In vitro biomechanical evaluations of screw-bar-polymethylmethacrylate and pin-polymethylmethacrylate internal fixation implants used to stabilize the vertebral motion unit of the fourth and fifth cervical vertebrae in vertebral column specimens from dogs.
OBJECTIVE
To determine the change in stiffness as evaluated by the dorsal bending moment of cervical vertebral specimens obtained from canine cadavers after internally stabilizing the vertebral motion unit (VMU) of C4 and C5 with a traditional pin-polymethylmethacrylate (PMMA) fixation implant or a novel screw-bar-PMMA fixation implant.


METHODS
12 vertebral column specimens (C3 through C6) obtained from canine cadavers.


METHODS
A dorsal bending moment was applied to the vertebral specimens before and after fixation of the VMU of C4 and C5 by use of a traditional pin-PMMA implant or a novel screw-bar-PMMA implant. Biomechanical data were collected and compared within a specimen (unaltered vs treated) and between treatment groups. Additionally, implant placement was evaluated after biomechanical testing to screen for penetration of the transverse foramen or vertebral canal by the pins or screws.


RESULTS
Treated vertebral specimens were significantly stiffer than unaltered specimens. There was no significant difference in stiffness between vertebral specimen groups after treatment. None of the screws in the novel screw-bar-PMMA implant group penetrated the transverse foramen or vertebral canal, whereas there was mild to severe penetration for 22 of 24 (92%) pins in the traditional pin-PMMA implant group.


CONCLUSIONS
Both fixation treatments altered the biomechanical properties of the cervical vertebral specimens as evaluated by the dorsal bending moment. There was reduced incidence of penetration of the transverse foramen or vertebral canal with the novel screw-bar-PMMA implant, compared with the incidence for the traditional pin-PMMA implant.
Hicks
Daniel G
DG
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA 99164, USA.
Pitts
Marvin J
MJ
Bagley
Rodney S
RS
Vasavada
Anita
A
Chen
Annie V
AV
Wininger
Fred A
FA
Simon
Julianna C
JC
D000818:Animals; D001696:Biomechanical Phenomena; D001843:Bone Cements; D001858:Bone Nails; D001863:Bone Screws; D002574:Cervical Vertebrae; D004285:Dogs / Q000033:anatomy & histology*; D005593:Fracture Fixation, Internal / Q000379:methods / Q000662:veterinary*; D019904:Polymethyl Methacrylate; D016059:Range of Motion, Articular / Q000502:physiology
D001843:Bone Cements; D019904:Polymethyl Methacrylate