisthesis
  
• Salvage procedures for revision lumbosacral operations

Contraindications

• Active spinal infection
  
• Pelvis insufficiency (i.e., extensive previous iliac crest bone graft harvesting)

Special Considerations

Need for plain radiographs of the thoracolumbar spine including standing long cassette views (36-inch) to evaluate coronal and sagittal balance. Plain radiographs of the pelvis as well as dynamic lateral flexion and extension images of the lumbar spine. In revision cases, particularly ones where there was prior posterior iliac crest bone graft harvest, a computed tomography (CT) scan of the pelvis provides further information.

Special Instructions, Position, and Anesthesia

• Patients are placed in the prone position on a Jackson-type frame, taking care to prevent excessive pressure on bony protuberances and the orbits.
  
• Operating table should maintain desired sagittal alignment with physiologic lumbar lordosis (e.g., four-post bed, Jackson table).
  
• A radiolucent operating table provides for the use of intraoperative fluoroscopy.

Tips, Pearls, and Lessons Learned

Placement of the iliac screw from the contralateral side of the table provides for a more optimal sense of screw trajectory. An osteotomy or harvesting bone from the posterior iliac crest can result in weakening of the insertion site. Therefore, bone graft harvesting should be planned after iliac screw placement.

Intraoperative fluoroscopy or plain radiographs can evaluate the final position of screw placement:

Placement of S1 screws should be done prior to iliac screws placement. This provides for an accurate assessment of screw-to-screw distance and optimal iliac screw to facilitate construct assembly.

Difficulties Encountered

• Breach of the cortical surfaces with the screw placement.
  
• Medial cortical wall penetration may result in injury to intrapelvis neurovascular structures, specifically the lumbosacral plexus.
  
• Violation of the sacral notch
  
  
  
  • May result in injury to the sciatic nerve
    
  • Injury to superior gluteal artery with subsequent retroperitoneal hematoma formation and blood loss
  
  
• Prominence of hardware with pressure ulceration formation and subsequent infection.

Key Procedural Steps