title: Multidirectional flexibility of the spine following posterior decompressive surgery after single-level cervical disc arthroplasty: an in vitro biomechanical investigation.
abstract: METHODS
  In vitro human cadaveric biomechanical study.
  
  
  OBJECTIVE
  This study quantifies the multidirectional flexibility of the spine following laminoplasty and laminectomy after cervical disc arthroplasty.
  
  
  BACKGROUND
  Posterior decompressive surgery may be used to treat recurrence of myeloradiculopathy following disc arthroplasty. This is the first study investigating the biomechanical effects of posterior decompressive surgery combined with cervical disc arthroplasty.
  
  
  METHODS
  Seven human cervical spines were biomechanically evaluated under the following conditions: (1) intact; (2) discectomy (C5-C6); (3) disc arthroplasty (C5-C6); (4) arthroplasty + 3-level laminoplasty (C3-C5); (5) arthroplasty + 4-level laminoplasty (C3-C6); (6) arthroplasty + 5-level laminoplasty (C3-C7); (7) arthroplasty + 5-level laminoplasty (C3-C7) without hydroxyapatite spacers; and (8) arthroplasty + laminectomy (C3-C7). Multidirectional flexibility testing used unconstrained pure moments of ±2 Nm for flexion-extension, axial rotation, and lateral bending. Quantification of C5-C6 and C3-C7 range of motion (ROM) and neutral zone (NZ) were normalized to the intact spine (100%).
  
  
  RESULTS
  Flexion-extension loading of the discectomy condition demonstrated ROM of 22.05° ± 4.17° at the operative level (P < 0.05). Implantation of the porous coated motion device restored segmental motion near the intact condition (ROM, 9.97° ± 6.44°; NZ, 5.82° ± 6.18°). There were no statistical differences between 3-level (13.79° ± 6.49°), 4-level (14.51° ± 5.76°), and 5-level (15.67° ± 5.71°) laminoplasty; however, additional levels demonstrated a trend toward increased motion at the arthroplasty level. Laminoplasty without spacers (17.45°) and laminectomy (18.27°) indicated even greater segmental motion (P > 0.05). Axial rotation and lateral bending indicated trends similar to those for flexion-extension.
  
  
  CONCLUSIONS
  Posterior decompressive surgery increased ROM and NZ in all loading modes compared to arthroplasty alone, and laminectomy markedly increased motion compared with laminoplasty. Use of hydroxyapatite spacers and minimization of the extent of laminoplasty appear to be biomechanically favorable in this in vitro model.
authors.affiliation: Orthopaedic Spinal Research Laboratory, St Joseph Medical Center, Towson, MD 21204, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Kikkawa
authors.forename: Bryan W
authors.initials: BW
authors.lastname: Cunningham
authors.forename: Osamu
authors.initials: O
authors.lastname: Shirado
authors.forename: Nianbin
authors.initials: N
authors.lastname: Hu
authors.forename: Paul C
authors.initials: PC
authors.lastname: McAfee
authors.forename: Hiromi
authors.initials: H
authors.lastname: Oda
mesh_terms: D019643:Arthroplasty, Replacement; D001696:Biomechanical Phenomena; D002574:Cervical Vertebrae / Q000601:surgery; D019299:Decompression, Surgical; D017586:Diskectomy; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology*; D013131:Spine / Q000502:physiology* / Q000601:surgery*