In Vitro Biomechanical Comparison of Cervical Disk Arthroplasty, Ventral Slot Procedure, and Smooth Pins with Polymethylmethacrylate Fixation at Treated and Adjacent Canine Cervical Motion Units

Abstract

To compare the biomechanical properties of cervical arthroplasty to a ventral slot procedure and pin-polymethylmethacrylate (pin-PMMA) fixation. Fresh cadaveric cervical (C2-T1) spines from 6 large dogs. Four spinal conditions were studied in each spinal specimen: intact, disk arthroplasty, ventral slot, and fixation with smooth pin-PMMA at C5-C6 intervertebral space. Axial compression, torsion, flexion-extension, and lateral bending moments were sequentially tested on each specimen for the 4 spinal conditions. Data from the C3-C4, C4-C5, C5-C6, and C6-C7 vertebral motion units (VMUs) were compared among treatments. In axial compression and torsion, the ventral slot procedure allowed significantly less motion than intact, pin-PMMA, and arthroplasty groups at C5-C6. In lateral bending and flexion-extension, pin-PMMA had the least motion of C5-C6, followed by the arthroplasty group, intact spine, and ventral slot, all of which were significantly different from each other. Overall, the artificial disk was better able to mimic the behavior of the intact specimens compared with the ventral slot and pin-PMMA, producing similar displacements in axial compression and rotation in torsion, but more limited motion than intact in flexion-extension and in lateral bending. Cervical spine specimens with an implanted prosthesis have biomechanical behaviors more similar to an intact spine compared with spinal specimens with ventral slot and pin-PMMA procedures. Cervical arthroplasty may then preserve some of the motion in the affected area after neural decompression while providing distraction. Cervical arthroplasty should be further investigated in vivo to determine if it is a viable alternative to the ventral slot or pin-PMMA procedures for surgical treatment of cervical diseases in dogs and in particular for treatment of disk-associated caudal cervical spondylomyelopathy.