title: Direct lateral approach to lumbar fusion is a biomechanically equivalent alternative to the anterior approach: an in vitro study.
abstract: METHODS
  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.
  
  
  BACKGROUND
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: University of California, San Francisco 94143, USA.
authors.forename: Cory J
authors.initials: CJ
authors.lastname: Laws
authors.forename: Dezba G
authors.initials: DG
authors.lastname: Coughlin
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Lotz
authors.forename: Hassan A
authors.initials: HA
authors.lastname: Serhan
authors.forename: Serena S
authors.initials: SS
authors.lastname: Hu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000473:pathology / Q000502:physiology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation / Q000379:methods*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*