title: A Biomechanical Comparison of Shape Design and Positioning of Transforaminal Lumbar Interbody Fusion Cages.
abstract: METHODS
  Cadaveric biomechanical analysis.
  
  
  OBJECTIVE
  The aim of this study was to compare three interbody cage shapes and their position within the interbody space with regards to construct stability for transforaminal lumbar interbody fusion.
  
  
  METHODS
  Twenty L2-L3 and L4-L5 lumbar motion segments from fresh cadavers were potted in polymethyl methacrylate and subjected to testing with a materials testing machine before and after unilateral facetectomy, diskectomy, and interbody cage insertion. The three cage types were kidney-shaped, articulated, and straight bullet-shaped. Each cage type was placed in a common anatomic area within the interbody space before testing: kidney, center; kidney, anterior; articulated, center; articulated, anterior; bullet, center; bullet, lateral. Load-deformation curves were generated for axial compression, flexion, extension, right bending, left bending, right torsion, and left torsion. Finally, load to failure was tested.
  
  
  RESULTS
  For all applied loads, there was a statistically significant decrease in the slope of the load-displacement curves for instrumented specimens compared with the intact state (p < 0.05) with the exception of right axial torsion (p = 0.062). Among all instrumented groups, there was no statistically significant difference in stiffness for any of the loading conditions or load to failure.
  
  
  CONCLUSIONS
  Our results failed to show a clearly superior cage shape design or location within the interbody space for use in transforaminal lumbar interbody fusion.
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Redwood City, California, United States.
authors.forename: Garet C
authors.initials: GC
authors.lastname: Comer
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Redwood City, California, United States.
authors.forename: Anthony
authors.initials: A
authors.lastname: Behn
authors.affiliation: University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States.
authors.forename: Shashank
authors.initials: S
authors.lastname: Ravi
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Redwood City, California, United States.
authors.forename: Ivan
authors.initials: I
authors.lastname: Cheng
keywords: biomechanics; interbody cage; lumbar fusion; lumbar spine; spinal instrumentation; transforaminal lumbar interbody fusion