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Global Spine J. 2018 Sep;8(6):607-614. doi: 10.1177/2192568218759037. Epub 2018 Mar 20.

Biomechanics of L5/S1 in Long Thoracolumbosacral Constructs: A Cadaveric Study.

Author information

Cleveland Clinic, Cleveland, OH, USA.
Bryan S. Lee and Kevin M. Walsh are co-first authors.
Allegheny Health Network, Pittsburgh, PA, USA.
Carolina Neurosurgery and Spine Associates, Charlotte, NC, USA.


Study Design:

In vitro cadaveric biomechanical study.


Despite numerous techniques employed to establish solid lumbosacral fixation, there are little biomechanical data correlating fixation methods at L5/S1 to thoracolumbosacral (TLS) construct length. We aimed to determine the optimal construct with the hypothesis that under physiological loads, lumbosacral constructs can be stabilized by L5/S1 anterior lumbar interbody fusion (ALIF) alone, without iliac screw fixation (ISF), and that TLS constructs would require ISF, with or without ALIF.


By using a robot capable of motion in 6 axes, force-moment sensor, motion-tracking camera system and software, we simulated the spinal loading effects in flexion-extension, axial rotation, and lateral bending, and compared torques in different construct groups of T4-S1, T10-S1, and L2-S1. By conducting multidirectional flexibility testing we assessed the effects of constructs of various lengths on the L5/S1 segment.


L2-S1 constructs may be equivalently stabilized by L5/S1 ALIF alone without ISF. Longer TLS constructs exerted increasing motion at L5/S1, exhibiting trends in favor of ISF when extending to T10 and statistically improved fixation when extending to T4. Lastly, TLS constructs with ISF exhibited a statistically significant reduction in L5-S1 range of motion from the addition of ALIF when extending to T4-pelvis but not T10-pelvis.


We found that ALIF alone may sufficiently support the L2-S1 construct, reducing L5/S1 range of motion and transmitting loads instead to the sacropelvis. Furthermore, ALIF was found to add significant stability to the T4-pelvis construct when added to ISF. This difference was not significant for the T10-pelvis construct.


ALIF; anterior lumbar interbody fusion; biomechanics; iliac screw fixation; lumbosacral fixation; sacroiliac fixation

Conflict of interest statement

Declaration of Conflicting Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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