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

Abstract

OBJECTIVE : To assess biomechanical properties of 2 veterinary locking plates and compare fixation among these plates and monocortical screws/polymethylmethacrylate (PMMA) fixation in cadaveric canine cervical vertebral columns. STUDY DESIGN : Biomechanical cadaveric study. MATERIALS : Nineteen large breed cadaveric canine cervical vertebral columns (C2-C7) from skeletally mature dogs were used. A cortical ring was placed as disk spacer at C4-C5 in all specimens. Seven vertebral columns were implanted at C4-C5 with two 4-hole,3.5mm string of pearls plates (SOP) and 6 were implanted with two 6-hole, 2.4mm titanium locking reconstruction plates (Ti recon plate). All screws were placed monocortically. Six specimens were implanted with monocortical titanium screws and PMMA (Ti screws/PMMA), 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 implant fixation. Data were compared using a linear mixed model that incorporated data from previously tested spines (Ti screw/PMMA). RESULTS :: The mean post-fixation stiffness (N/m) and 95% confidence intervals for SOP, Ti recon plate and Ti screws/PMMA respectively were 407 (330,503), 284 (198,407) and 365 (314,428) in extension; 250 (178,354), 147 (106,204) and 311 (235,416) in flexion; and 528 (441,633), 633 (545,735) and 327 (257,412) in lateral bending. There were no significant differences in stiffness increase among the 3 fixation methods within any evaluated measurement directions. CONCLUSIONS : Monocortical fixation with two 3.5mm SOP and two 2.4mm Ti recon plates may offer an alternative fixation to monocortical screws and PMMA.