Study design: A prospective in vivo experimental animal study.
Objective: To determine the effects of disc degeneration and variable pulse duration mechanical excitation on dorsoventral lumbar kinematic responses.
Summary of background data: In vitro and in vivo biomechanical studies have examined spine kinematics during posteroanterior loading mimicking spinal manipulation therapy (SMT), but few (if any) studies have quantified SMT loading-induced spinal motion responses in the degenerated intervertebral disc.
Methods: Fifteen sheep underwent a survival surgical procedure resulting in chronic disc degeneration of the L1-L2 disc. Ten age- and weight-matched animals served as controls. Uniform pulse dorsoventral mechanical forces (80 N) were applied to the L3 spinous processes using 10-, 100-, and 200-ms duration pulses mimicking SMT. L3 displacement and L2-L1 acceleration in the control group were compared with the degenerated disc group.
Results: Dorsoventral displacements increased significantly (fivefold, P < 0.001) with increasing mechanical excitation pulse duration (control and degenerated disc groups). Displacements and L2-L1 acceleration transfer were significantly reduced (approximately 19% and approximately 50%, respectively) in the degenerated disc group compared with control (100- and 200-ms pulse duration protocols, P < 0.01).
Conclusion: Dorsoventral vertebral motions are dependent on mechanical excitation pulse duration and are significantly reduced in animals with degenerated discs.