Paul T. Rubery and John T. Gorczyca

Transiliac Rod Placement

Description

A bar or rod placed transversely through the posterior iliac tubercles, posterior to the sacrum, can serve as a safe and reliable distal anchor for complex instrumentation constructs across the lumbosacral junction.

Key Principles

Force concentration at the junction of the relatively mobile lumbar spine with the relatively immobile pelvis is a significant cause of spinal instrumentation failures. The relatively poor bone stock of the sacrum compromises pedicle screw fixation. Additional anchor points enhance fixation and may decrease the incidence of instrumentation failure and pseudarthrosis.

Expectations

This technique provides additional, extraspinal fixation into relatively strong bone.

Indications

Instrumentation constructs extending proximal to L2 and crossing the lumbosacral junction. The technique can be applied in clinical situations involving particularly high-grade instability at L5-S1, as well as pseudar-throses of previous L5-S1 fusions.

Contraindications

Deficiency or absence of posterior iliac bone precludes rod placement.

Special Considerations

A preoperative computed tomography (CT) scan of the pelvis is useful to assess the adequacy of the ilium for passing the transiliac rod. Specially manufactured connectors may be required to join the transversely oriented transiliac rod to the longitudinal member of the spinal instrumentation.

Special Instructions, Position, and Anesthesia

The surgeon should carefully position the patient’s hips to preserve or reconstruct the normal sagittal contours of the spine.

Tips, Pearls, and Lessons Learned

• It is occasionally necessary to remove the medial portion of the bony posterior ridge of the sacrum to pass the transverse rod from side to side.
  
• Connection of the transverse rod to the longitudinal member of the construct is challenging, and may require specially ordered or custom-manufactured components. This is especially true in revision surgery. Furthermore, this process requires generous elevation of the gluteus maximus origin from the crista glutei to preserve its fascia for repair over the hardware.
  
• Structural interbody support placed in the L5-S1 disk will reduce strain on the posterior instrumentation.
  
• Iatrogenic sagittal plane deformity (flatback) is an inherent risk of this instrumentation technique, and surgeons must be especially cognizant of the sagittal plane.

Difficulties Encountered

• Locating the transverse bar too proximally hinders connection to the L5 and S1 screws.
  
• Inadequate bone posterior in the posterior ilium may lead to iliac channel fracture.
  
• Prominent hardware with thin overlying tissues places the patient at risk for wound problems and for symptomatic hardware.

Key Procedural Steps