The mechanical properties of the canine lumbar disc and motion segment.

A study was initiated to measure the mechanical properties of the canine lumbar spine disc and motion segment at two specific levels. Compressive stiffness was determined to be 717.8 N/mm at L2-3 and 949.0 N/mm at L5-6. Torsional stiffness was found to be 1.04 Nm/deg at L2-3 and 1.72 Nm/deg at L5-6. These data were then compared to human lumbar spine disc and motion segment properties that have been reported in the literature. After normalizing for size differences, the canine lumbar disc showed a similar axial modulus (14.03 MPa for L2-3 and 16.30 MPa for L5-6) and a significantly higher torsional modulus (30.80 MPa for L2-3 and 26.17 MPa for L5-6) when compared to human values. The relative contributions of ligaments, posterior elements, and intervertebral disc to overall stability of the motion segment was found to be similar in canines and humans. As has been shown in human spine research, the posterior elements including the facet joints were found to be significant structures in providing torsional rigidity of the canine spine.