243. The effect of sacroiliac fusion and pelvic fixation on rod strain in thoracolumbar fusion constructs: a biomechanical investigation

Abstract

BACKGROUND CONTEXT Hardware failure is a multifactorial and challenging problem frequently encountered by spinal surgeons. A common cause of construct failure is the mechanical strain that results from excessive force placed on the spine. In implanted hardware, increased rod strain can lead to construct failure and rod fracture. Clinically significant rod fractures are associated with loss of correction as well as new onset radiculopathy, pain, radiographic signs of pseudarthrosis, and the need for surgical revision. PURPOSE To investigate the effect of sacroiliac joint (SIJ) fusion and iliac fixation on distal rod strain in thoracolumbar fusions. STUDY DESIGN/SETTING In vitro biomechanical study METHODS Seven fresh-frozen human cadaveric specimens (T9–Pelvis) were used. Six operative constructs were tested to investigate changes in rod strain at L5–S1 and S1–Ilium rods: posterior pedicle screws and rods from T10–S1 (PS); PS+bilateral iliac screw fixation; PS+unilateral iliac screw fixation; PS+UIS+3 unilateral SIJ screws; PS+3 unilateral SIJ screws; and PS+6 bilateral SIJ screws. Uniaxial strain gauges were used to measure surface strain of rods during flexion-extension motion. RESULTS In flexion-extension, bilateral iliac screws added significant strain to L5–S1 when compared to long fusion constructs that ended at S1 (PS) (p CONCLUSIONS This biomechanical study examined the effect of pelvic fixation and SIJ fusion on distal rod strain in thoracolumbar fusions. Results showed that additional fixation below S1 to the pelvis significantly increased rod strain. Unilateral pelvic screws had the highest rod strain while SIJF did not affect rod strain. The authors believe these findings can help guide surgeons when associated risk of rod failure needs to be considered. FDA DEVICE/DRUG STATUS SI-LOK Screws (Approved for this indication).