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Direct Lateral Approach to Lumbar Fusion Is a Biomechanically Equivalent Alternative to the Anterior Approach: An In Vitro Study

Laws, Cory J. BS*; Coughlin, Dezba G. PhD*; Lotz, Jeffrey C. PhD*; Serhan, Hassan A. PhD; Hu, Serena S. MD*

doi: 10.1097/BRS.0b013e31823551aa
Biomechanics

Study Design. A human cadaveric biomechanical study of lumbar mobility before and after fusion and with or without supplemental instrumentation for 5 instrumentation configurations.

Objective. To determine the biomechanical differences between anterior lumbar interbody fusion (ALIF) and direct lateral interbody fusion (DLIF) with and without supplementary instrumentation.

Summary of Background Data. Some prior studies have compared various surgical approaches using the same interbody device whereas others have investigated the stabilizing effect of supplemental instrumentation. No published studies have performed a side-by-side comparison of standard and minimally invasive techniques with and without supplemental instrumentation.

Methods. Eight human lumbosacral specimens (16 motion segments) were tested in each of the 5 following configurations: (1) intact, (2) with ALIF or DLIF cage, (3) with cage plus stabilizing plate, (4) with cage plus unilateral pedicle screw fixation (PSF), and (5) with cage plus bilateral PSF. Pure moments were applied to induce specimen flexion, extension, lateral bending, and axial rotation. Three-dimensional kinematic responses were measured and used to calculate range of motion, stiffness, and neutral zone.

Results. Compared to the intact state, DLIF significantly reduced range of motion in flexion, extension, and lateral bending (P = 0.0117, P = 0.0015, P = 0.0031). Supplemental instrumentation significantly increased fused-specimen stiffness for both DLIF and ALIF groups. For the ALIF group, bilateral PSF increased stiffness relative to stand-alone cage by 455% in flexion and 317% in lateral bending (P = 0.0009 and P < 0.0001). The plate increased ALIF group stiffness by 211% in extension and 256% in axial rotation (P = 0.0467 and P = 0.0303). For the DLIF group, bilateral PSF increased stiffness by 350% in flexion and 222% in extension (P < 0.0001 and P = 0.0008). No differences were observed between ALIF and DLIF groups supplemented with bilateral PSF.

Conclusion. Our data support that the direct lateral approach, when supplemented with bilateral PSF, is a minimally invasive and biomechanically stable alternative to the open, anterior approach to lumbar spine fusion.

An in vitro biomechanical evaluation of 2 approaches to lumbar fusion is presented. For each approach, the additional effect of supplemental instrumentation is investigated. Data imply that the direct lateral approach, when supplemented with bilateral pedicle screw fixation, is a minimally invasive and biomechanically equivalent alternative to the anterior approach.

*University of California, San Francisco

DePuy Spine, Rayhman, MA.

Address correspondence and reprint requests to Jeffrey C. Lotz, PhD, 513 Parnassus Ave, S1157, University of California, San Francisco, CA 94143; E-mail: lotzj@orthosurg.ucsf.edu

Acknowledgment date: March 17, 2011. First revision date: July 1, 2011. Second revision date: August 25, 2011. Acceptance date: August 27, 2011.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

Corporate/Industry funds were received in support of this work. Although one or more of the author(s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript, benefits will be directed solely to a research fund, foundation, educational institution, or other nonprofit organization with which the author(s) has/have been associated.

© 2012 Lippincott Williams & Wilkins, Inc.