Effect of Facetectomy on the Three-Dimensional Biomechanical Properties of the Fourth Canine Cervical Functional Spinal Unit: A Cadaveric Study.

Objective To study the biomechanical effect of facetectomy in 10 large breed dogs (>24 kg body weight) on the fourth canine cervical functional spinal unit. Methods Canine cervical spines were freed from all muscles. Spines were mounted on a six-degrees-of-freedom spine testing machine for three-dimensional motion analysis. Data were recorded with an optoelectronic motion analysis system. The range of motion was determined in all three primary motions as well as range of motion of coupled motions on the intact specimen, after unilateral and after bilateral facetectomy. Repeated-measures analysis of variance models were used to assess the changes of the biomechanical properties in the three treatment groups considered. Results Facetectomy increased range of motion of primary motions in all directions. Axial rotation was significantly influenced by facetectomy. Coupled motion was not influenced by facetectomy except for lateral bending with coupled motion axial rotation. The coupling factor (coupled motion/primary motion) decreased after facetectomy. Symmetry of motion was influenced by facetectomy in flexion-extension and axial rotation, but not in lateral bending. Clinical Significance Facet joints play a significant role in the stability of the cervical spine and act to maintain spatial integrity. Therefore, cervical spinal treatments requiring a facetectomy should be carefully planned and if an excessive increase in range of motion is expected, complications should be anticipated and reduced via spinal stabilization.