title: A cadaveric analysis of cervical fixation: the effect of intermediate fixation points and dynamization in multilevel cervical fusions.
abstract: OBJECTIVE
  The authors conducted a study to compare biomechanical effects on the cervical spine of bridging fixation and intermediate fixation techniques, in both fixed and dynamic modes.
  
  
  METHODS
  A biaxial, servohydraulic machine biomechanically tested 23 human cervical spines for stiffness and strain in compression, extension, flexion, and lateral bending through 3 specimen states: 1) intact, 2) defect (corpectomy and discectomy), and 3) grafting with plate application in 1 of 4 constructs: C3-7 dynamized long strut (DLS), C3-7 fixed long strut (FLS), C3-5-7 dynamized multisegment (DMS), and C3-5-7 fixed multisegment (FMS).
  
  
  RESULTS
  Compared with FMS, FLS had significantly greater strain in extension (at C-3 and at the rostral and caudal parts of the graft) and in lateral bending (at C-3 and at the caudal part of the graft). Fixed (FLS and FMS) constructs had greater flexion stiffness than did dynamized (DLS and DMS) constructs and showed a trend toward greater lateral bending stiffness. Instrumentation revealed greater extension strain with the long fixed (FLS and DLS) constructs than with the multifixed (FMS and FMS) constructs at the rostral and caudal parts of the graft but no significant differences between the dynamized (DLS and DMS) and fixed (FLS and FMS) constructs.
  
  
  CONCLUSIONS
  Multisegmental fixation provided greater stabilizing forces than did bridging constructs for both dynamized and fixed plates. Use of multisegmental fixation can potentially decrease strain at the screw-plate interface and reduce the rate of hardware failure.
authors.affiliation: Center for Spine Health and.
authors.forename: Daniel
authors.initials: D
authors.lastname: Lubelski
authors.forename: William E
authors.initials: WE
authors.lastname: McCormick
authors.forename: Lisa
authors.initials: L
authors.lastname: Ferrara
authors.forename: Edward C
authors.initials: EC
authors.lastname: Benzel
authors.forename: Mark
authors.initials: M
authors.lastname: Kayanja
mesh_terms: D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D017586:Diskectomy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods*; D013314:Stress, Mechanical
keywords: BMD = bone mineral density; COR = center of rotation; DLS = dynamized long strut; DMS = dynamized multisegment; DOC = dynamic osteosyntheos cervical; FLS = fixed long strut; FMS = fixed multisegment; cadaveric biomechanical study; cervical fixation; dynamic plates; fixed plates; intermediate fixation; multisegmental fixation