4. Lumbosacral TLIF but not ALIF increases proximal junction motion in long-segment constructs

BACKGROUND CONTEXT Proximal junctional kyphosis and lumbosacral (LS) pseudoarthrosis/instrumentation failure are relatively common complications following long instrumentation constructs to the sacrum. Methods to improve fusion rates and decrease instrumentation failure include LS anterior column support (ALIF or TLIF), iliac screw fixation, and accessory rods. The impact of these lumbosacral augmentation strategies on the proximal junction is not clear. PURPOSE The purpose of this study was to investigate the impact of various lumbosacral constructs on proximal junction biomechanics. STUDY DESIGN/SETTING Human biomechanical cadaveric study. PATIENT SAMPLE Twelve (L1-Pelvis) cadaveric spines were studied. OUTCOME MEASURES Proximal junction range of motion (ROM) at L1-2 was measured. 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. 4R conditions consisted of accessory rods spanning the L3-L4 and S1-Ilium levels. Compression (400 N) in combination with 7.5 Nm of flexion (FL), extension (EX), lateral bending (LB), or axial rotation (AR) was applied to all conditions. Specimens underwent testing in the following conditions: (1) intact, (2) L2-S1 pedicle screw fixation (PSR), (3) L2-ilium (PSR-I), (4) PSR+ALIF (ALIF-S) or TLIF (TLIF-S), (5) PSR-I + ALIF (ALIF-I) or TLIF (TLIF-I), and (6) ALIF-I + 4R or TLIF-I + 4R. Statistical comparisons were performed using one-way (RM) ANOVA (p RESULTS PSR-I did not significantly change proximal junction ROM in any direction compared to PSR-S (p>.069). However, TLIF-I and TLIF+4R resulted in significant increase in L1-2 ROM in FL and Right LB (p .095). ALIF-I did not significantly change ROM in any direction compared to ALIF+4R or PSR-I (p>.069). CONCLUSIONS In cadavers with pelvic fixation, lumbosacral TLIF results in increased ROM at the proximal junction while ALIF does not. Further augmentation of either ALIF or TLIF constructs with lumbosacral accessory rods does not impact proximal junctional ROM. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.