Iliac Screws may not be Necessary in Long Segment Constructs with Lumbosacral ALIF: A Cadaveric Study of Stability and Instrumentation Strain

Presented at SMISS Annual Forum 2018
By Randall Hlubek MD
With Jakub Godzik MD, Anna Newcomb MS, Jennifer Lehrman MS, Bernardo De Andrada Pereira MD, Brian Kelly PhD, Jay Turner MD, PhD,

Disclosures: Randall Hlubek MD None Jakub Godzik MD None, Anna Newcomb MS None, Jennifer Lehrman MS None, Bernardo De Andrada Pereira MD None, Brian Kelly PhD None, Jay Turner MD, PhD A; NuVasive. B; NuVasive, SeaSpine,

Introduction:

Lumbosacral pseudoarthrosis and instrumentation failure is common with long segment constructs. Optimizing lumbosacral construct biomechanics may help to reduce failure rates. ALIF is increasingly being utilized in long segment MIS constructs, but the influence on lumbosacral biomechanics compared to TLIF is not well understood.

Aims/Objectives:

This study investigated the effects of TLIF, ALIF, and iliac screws on long segment lumbosacral construct biomechanics. We hypothesized that ALIF improves lumbosacral biomechanics compared to TLIF and obviates the need for iliac screws.

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 Rods (PSR-S) 3) L2-ilium (PSR-I) 4) PSR-S+ALIF (ALIF-S) or TLIF (TLIF-S) 5) PSR-I + ALIF (ALIF-I) or TLIF (TLIF-I). Pure moment bending (7.5Nm) in flexion (F), extension (E), lateral bending (LB), axial rotation (AR) and axial compressive (C) loads (400N) were applied to all conditions and range of motion (ROM), sacral screw strain (SS), and lumbosacral rod strain (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 PSR-S, PSR-I significantly decreased SS during bending in all directions (p<.02) but increased RS in flexion and extension (p<.02). ALIF-S provided similar decreases in SS as TLIF-I in all directions (p>.40) and had significantly less RS than TLIF-I in F, E, C (p<.01). TLIF-S had more SS than TLIF-I in F, E, AR (p<.02) while TLIF-S had less RS only in F (p=.03). Compared to PSR-I, ALIF-I decreased the RS (p<.02) but TLIF-I did not have a significant effect (p>.67).

Conclusions:

Iliac screws were protective of SS but increased RS at the lumbosacral junction. If iliac screws are utilized, ALIF but not TLIF reduces the iliac screw-induced RS. Constructs with ALIF and no iliac screws result in comparable SS as constructs with TLIF and iliac screws; furthermore, with significantly reduced RS. However, TLIF without iliac screws had significantly more SS than TLIF with iliac screws. In conclusion, iliac fixation may not be necessary in long segment constructs utilizing ALIF at L5-S1.