Procedure notes
Fusion to the pelvis in spine surgery can be difficult because of the complex anatomy of the lumbosacral region, the decreased bone density of the sacrum, and the large biomechanical stress placed on fixation at this transitional zone between the mobile lumbar spine and the far less mobile sacrum. Nevertheless, rigid fixation to the pelvis is crucial in many situations, particularly when maintaining sagittal alignment, and minimizing the risk of pseudarthrosis and hardware failure is of utmost importance.
Pelvic fixation has evolved over the years from its beginnings in the early 20th century with spinous process and sublaminar wiring to Harrington rods and hooks via sacral bars to the more recent Galveston technique, which first used the ilium for fixation. Although sacral pedicle screws are becoming more commonplace, the workhorses of spinopelvic fixation are iliac screws and bolts, which are the focus of this chapter. These principles of fixation and fixation techniques can also be used in sacropelvic trauma.
Several biomechanical studies have shown that sacral pedicle screws alone, such as those at S1 and S2, are prone to failure under less load than when they are used in combination with additional pelvic fixation, the most effective being the iliac bolt. It has been shown that the addition of iliac screws resulted in the most significant decrease in the strain on S1 screws and significantly increased the load to failure compared with several other methods of pelvic fixation, such as any other point of additional fixation, including multiple sacral pedicle screws.
Indications
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Long segment fusions to the sacrum, particularly in patients prone to L5-S1 pseudarthrosis, such as patients with global or lumbar sagittal imbalance or bony deficiency
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Degeneration caudad to long segment fusions
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High-grade spondylolisthesis
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Correction of pelvic obliquity
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Correction of flat back syndrome requiring osteotomy
Contraindications
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There are no absolute contraindications, but there are relative contraindications such as:
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Previously harvested iliac crest bone graft, because this can make fixation more difficult
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Severe osteoporosis
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Prior nonunion or malunion of an iliac fracture, which can alter the anatomy and reduce the quality of bone for fixation
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Planning and positioning
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When the patient is positioned, adding a slight relative kyphosis in the sagittal plane allows for better access to the structures of the lower lumbar spine and pelvis.
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Two different paths can be used for the trajectory of the iliac screws. The starting point for both is the posterior superior iliac spine (PSIS). The target for path A is the superior rim of the acetabulum, which places the hip joint at risk and is less desirable. Path B aims for the anterior inferior iliac spine (AIIS) and usually accommodates a longer screw and is safer.
Figure 78-2:
Paths in the pelvis for the trajectory of iliac screws.
Figure 78-3:
Cross section of the ilium at the level of the sciatic notch with paths indicated.
