title: Feasibility and biomechanical performance of a novel transdiscal screw system for one level in non-spondylolisthetic lumbar fusion: an in vitro investigation.
abstract: BACKGROUND
  The bilateral pedicle screw system (BPSS) is currently the "gold standard" fusion technique for spinal instability. A new stabilization system that provides the same level of stability through a less invasive procedure will have a high impact on clinical practice. A new transdiscal screw system is investigated as a promising minimally invasive device.
  
  
  OBJECTIVE
  To evaluate the feasibility of a novel transdiscal screw in spinal fixation as an alternative to BPSS, with and without an interbody cage, in non-spondylolisthesis cases.
  
  
  METHODS
  An in vitro biomechanical study in lumbar cadaveric spines.
  
  
  METHODS
  Twelve lumbar cadaveric segments (L4-S1) were tested under flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Six treatments were simulated as follows: (1) intact, (2) bilateral facetectomy at L4-L5, (3) transdiscal screw system, (4) BPSS, (5) BPSS with transforaminal lumbar interbody cage, and (6) transdiscal screws with transforaminal interbody cage. Specimens were randomly divided into two testing groups: Group 1 (n=6) was tested under the first five conditions, in the order presented, whereas Group 2 (n=6) was tested under the first, second, third, fourth, and sixth conditions, with the fourth condition preceding the third. Range of motion (ROM) and neutral zone stiffness (NZS) were estimated and normalized with respect to the intact condition to explore statistical differences among treatments using non-parametric approaches.
  
  
  RESULTS
  Significant differences in FE ROM were observed in the pedicle screws-cage condition with respect to the facetectomy (p<.01), the pedicle screw (p=.03), and the transdiscal screw (p<.02) conditions. All fixation constructs significantly restricted LB and AR ROM (p<.01) with respect to facetectomy. In terms of stiffness, the pedicle screw and the transdiscal screw systems increased (p<.01) LB and AR NZS with respect to facetectomy. The pedicle screws-cage condition significantly increased flexion and extension stiffness with respect to all other conditions (p<.05). However, LB NZS for the pedicle screws-cage and the transdiscal screws-cage condition could not be explored due to a testing order bias effect. There was not enough evidence to state any difference between the pedicle and transdiscal screw conditions in terms of ROM or NZS.
  
  
  CONCLUSIONS
  Transdiscal and pedicle screw systems showed comparable in vitro biomechanical performance in the immediate stabilization of a complete bilateral facetectomy. The pedicle screws-cage condition was the most stable in FE motion; however, comparison with respect to the transdiscal screws-cage condition could not be investigated.
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program, 12902 Magnolia Dr, Tampa, FL 33612, USA; Department of Neurosurgery and Orthopedics, College of Medicine, University of South Florida, 12901 Bruce B Downs Blvd, Tampa, FL 33612, USA. Electronic address: kamran.aghayev@moffitt.org.
authors.forename: Kamran
authors.initials: K
authors.lastname: Aghayev
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program, 12902 Magnolia Dr, Tampa, FL 33612, USA.
authors.forename: Sabrina A
authors.initials: SA
authors.lastname: Gonzalez-Blohm
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program, 12902 Magnolia Dr, Tampa, FL 33612, USA; Department of Mechanical Engineering, University of South Florida, 4202 East Fowler Ave, Tampa, FL 33620, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Doulgeris
authors.affiliation: Department of Chemical & Biomedical Engineering, University of South Florida, 4202 East Fowler Ave, Tampa, FL 33620, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Lee
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program, 12902 Magnolia Dr, Tampa, FL 33612, USA; Department of Neurosurgery and Orthopedics, College of Medicine, University of South Florida, 12901 Bruce B Downs Blvd, Tampa, FL 33612, USA.
authors.forename: Jason K
authors.initials: JK
authors.lastname: Waddell
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, NeuroOncology Program, 12902 Magnolia Dr, Tampa, FL 33612, USA; Department of Neurosurgery and Orthopedics, College of Medicine, University of South Florida, 12901 Bruce B Downs Blvd, Tampa, FL 33612, USA.
authors.forename: Frank D
authors.initials: FD
authors.lastname: Vrionis
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D005240:Feasibility Studies; D006801:Humans; D016268:Internal Fixators; D007593:Joint Instability / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods
keywords: Complete bilateral facetectomy; Minimally invasive; Neutral zone stiffness; Range of motion; Transdiscal fusion