title: Cortical bone facet spacers for cervical spine decompression: effects on intervertebral kinetics and foraminal area.
abstract: OBJECTIVE
  Nerve root decompression to relieve pain and radiculopathy remains one of the main goals of fusion-promoting procedures in the subaxial cervical spine. The use of allograft facet spacers has been suggested as a potential alternative for performing foraminotomies to increase the space available for the cervical nerve roots while providing segmental stiffening. Therefore, the goal of this cadaveric biomechanical study was to determine the acute changes in kinetics and foraminal area after the insertion of cortical bone facet spacers into the subaxial cervical spine.
  
  
  METHODS
  Allograft spacers (2 mm in height) were placed bilaterally into cadaveric cervical spine specimens (C2-T1, age of donors 57.5 ± 9.5 years, n = 7) at 1 (C4-5) and 3 (C3-6) levels with and without laminectomies and posterior lateral mass screw fixation. Standard stereophotogrammetry under pure moment loading was used to assess spinal kinetics. In addition, the authors performed 3D principal component analysis of CT scans to determine changes in foraminal cross-sectional area (FCSA) available for the spinal nerve roots.
  
  
  RESULTS
  Generally, the introduction of 2-mm-height facet spacers to the cervical spine produced mild, statistically insignificant reductions in motion with particular exceptions at the levels of implantation. No significant adjacent-level motion effects in any bending plane were observed. The addition of the posterior instrumentation (PI) to the intact spines resulted in statistically significant reductions in motion at all cervical levels and bending planes. The same kinetic results were obtained when PI was added to spines that also had facet spacers at 3 levels and spines that had been destabilized by en bloc laminectomy. The addition of 2-mm facet spacers at C3-4, C4-5, and C5-6 did produce statistically significant increases in FCSA at those levels.
  
  
  CONCLUSIONS
  The addition of allograft cervical facet spacers should be considered a potential option to accomplish indirect foraminal decompression as measured in this cadaveric biomechanical study. However, 2-mm spacers without supplemental instrumentation do not provide significantly increased spinal segmental stability.
authors.affiliation: Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, Maryland;
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Maulucci
authors.affiliation: Department of Neurosurgery, University of Maryland School of Medicine, Baltimore, Maryland;
authors.forename: Charles A
authors.initials: CA
authors.lastname: Sansur
authors.affiliation: Medtronic Spinal and Biologics, Memphis, Tennessee; and.
authors.forename: Vaneet
authors.initials: V
authors.lastname: Singh
authors.affiliation: Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Cholewczynski
authors.affiliation: Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado.
authors.forename: Snehal S
authors.initials: SS
authors.lastname: Shetye
authors.affiliation: Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado.
authors.forename: Kirk
authors.initials: K
authors.lastname: McGilvray
authors.affiliation: Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado.
authors.forename: Christian M
authors.initials: CM
authors.lastname: Puttlitz
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000009:adverse effects; D002574:Cervical Vertebrae / Q000601:surgery*; D019299:Decompression, Surgical / Q000379:methods; D005260:Female; D006801:Humans; D007596:Joints / Q000601:surgery; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D013123:Spinal Fusion / Q000379:methods; D014184:Transplantation, Homologous
keywords: 1FS = 1-level facet spacer; 3FS = 3-level facet spacer; FCSA = foraminal cross-sectional area; LAM = en bloc laminectomy; PI = posterior instrumentation; ROM = range of motion; biomechanics; cervical spine; facet spacers; foraminal area