Biomechanical comparison of 2 veterinary locking plates to monocortical screw/polymethylmethacrylate fixation in canine cadaveric cervical vertebral column

OBJECTIVE: To compare the biomechanical properties of 2 veterinary locking plates and monocortical screws/polymethylmethacrylate (PMMA) fixation in canine cadaveric cervical vertebral columns.

STUDY DESIGN: Biomechanical cadaveric study.

MATERIALS: Nineteen cervical vertebral columns (C2-C7) from large breed, skeletally mature, canine cadavers were used. A cortical ring was placed as a disk spacer at C4-C5 in all specimens. Seven vertebral columns were plated at C4-C5 with two 4-hole, 3.5 mm string of pearls plates (SOP) and 6 vertebral columns were plated with two 6-hole, 2.4 mm titanium locking reconstruction plates (Ti recon plate). All screws were placed monocortically. Six vertebral columns had monocortical titanium screws and PMMA (Ti screws/PMMA) placed, tested as part of a prior study.

METHODS: Stiffness testing in 3 directions was performed of the unaltered C4-C5 vertebral motion unit and repeated after placement of the disk spacer and implants. Data were compared using a linear mixed model that incorporated data from previously tested spines (Ti screw/PMMA).

RESULTS: The mean (95% CI) stiffness (N/m) in extension for SOP was 407 N/mm (330-503), for Ti recon plate was 284 N/mm (198-407) and for Ti screws/PMMA was 365 N/mm (314-428); in flexion for SOP was 250 N/mm (178-354), for Ti recon plate was 147 N/mm (106-204) and for Ti screws/PMMA was 311 (235-416); in lateral bending for SOP was 528 N/mm (441-633), for Ti recon plate was 633 N/mm (545-735) and for Ti screws/PMMA was 327 N/mm (257-412). There were no significant differences in stiffness between the 3 fixations for any outcome.

CONCLUSION: Monocortical fixation with two 3.5 mm SOP or two 2.4 mm Ti recon plates may be an alternate fixation to monocortical screws and PMMA.