Biomechanical Analysis of the Three-Dimensional Motion Pattern of the Canine Cervical Spine Segment C4-C5

Objective— To study the kinematics of cervical spine segment C4–C5 and its association with disc dimensions and the coupled motion (CM) in relation to primary motion (PM). Study Design— Cadaveric biomechanical study. Animals— Cadavers of large breed dogs (>20 kg; n=11). Methods— Spines were freed from muscles. Radiographs were taken orthogonal to the C4–C5 disc space and disc thickness, endplate width, and height were measured. Spines were mounted on a simulator for 3-dimensional motion analysis. Data were recorded with an optoelectronic motion analysis system. Range of motion (ROM) and neutral zone (NZ) were determined in the direction of flexion/extension, left/right lateral bending, and left/right axial rotation, as well as the ROM of CM. Results— ROM in flexion and extension was similar; there was no CM in flexion/extension. Left/right axial rotation and left/right lateral bending were coupled to the same side. CM was 1.72 and 3.56 times the ROM of the PM in lateral bending and axial rotation, respectively. Disc dimensions were positively correlated with body weight. Flexion/extension magnitude was significantly reduced for larger endplates, but axial rotation was not influenced. Lateral bending had no correlation with weight or disc dimensions. Conclusion— Left/right lateral bending and left/right axial rotation are coupled differently in the C4–C5 segment in dogs compared with humans. Clinical Relevance— The canine C4–C5 spinal segment has unique motion coupling patterns that should be considered for dynamic implant designs.