title: Biomechanical analysis of disc pressure and facet contact force after simulated two-level cervical surgeries (fusion and arthroplasty) and hybrid surgery.
abstract: OBJECTIVE
  The objective of this study was designed to compare 2-level cervical disc surgery (2-level anterior cervical discectomy and fusion [ACDF] or disc arthroplasty) and hybrid surgery (ACDF/arthroplasty) in terms of postoperative adjacent-level intradiscal pressure (IDP) and facet contact force (FCF).
  
  
  METHODS
  Twenty-four cadaveric cervical spines (C3-T2) were tested in various modes, including extension, flexion, and bilateral axial rotation, to compare adjacent-level IDP and FCF after specified treatments as follows: 1) C5-C6 arthroplasty using ProDisc-C (Synthes Spine, West Chester, Pennsylvania, USA) and C6-C7 ACDF, 2) C5-C6 ACDF and C6-C7 arthroplasty using ProDisc-C, 3) 2-level C5-C6/C6-C7 disc arthroplasties, and 4) 2-level C5-C6/C6-C7 ACDF. IDPs were recorded at anterior, central, and posterior disc portions.
  
  
  RESULTS
  After 2-level cervical arthrodesis (ACDF), IDP increased significantly at the anterior annulus of distal adjacent-level disc during flexion and axial rotation and at the center of proximal adjacent-level disc during flexion. In contrast, after cervical specified treatments, including disc arthroplasty (2-level disc arthroplasties and hybrid surgery), IDP decreased significantly at the anterior annulus of distal adjacent-level disc during flexion and extension and was unchanged at the center of proximal adjacent-level disc during flexion. Two-level cervical arthrodesis also tended to adversely impact facet loads, increasing distal rather than proximal adjacent-level FCF.
  
  
  CONCLUSIONS
  Both hybrid surgery and 2-level arthroplasties seem to offer significant advantages over 2-level arthrodesis by reducing IDP at adjacent levels and approximating FCF of an intact spine. These findings suggest that cervical arthroplasties and hybrid surgery are an alternative to reduce IDP and facet loads at adjacent levels.
authors.affiliation: Department of Neurosurgery, Stanford University Medical Center, Stanford, California, USA.
authors.forename: Jon
authors.initials: J
authors.lastname: Park
authors.affiliation: Department of Neurosurgery, Stanford University Medical Center, Stanford, California, USA; Department of Neurosurgery, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea. Electronic address: zunzae@hanmail.net.
authors.forename: Jun Jae
authors.initials: JJ
authors.lastname: Shin
authors.affiliation: Department of Neurosurgery, Stanford University Medical Center, Stanford, California, USA.
authors.forename: Jesse
authors.initials: J
authors.lastname: Lim
mesh_terms: D001178:Arthroplasty; D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000502:physiology / Q000601:surgery*; D017586:Diskectomy; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology / Q000601:surgery*; D011312:Pressure; D019919:Prosthesis Implantation; D013123:Spinal Fusion; D021801:Zygapophyseal Joint / Q000502:physiology / Q000601:surgery*
keywords: Adjacent-segment degeneration; Cervical arthroplasty; Facet contact force; Hybrid surgery; Intradiscal pressure