Kinematics of the canine lumbar intervertebral joint. An in vivo study before and after adjacent instrumentation

Abstract

Study design: In vivo, canine lumbar spine intervertebral motion was measured before and after instrumentation of caudal segments. The three-dimensional kinematics of the intervertebral joint were described using helical axes and Fourier series.

Objective: The in vivo three-dimensional kinematics of the intervertebral joint were measured and described. An animal model where intervertebral motion could be repeatedly changed was developed.

Summary of background data: The kinematics of intervertebral joints have been described from results of extensive in vitro testing, some limited in vivo testing, and clinically by evaluation of flexion/extension films. In the canine, in vivo intervertebral motion has been described previously, but the method possessed some measurement artifact.

Methods: In vivo, four canines had motion data collected (L2-L3) while the animals walked on a treadmill. L3 To L7 were instrumented in all of the animals and motion testing was repeated 1 and 12 weeks later. Helical axes of motion were determined for each gait cycle. Fourier series were fit to the motion data, helical axis parameters, and Fourier coefficients were all statistically compared (pre- and postinstrumentation).

Results: Vertebral rotations (coronal plane) and excursion of the L2/3 facet increased significantly (P < 0.01) after caudal instrumentation. Helical axes were oriented in a ventral direction and only the angle of rotation about the axis changed significantly (P < 0.05) after instrumentation of caudal segments. The Fourier coefficients (amplitudes) showed a significant (P < 0.05) increase in the coronal plane rotations only, after adjacent instrumentation.

Conclusion: The in vivo kinematics of the intervertebral joint have been completely defined in this study. Some motion characteristics compare very well to human motion. Since motion at an intervertebral joint now can be repeatedly altered, this animal model shows promise as a useful tool for investigation of tissue response to changes in motion at a joint.