title: Biomechanical analysis of an expandable lateral cage and a static transforaminal lumbar interbody fusion cage with posterior instrumentation in an in vitro spondylolisthesis model.
abstract: OBJECTIVE
  Insufficient biomechanical data exist from comparisons of the stability of expandable lateral cages with that of static transforaminal lumbar interbody fusion (TLIF) cages. The purpose of this biomechanical study was to compare the relative rigidity of L4-5 expandable lateral interbody constructs with or without additive pedicle screw fixation with that of L4-5 static TLIF cages in a novel cadaveric spondylolisthesis model.
  
  
  METHODS
  Eight human cadaver spines were used in this study. A spondylolisthesis model was created at the L4-5 level by creating 2 injuries. First, in each cadaver, a nucleotomy from 2 channels through the anterior side was created. Second, the cartilage of the facet joint was burred down to create a gap of 4 mm. Light-emitting-diode tracking markers were placed at L-3, L-4, L-5, and S-1. Specimens were tested in the following scenarios: intact model, bilateral pedicle screws, expandable lateral 18-mm-wide cage (alone, with unilateral pedicle screws [UPSs], and with bilateral pedicle screws [BPSs]), expandable lateral 22-mm-wide cage (alone, with UPSs, and with BPSs), and TLIF (alone, with UPSs, and with BPSs). Four of the spines were tested with the expandable lateral cages (18-mm cage followed by the 22-mm cage), and 4 of the spines were tested with the TLIF construct. All these constructs were tested in flexion-extension, axial rotation, and lateral bending.
  
  
  RESULTS
  The TLIF-alone construct was significantly less stable than the 18- and 22-mm-wide lateral lumbar interbody fusion (LLIF) constructs and the TLIF constructs with either UPSs or BPSs. The LLIF constructs alone were significantly less stable than the TLIF construct with BPSs. However, there was no significant difference between the 18-mm LLIF construct with UPSs and the TLIF construct with BPSs in any of the loading modes.
  
  
  CONCLUSIONS
  Expandable lateral cages with UPSs provide stability equivalent to that of a TLIF construct with BPSs in a degenerative spondylolisthesis model.
authors.affiliation: Department of Orthopaedic Surgery, George Washington University, Washington, DC; and.
authors.forename: Matthew
authors.initials: M
authors.lastname: Mantell
authors.affiliation: Department of Orthopaedic Surgery, George Washington University, Washington, DC; and.
authors.forename: Mathew
authors.initials: M
authors.lastname: Cyriac
authors.affiliation: Department of Orthopaedic Surgery, George Washington University, Washington, DC; and.
authors.forename: Colin M
authors.initials: CM
authors.lastname: Haines
authors.affiliation: Globus Medical, Audubon, Pennsylvania.
authors.forename: Manasa
authors.initials: M
authors.lastname: Gudipally
authors.affiliation: Department of Orthopaedic Surgery, George Washington University, Washington, DC; and.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: O'Brien
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology*; D002102:Cadaver; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000601:surgery*; D008161:Lumbosacral Region / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D016059:Range of Motion, Articular / Q000502:physiology*; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods; D013168:Spondylolisthesis / Q000601:surgery*
keywords: BPS = bilateral pedicle screw; CLn = n-mm Caliber-L cage; HSD = Tukey’s honest significant difference; LLIF = lateral lumbar interbody fusion; LLIFn = n-mm LLIF cage; ROM = range of motion; TLIF = transforaminal lumbar interbody fusion; UPS = unilateral pedicle screw; biomechanical; lateral lumbar interbody fusion; pedicle screw; transforaminal lumbar interbody fusion