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  • A Biomechanical Study of OLIF with Unilateral and Bilateral Fixation

    Final Number:

    Kirk McGilvray (1) PhD; Hal MD Silcox MD (2); Jeremy Rawlinson PhD (3); Christian M. Puttlitz PhD (1)

    Study Design:
    Laboratory Investigation

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2017 Annual Meeting

    Introduction: Oblique lumbar interbody fusion (OLIF) is an anterolateral approach for lumbar intervertebral fusion that avoids trans-psoas surgery and the attendant risks of muscular and neurologic injury. There remain questions as to the degree of adjunctive fixation required, if any, to achieve acute stability with anterior and/or posterior fixation options. The objective of this study was to determine the contribution of unilateral or bilateral rod fixation to the acute stability obtained with cages inserted using an OLIF approach to the lumbar spine.

    Methods: Six lumbar (L1-L5) spine sections were utilized in this project. The spines were tested in their intact condition using a standard kinetic protocol. Cages were placed in the L3-L4 intervertebral space and tested: (1) as is, (2) with bilateral pedicle screws and rods, (3) with bilateral pedicle screws and rods and a 2 hole plate (obliquely placed), or (4) with ipsilateral unilateral pedicle screws and rods and a 2 hole plate (obliquely placed), and (5) with contralateral unilateral pedicle screws and rods and a 2 hole plate (obliquely placed).

    Results: All of the instrumented spines demonstrated significantly (p<0.03) reduced flexion-extension, axial rotation and lateral bending ROM as compared to the intact case. The flexion-extension and lateral bending ROM with the bilateral pedicle screw and rod construct (with or without a plate) was significantly reduced (p<0.04) as compared to the cage alone as well as the two unilateral pedicle screw and rod constructs, however these differences were all less than 1 degree. The cage alone demonstrated significantly (p<0.01) greater axial rotation ROM as compared to all the other fixation scenarios.

    Conclusions: The data indicate that unilateral pedicle screws and rod with oblique plate fixation closely approximates bilateral pedicle screw hardware as an adjunctive fixation for cages inserted with an OLIF approach.

    Patient Care: This study compares the biomechanics of rod fixation for surgeons to consider with minimally-invasive approaches for patients undergoing interbody fusion.

    Learning Objectives: By the conclusion of this session, participants should be able to identify the effects of OLIF fixation with unilateral and bilateral fixation.


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