title: Biomechanical assessment of unilateral pedicle screws plus contralateral transfacetopedicular screws after transforaminal lumbar interbody fusion with two cages.
abstract: OBJECTIVE
  To assess the biomechanical stability of unilateral pedicle screws (UPS) plus contralateral transfacetopedicular screws (TFPS) after transforaminal lumbar interbody fusion (TLIF) with two cages.
  
  
  METHODS
  Range of motion (ROM) testing was performed in 28 fresh-frozen human cadaveric lumbar spine motion segments. The sequential test configurations included supplemental constructs after TLIF such as UPS, UPS plus contralateral TFPS and bilateral pedicle screws (BPS). All test specimens were fixated in the normal lordotic lignment, then mounted in a three-dimensional (3-D) motion testing machine and fixed to the load frame of a six degrees of freedom spine simulator. Each of the test constructs were subjected to three load-unload cycles in each of the physiologic planes generating flexion-extension, right-left lateral bending and right-left axial rotation load-displacement curves. Statistical analysis was performed on the ROM data. Comparison of data was performed by repeated-measures analysis of variance for independent samples followed by Bonferroni analysis for multiple comparison procedures.
  
  
  RESULTS
  The ROMs for UPS, BPS and UPS plus TFPS fixation after TLIF were significantly smaller than those of the intact spine in all modes. The ROM for UPS plus TFPS fixation was between the largest for UPS and the smallest for BPS. The differences between ROMs of UPS and UPS plus TFPS were significant for both lateral bending and rotation. There were no significant differences between BPS and UPS plus TFPS in any mode.
  
  
  CONCLUSIONS
  Because the UPS construct provides the least stability, especially during lateral bending and rotation, it should be used prudently. After TLIF with two cages, UPS plus TFPS provides stability comparable to that of TLIF with BPS. It is thus an acceptable option in minimally invasive surgery.
authors.affiliation: Department of Orthopaedics, Jiangmen Central Hospital of Guangdong Province, Jiangmen, China.
authors.forename: Zhong-Lin
authors.initials: ZL
authors.lastname: Xue
authors.forename: Zhong-Xian
authors.initials: ZX
authors.lastname: Chen
authors.forename: Chao-Hua
authors.initials: CH
authors.lastname: Fu
authors.forename: Hong-Jun
authors.initials: HJ
authors.lastname: Lei
authors.forename: Xiang-Wei
authors.initials: XW
authors.lastname: Yuan
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D001863:Bone Screws; D002102:Cadaver; D006801:Humans; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000503:physiopathology / Q000601:surgery*; D008422:Materials Testing / Q000379:methods; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D055815:Young Adult
keywords: Biomechanical assessment; Pedicle screws; Transfacetopedicular screw; Transforaminal lumbar interbody fusion