title: Use of Supplemental Short Pre-Contoured Accessory Rods and Cobalt Chrome Alloy Posterior Rods Reduces Primary Rod Strain and Range of Motion Across the Pedicle Subtraction Osteotomy Level: An In Vitro Biomechanical Study.
abstract: METHODS
  In vitro cadaveric biomechanical study.
  
  
  OBJECTIVE
  To assess effects of 4-rod reconstruction, rod material, and anterior column support on motion and surface rod strain in a pedicle subtraction osteotomy model.
  
  
  BACKGROUND
  Pedicle subtraction osteotomy (PSO) can correct significant sagittal deformity of the lumbar spine; however, revision rates are high. To reduce rod strain and the incidence of rod fracture, clinical use of multi-rod construction, cobalt chrome (CoCr) alloy rods, and interbody spacers adjacent to PSO has been proposed. Investigating both motion and rod strain is necessary to determine the biomechanical efficacy of these techniques.
  
  
  METHODS
  Five specimens (T12-S1) underwent PSO at L3 with pedicle screw stabilization at L1-S1. Pedicle subtraction was adjusted to achieve a final lordosis of 70°. Flexion-extension (FE), lateral bending, and axial rotation were applied. Linear strain gauges measured surface rod strain during FE on primary and accessory rods at PSO level. Testing evaluated (1) accessory rods (4-Rod) added at PSO level versus primary rods (2-Rod); (2) Ti versus CoCr rods; and (3) lateral interbody spacers (S) inserted adjacent to PSO. One-way and three-way analysis of variance was performed (P ≤ 0.05).
  
  
  RESULTS
  All constructs significantly reduced FE and lateral bending motion relative to intact (P < 0.001). The main effect of accessory rods in reducing FE motion was significant (P = 0.021). Accessory and CoCr rods reduced relative surface strain on the primary rod, irrespective of construct (P < 0.001). CoCr 4-Rod + S provided the greatest reduction in strain (76% decrease; P = 0.003).
  
  
  CONCLUSIONS
  Accessory and CoCr rods provided greatest reduction in motion and rod strain at PSO level. Interbody devices minimally affected motion-induced strain and might act primarily to maintain disc height. Clinicians must assess whether surface strain and motion reduction minimize the incidence of rod fracture.
  
  
  METHODS
  N/A.
authors.affiliation: *Department of Orthopaedic Surgery, Copenhagen University Hospital, Copenhagen, Denmark†Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA‡Department of Spinal Surgery, 2nd Affiliated Hospital of Wenzhou Medical University, Wenzhou, China.
authors.forename: Dennis Winge
authors.initials: DW
authors.lastname: Hallager
authors.forename: Martin
authors.initials: M
authors.lastname: Gehrchen
authors.forename: Benny
authors.initials: B
authors.lastname: Dahl
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Harris
authors.forename: Manasa
authors.initials: M
authors.lastname: Gudipally
authors.forename: Sean
authors.initials: S
authors.lastname: Jenkins
authors.forename: Ai-Min
authors.initials: AM
authors.lastname: Wu
authors.forename: Brandon S
authors.initials: BS
authors.lastname: Bucklen
mesh_terms: D001696:Biomechanical Phenomena; D002858:Chromium Alloys / Q000627:therapeutic use*; D006801:Humans; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery*; D008954:Models, Biological; D010027:Osteotomy / Q000295:instrumentation*; D016059:Range of Motion, Articular / Q000502:physiology*; D013123:Spinal Fusion / Q000295:instrumentation*
chemical_list: D002858:Chromium Alloys