Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P16. Iliac screws may not be necessary in long segment constructs with L5-S1 ALIF: cadaveric study of instrumentation strain.

BACKGROUND CONTEXT Lumbosacral pseudoarthrosis and instrumentation failure is common with long segment constructs. Optimizing lumbosacral construct biomechanics may help to reduce failure rates. The influence of iliac screws and interbody type on lumbosacral stability and instrumentation bending strain is not well established. PURPOSE This study investigated the effects of TLIF, ALIF, and iliac screws on long segment lumbosacral construct biomechanics. STUDY DESIGN/SETTING In vitro biomechanical study using human cadaveric specimens. PATIENT SAMPLE 14 (L1-pelvis) cadaveric spines (5F/9M, 51.6±7.4years, DEXA 0.837 g/cm2) OUTCOME MEASURES Range of motion (ROM), sacral screw bending strain (SS), and L5-S1 rod strain (RS). METHODS Fourteen human cadaveric spine (L1-ilium) specimens were prepared and potted at L1 and ilium. Specimens were equally divided into either an L5-S1 ALIF or TLIF group. All specimens underwent testing in the following conditions: (1) Intact (2) L2-S1 pedicle screw fixation (PSF) (3) L2-ilium (PSF-I) (4) PSF+ALIF (ALIF-S) or TLIF (TLIF-S) (5) PSF-I + ALIF (ALIF-I) or TLIF (TLIF-I). Pure moment bending (7.5 Nm) in flexion (F), extension (E), lateral bending (LB), axial rotation (AR) and axial compressive (C) loads (400 N) were applied to all conditions and ROM, SS, and RS were measured. Statistical comparisons were performed using one-way ANOVA (p<.05). RESULTS ALIF-S and TLIF-S provided similar decreases in ROM as TLIF-I (p>.05). Compared to PSF, iliac screws significantly decreased SS during bending in all directions (p<.01) except lateral bending (p>.16) but increased RS in flexion and extension (p<.03). ALIF-S provided similar decreases in SS as TLIF-I in all directions (p>.40). TLIF-S had more SS than TLIF-I in F,E,AR (p<.02). ALIF-S had significantly less rod strain than TLIF-I in F,E,C (p<.02) while TLIF-S had less rod strain only in E (p=.04). Compared to PSF-I, ALIF-I decreased the RS (p<.03) but TLIF-I did not have a significant effect (p>.64). CONCLUSIONS Iliac screws were most protective of SS but resulted in increased RS. Constructs with ALIF and no iliac screws provide comparable decreases in SS as constructs with TLIF and iliac screws; furthermore, RS was significantly less. If iliac screws are utilized for fixation, ALIF but not TLIF reduces the RS induced by iliac screws. [ABSTRACT FROM AUTHOR]