Lumbosacral and Pelvic Fixation Techniques

Abstract

Due to the considerable amount of motion at the L5–S1 segment, achieving bony fusion at that junction remains a challenge to spine surgeons. As such, pelvic fixation was developed and is used to help solve this problem. Prior to instrumentation, knowledge of the region’s anatomy, including the ligaments, is paramount. There are no absolute indications for when to instrument the pelvis or whether to stop at the sacrum when performing a long-segment construct, but relative indications do exist. The most widely used sacral instrumentation is the S1 pedicle screw. Because the S1 pedicles are wide with less cortical bone to allow for screw purchase, S1 screws at the end of long constructs can be prone to failure. Pelvic fixation helps protect S1 pedicle screws and, when coupled with S1 iliac screws, has been shown to enhance fusion rates at L5–S1. The two most common instrumentation methods for pelvic fixation use iliac screws and S2 alar-iliac (S2AI) screws. S2AI screws have the benefit over traditional iliac screws in that they minimize screw prominence, making it easier to attach these screws to the rest of the construct. The effect of S2AI screw trajectory on sacroiliac joint arthritis and sacroiliac pain continues to be debated.