5. A biomechanical investigation of the sacroiliac joint in the setting of lumbosacral fusion: the impact of pelvic fixation vs sacroiliac joint fixation

Abstract

BACKGROUND CONTEXT The sacroiliac (SI) joint is a known source of lower back pain. Randomized clinical trials support sacroiliac fusion over conservative management for sacroiliac joint dysfunction. Clinical experience suggests degeneration of the sacroiliac joint in the setting of lumbosacral fusions. However, there are limited biomechanical studies to understand the effect of lumbosacral fusion on the sacroiliac joint. This study is a biomechanical investigation to understand the effect of pelvic vs sacroiliac joint fixation on the sacroiliac joint in lumbosacral fusion. Furthermore, researchers studied the effect of lumbosacral fixation on the SI joint in the absence of pelvic and SI joint fixation. PURPOSE To determine the immediate stability of various lumbopelvic fixation constructs. STUDY DESIGN/SETTING In-vitro biomechanical range of motion testing. METHODS Seven fresh-frozen human cadaver specimens were used. There was one intact and 6 operative constructs: (1) posterior pedicle screws and rods from T10–S1 (PS); (2) PS+bilateral iliac screw fixation (BIS); (3) PS+unilateral iliac screw fixation (UIS); (4) PS+UIS+3 contralateral unilateral SIJ screws (UIS+3SIJ); (5) PS+3 unilateral SIJ screws (3SIJ); and (6) PS+6 bilateral SIJ screws (6SIJ). A custom-built 6 degrees-of-freedom (6DOF) testing apparatus was used to simulate 3 bending modes: flexion extension (FE), lateral bending (LB), axial rotation (AR). Range of motion was recorded at L5–S1 and sacroiliac joint. RESULTS All 6 operative constructs had significantly reduced ROM at L5–S1 compared to the intact specimen in all 3 bending modes (p CONCLUSIONS This biomechanical investigation demonstrated the effects of various fusion constructs using pelvic and sacroiliac fixation in lumbosacral fusion. It adds biomechanical evidence to the literature showing adjacent segment stress in the SIJ in fusion constructs to S1. Unilateral pelvic fixation or SIJ fusion led to appreciable but nonsignificant reduction to the unfused contralateral SIJ. Finally, bilateral pelvic fixation showed the greatest significant reduction of movement at L5–S1 and was equivalent to bilateral sacroiliac fusion in reducing SIJ motion. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.