Biomechanical comparison of an interspinous fusion device and bilateral pedicle screw system as additional fixation for lateral lumbar interbody fusion James J. Doulgeris a,b, ⁎, Kamran Aghayev a , Sabrina A. Gonzalez-Blohm a , William E. Lee III c , Frank D. Vrionis a a H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program and Department of Neurosurgery and Orthopedics, University of South Florida, College of Medicine, Tampa, FL 33612, USA b Dept of Mechanical Engineering, University of South Florida, Tampa, FL 33620, USA c Dept of Chemical & Biomedical Engineering, University of South Florida, Tampa, FL 33620, USA abstract article info Article history: Received 5 June 2014 Accepted 8 October 2014 Keywords: Lumbar spine Posterior fixation Biomechanics Range of motion Stiffness Background: This investigation compares an interspinous fusion device with posterior pedicle screw system in a lateral lumbar interbody lumbar fusion. Methods: We biomechanically tested six cadaveric lumbar segments (L1–L2) under an axial preload of 50 N and torque of 5 Nm in flexion–extension, lateral bending and axial rotation directions. We quantified range of motion, neutral zone/elastic zone stiffness in the following conditions: intact, lateral discectomy, lateral cage, cage with interspinous fusion, and cage with pedicle screws. Findings: A complete lateral discectomy and annulectomy increased motion in all directions compared to all other conditions. The lateral cage reduced motion in lateral bending and flexion/extension with respect to the intact and discectomy conditions, but had minimal effect on extension stiffness. Posterior instrumentation reduced mo- tion, excluding interspinous augmentation in axial rotation with respect to the cage condition. Interspinous fu- sion significantly increased flexion and extension stiffness, while pedicle screws increased flexion/extension and lateral bending stiffness, with respect to the cage condition. Both posterior augmentations performed equiv- alently throughout the tests except in lateral bending stiffness where pedicle screws were stiffer in the neutral zone. Interpretation: A lateral discectomy and annulectomy generates immediate instability. Stand-alone lateral cages restore a limited amount of immediate stability, but posterior supplemental fixation increases stability. Both augmentations are similar in a single level lateral fusion in-vitro model, but pedicle screws are more equipped for coronal stability. An interspinous fusion is a less invasive alternative than pedicle screws and is potentially a conservative option for various interbody cage scenarios. © 2014 Published by Elsevier Ltd. 1. Introduction Interbody fusion has become a common practice in spine surgery. Among different surgical interbody fusion techniques, the transpsoas approach or lateral lumbar interbody fusion (LLIF) has gradually gained popularity during the last decade (Isaacs et al., 1976; Le Huec et al., 2002; Ozgur et al., 2006; Rodgers et al., 2010; Simpson et al., 2011). The LLIF involves a minimally invasive retroperitoneal transpsoas ap- proach that makes it an attractive option. Unlike anterior and posterior approaches, risk of major vessel injury (Ozgur et al., 2006) and neuro- logical complications (Simpson et al., 2011) are reduced in a LLIF proce- dure. Nevertheless, a common clinical question is whether to implant a LLIF as stand-alone instrumentation or augment the cage with posterior instrumentation. Bilateral pedicle screw stabilization (BPSS) is currently considered the “gold standard” in posterior lumbar stabilization (Isaacs et al., 1976; Slucky et al., 2006), but this all-encompassing technique comes at costs of invasiveness, surgical time, radiation exposure, risk of pedicle screw breach and potential nerve root injury (Kaibara et al., 2010; Karahalios et al., 2010). These complications can prevent surgeons from supporting anterior hardware, so developing minimally invasive procedures, testing alternative devices, reducing complications of actual procedures, and proposing new treatments that provide similar stabili- zation to BPSS are of interest in spine research. A LLIF cage is implanted while the patient is in a lateral decubitus position (Ozgur et al., 2006). Implantation of percutaneous pedicle screws requires patient manipulation to a prone position (Ozgur et al., 2006) with two lateral incisions. Conversely, surgeons can implant an Clinical Biomechanics 30 (2015) 205–210 ⁎ Corresponding author at: H. Lee Moffitt Cancer Center, 12902 Magnolia Drive, Tampa, FL 33612, USA. E-mail address: James.Doulgeris@moffitt.org (J.J. Doulgeris). http://dx.doi.org/10.1016/j.clinbiomech.2014.10.003 0268-0033/© 2014 Published by Elsevier Ltd. Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech