Effect of an Intervertebral Disk Spacer on Stiffness After Monocortical Screw/Polymethylmethacrylate Fixation in Simulated and Cadaveric Canine Cervical Vertebral Columns. Issue 8 (11th February 2014) - Hettlich, Bianca F.
Abstract Objective To determine the biomechanical effect of an intervertebral spacer on construct stiffness in a PVC model and cadaveric canine cervical vertebral columns stabilized with monocortical screws/polymethylmethacrylate (PMMA). Study Design Biomechanical study. Sample Population PVC pipe; cadaveric canine vertebral columns. Methods PVC model—PVC pipe was used to create a gap model mimicking vertebral endplate orientation and disk space width of large‐breed canine cervical vertebrae; 6 models had a 4‐mm gap with no spacer (PVC group 1); 6 had a PVC pipe ring spacer filling the gap (PCV group 2). Animals—large breed cadaveric canine cervical vertebral columns (C2–C7) from skeletally mature dogs without (cadaveric group 1, n = 6, historical data) and with an intervertebral disk spacer (cadaveric group 2, n = 6) were used. All PVC models and cadaver specimens were instrumented with monocortical titanium screws/PMMA. Stiffness of the 2 PVC groups was compared in extension, flexion, and lateral bending using non‐destructive 4‐point bend testing. Stiffness testing in all 3 directions was performed of the unaltered C4–C5 vertebral motion unit in cadaveric spines and repeated after placement of an intervertebral cortical allograft ring and instrumentation. Data were compared using a linear mixed model approach that also incorporated data from previously tested spines with the same screw/PMMA construct but without disk spacer (cadaveric group 1). Results Addition of a spacer increased construct stiffness in both the PVC model (P < .001) and cadaveric vertebral columns (P < .001) compared to fixation without a spacer. Conclusions Addition of an intervertebral spacer significantly increased construct stiffness of monocortical screw/PMMA fixation.