Background and Objectives:
Knowledge of spine segment motion patterns or “kinematics” is of interest to understanding the time-dependent or viscoelastic behavior of the spine, postural kinematics, vibration response of the spine, and response of the spine to chiropractic manipulations. The ability to quantify in vivo spine segment “kinematics” is clinically significant in terms of both the diagnosis and treatment of spinal disorders and LBP. The objectives of this study were to a) study the relative motions of the normal and abnormal lumbar spine in response to transverse (postero-anterior) manipulative thrusts, and b) mathematically model the dynamic viscoelastic behavior of the spine.
An intervertebral motion measuring device (IMD) was used to quantify the in vivo Interspinous kinematic behavior of the normal (1 volunteer) and unstable (2 patients with abnormal lumbar discs consulting for spine surgery) human lumbar spine. The IMD is a spatial linkage system capable of measurement of motion in the sagittal plane, and was rigidly attached to the L2-L3 and L3-L4 spinous processes using 2.4 mm Steinmann pins. Rotation, translation and shear of the lumbar vertebrae were obtained in response to transverse impulses from an Activator adjusting instrument (AAI) applied to the spinous process of adjacent segments of the thoraco-lumbar spine with the patients lying prone. Impulse force and acceleration in transverse plane were measured using a uniaxial load cell and accelerometer.
The impulses (= 100N peak, < 100 msec duration) produced exponentially damped oscillations in the lumbar motion segment with displacement amplitude peaks (axial=0.5-1.0 mm, shear = 0.1-0.3 mm, rotation=0.5-1 degrees) located at frequencies ranging from 10-15 Hz. Alterations in the propagation of the impulse stimulus were observed in the two patients with disc pathology. The kinematic data is currently being analyzed using a dynamic, three-parameter linear solid viscoelastic model to obtain intrinsic properties of the: ‘spine (moduli or stiffness and viscosity).
Although this study was conducted using only a few human subjects, the preliminary results suggest that one may be able to discriminate between normal and abnormal kinematic behavior by measuring and analyzing the impulse response. of the spine in viva. Such measurements may be used to evaluate the mechanical effectiveness of various manipulative, surgical and rehabilitative procedures of the spine.
Reference: T. Keller, PhD, M. Nathan, MS, and A. Kaigle, MS Dept. of Mechanical Engr. University of Vermont. Burlington, VT and Depts. of Orthopedics (Occupational Unit), Sahlgren Hospital, Goteborg, Sweden. Proceedings of the FCER’s 1993 International Conference on Spinal Manipulation. Montreal, Quebec, Canada, April 30-May 1: pp. 51-5.