Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P18. Four-rod construct is needed to maximally decrease rod strain across lumbosacral junction with TLIF but not ALIF in long segment fixation

Abstract

BACKGROUND CONTEXT Pseudoarthrosis and rod fracture at the lumbosacral junction remain common complications in long segment fusion constructs, and may stem from increased rod and screw strain across this level. Clinical and biomechanical studies have demonstrated the benefit of using multiple rods as a strategy to reduce strain and limit rod fracture rates in constructs involving 3-column osteotomies. Studies have also suggested the benefit of using anterior lumbar interbody fusion (ALIF) at the L5/S1 disc space to provide a greater base of support compared to transforaminal lumbar interbody fusion (TLIF). However, use of multiple rods across the lumbosacral junction to reduce strain across the lumbosacral junction in long segment fusion has not been previously investigated in either the setting of ALIF or TLIF at L5/S1. PURPOSE The objective of the study was to investigate the impact of four-rod fixation on lumbosacral stability and strain in long segment constructs with either ALIF or TLIF interbodies at L5/S1. STUDY DESIGN/SETTING In vitro biomechanical study using human cadaveric specimens. PATIENT SAMPLE A total of 14 (L1-pelvis) cadaveric spines (5F/9M, 51.6±7.4 years, DEXA 0.837 g/cm 2 ). OUTCOME MEASURES Range of motion stability, L5–S1 rod strain, and sacral screw bending loads. METHODS Standard nondestructive flexibility (7.5 Nm) and compression (400 N) were performed on 14 cadaveric specimens (L1-ilium) to assess range of motion stability (ROM), rod strain (RS), and sacral screw strain (SS) of four-rod condition (+4R) versus two-rod condition (+2R); specimens were equally divided into either ALIF or TLIF at L5–S1. 5 conditions were tested: (1) noLIF+2R, (2) ALIF+2R and (3) ALIF+4R, or (4) TLIF+2R and (5) TLIF+4R. Strain gauges were used to measure rod strains (RS) at L5–S1 and net sacral screw (SS) bendng moments. Data were analyzed using RM-ANOVA or ANOVA followed by Holms-Sidak paired analysis (p RESULTS Both ALIF and TLIF provided significant decrease in ROM in C, F (p .07). TLIF+4R significantly reduced RS relative to no LIF in F (p=.004), but TLIF+2R did not (p>.07); ALIF+2R/ALIF+4R both significantly reduced RS in C, E, F(p .112). In contrast, ALIF+4R and ALIF+2R significantly reduced SS compared to TLIF+4R in C, E, and F(p CONCLUSIONS Although ALIF+2R provides greater RS reduction across the lumbosacral junction than TLIF+2R, use of 4R fixation with TLIF can nullify the difference in RS between LIF conditions. However, this comes at the cost of increased SS in TLIF+4R.