title: Construct stability of an instrumented 2-level cervical corpectomy model following fatigue testing: biomechanical comparison of circumferential antero-posterior instrumentation versus a novel anterior-only transpedicular screw-plate fixation technique.
abstract: BACKGROUND
  A high rate of complications in multilevel cervical surgery with corpectomies and anterior-only screw-and-plate stabilization is reported. A 360°-instrumentation improves construct stiffness and fusion rates, but adds the morbidity of a second approach. A novel ATS-technique (technique that used anterior transpedicular screw placement) was recently described, yet no study to date has analyzed its performance after fatigue loading. Accordingly, the authors performed an analysis of construct stiffness after fatigue testing of a cervical 2-level corpectomy model reconstructed using a novel anterior transpedicular screw-and-plate technique (ATS-group) in comparison to standard antero-posterior instrumentation (360°-group).
  
  
  METHODS
  Twelve fresh-frozen human cervical spines were mounted on a spine motion tester to analyze restriction of ROM under loading (1.5 Nm) in flexion-extension (FE), axial rotation (AR), and lateral bending (LB). Testing was performed in the intact state, and after instrumentation of a 2-level corpectomy C4 + C5 using a cage and the constructs of ATS- and 360°-group, after 1,000 cycles, and after 2,000 cycles of fatigue testing. In the ATS-group (n = 6), instrumentation was achieved using a customized C3-C6 ATS-plate system. In the 360°-group (n = 6), instrumentation consisted of a standard anterior screw-and-plate system with a posterior instrumentation using C3-C6 lateral mass screws. Motion data were assessed as degrees and further processed as normalized values after standardization to the intact ROM state.
  
  
  RESULTS
  Specimen age and BMD were not significantly different between the ATS- and 360°-groups. After instrumentation and 2,000 cycles of testing, no specimen exhibited a ROM greater than in the intact state. No specimen exhibited catastrophic construct failure after 2,000 cycles. Construct stiffness in the 360°-group was significantly increased compared to the ATS-group for all loading conditions, except for FE-testing after instrumentation. After 2,000 cycles, restriction of ROM under loading in FE was 39.8 ± 30% in the ATS-group vs. 2.8 ± 2.3% in the 360°-group, in AR 60.4 ± 25.8 vs 15 ± 11%, and in LB 40 ± 23.4 vs 3.9 ± 1.2%. Differences were significant (p < 0.05).
  
  
  CONCLUSIONS
  360°-instrumentation resembles the biomechanical standard of reference for stabilization of 2-level corpectomies. An ATS-construct was also shown to confer high construct stiffness, significantly reducing the percentage ROM beyond that of an intact specimen after 2,000 cycles. This type of instrumentation might be a clinical valuable and biomechanically sound adjunct to multilevel anterior surgical procedures.
authors.affiliation: German Scoliosis Center Bad Wildungen, Werner-Wicker-Klinik, Im Kreuzfeld 4, 34537, Bad Wildungen, Germany. heiko.koller@t-online.de.|Department for Traumatology and Sports Injuries, Paracelsus Medical University, Salzburg, Austria. heiko.koller@t-online.de.
authors.forename: Heiko
authors.initials: H
authors.lastname: Koller
authors.affiliation: Department of Trauma Surgery, Medical University Innsbruck, Innsbruck, Austria.
authors.forename: Werner
authors.initials: W
authors.lastname: Schmoelz
authors.affiliation: Department for Traumatology and Orthopedic Surgery, Stadtkrankenhaus Korbach, Korbach, Germany.
authors.forename: Juliane
authors.initials: J
authors.lastname: Zenner
authors.affiliation: Department for Traumatology and Sports Injuries, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Alexander
authors.initials: A
authors.lastname: Auffarth
authors.affiliation: Department for Traumatology and Sports Injuries, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Herbert
authors.initials: H
authors.lastname: Resch
authors.affiliation: Research Office, Biostatistics, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hitzl
authors.affiliation: Department of Trauma Surgery, Medical University Innsbruck, Innsbruck, Austria.
authors.forename: Davud
authors.initials: D
authors.lastname: Malekzadeh
authors.affiliation: Department for Traumatology and Sports Injuries, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Lukas
authors.initials: L
authors.lastname: Ernstbrunner
authors.affiliation: Department for Traumatology and Sports Injuries, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Martina
authors.initials: M
authors.lastname: Blocher
authors.affiliation: German Scoliosis Center Bad Wildungen, Werner-Wicker-Klinik, Im Kreuzfeld 4, 34537, Bad Wildungen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Mayer
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D019299:Decompression, Surgical / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D008297:Male; D008422:Materials Testing; D008875:Middle Aged
keywords: 360° instrumentation; Anterior transpedicular; Biomechanical testing; Cervical spine; Corpectomy; Cyclic loading