title: MIS Expandable Interbody Spacers: A Literature Review and Biomechanical Comparison of an Expandable MIS TLIF With Conventional TLIF and ALIF.
abstract: METHODS
  Biomechanical study and review of literature on expandable lumbar interbody fusion constructs.
  
  
  OBJECTIVE
  To evaluate the biomechanical stability of expandable interbody devices.
  
  
  BACKGROUND
  Lumbar interbody implants placed from an anterior or lateral approach are desirable due to their large size, providing a stable fusion environment. Posterior implants are typically limited by their access corridor. Expandable footprint transforaminal lumbar interbody fusion (TLIF) interbodies may allow for a minimally invasive TLIF approach with the biomechanical benefits of an anterior lumbar interbody fusion (ALIF)-sized graft; however, this requires experimental investigation.
  
  
  METHODS
  Six cadaveric L1-sacrum segments were tested intact with pure moments of  ± 7.5  N m in flexion-extension, lateral bending, and axial rotation. Specimens received at L4-5 either a medial-lateral expandable TLIF cage (MLX-TLIF) or a conventional polyether ether ketone (PEEK) banana-shaped TLIF cage (Conv-TLIF) first. Both were tested with unilateral and bilateral pedicle screw (PS) fixation. Testing was repeated with the alternate cage and fixation. Motion marker arrays were fixed to L4 and L5 to assess range of motion. Results were compared with published data for a PEEK ALIF cage with anterior plate and a PEEK ALIF cage with bilateral PS fixation, tested under the same conditions.
  
  
  RESULTS
  The most rigid construct was ALIF with bilateral PS fixation in flexion-extension and axial rotation, whereas MLX with bilateral PS was most rigid in lateral bending. Conv-TLIF with unilateral PS was the least rigid construct. MLX-TLIF with unilateral PS provided similar range of motion to Conv-TLIF with bilateral PS in flexion-extension and lateral bending, and ALIF with anterior plate in lateral bending.
  
  
  CONCLUSIONS
  The MLX-TLIF cage with unilateral PS fixation provided comparable stability to conventional TLIF with bilateral PS fixation and ALIF with anterior plate treatments. The large footprint of the expandable cage may reduce the TLIF supplemental fixation demands and facilitate minimally invasive single-position surgery. If needed, additional stability may be achieved by using bilateral PS.
  
  
  METHODS
  N/A.
authors.affiliation: *Lyerly Neurosurgery, Jacksonville, FL †Southern Oregon Spine Care, Medford, OR ‡St Vincent's Brain and Spine Institute, Jacksonville, FL §Roush Spine, Lake Worth, FL ¶Augusta Orthopedic and Sports Medicine Specialist, PC, Augusta, GA ||NuVasive, Inc., San Diego, CA.
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Cannestra
authors.forename: Mark D
authors.initials: MD
authors.lastname: Peterson
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Parker
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Roush
authors.forename: Justin V
authors.initials: JV
authors.lastname: Bundy
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Turner
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004867:Equipment Design; D006801:Humans; D008159:Lumbar Vertebrae / Q000601:surgery*; D008161:Lumbosacral Region / Q000601:surgery*; D008875:Middle Aged; D065289:Pedicle Screws; D019736:Prostheses and Implants; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation*; D055815:Young Adult