P01.01. Neural responses to the mechanical characteristics of a spinal manipulation: effect of varying segmental contact site
© Pickar et al; licensee BioMed Central Ltd. 2012
Published: 12 June 2012
A goal of our laboratory is to identify mechanisms of action operative during the body-based practice of spinal manipulation. Spinal manipulation can be identified by a number of mechanical characteristics, including but not limited to, contact site, magnitude, rate and direction of thrusting force. Because neural mechanisms are thought to contribute to its clinical effects, we studied spinal manipulation during a series of experiments aimed at identifying mechanical characteristics that affect responses from sensory neurons innervating paraspinal tissues. Presumably, specific parameters related to these characteristics are related to successful clinical outcomes. In this study, we determined the effect of contact site on manipulation-induced neural activity of proprioceptive afferents from lumbar paraspinal muscles.
In an anesthetized cat preparation, a simulated spinal manipulation [posterior-to-anterior; thrust amplitude = 21.3N (55% of an average cat’s body weight of 3.95 kg); thrust duration = 100ms] was delivered to the intact lower lumbar spine (L6 – S1) at each of 4 contact sites: L6 spinous process, left L6 mammillary process, left L6 lamina, and L7 spinous process. Electrophysiological recordings from individual muscle spindle afferents (n=16) innervating the L6 multifidus and longissimus muscles were obtained from L6 dorsal rootlets exposed through an L5 laminectomy. Changes in neural activity during the manipulative thrust were compared between the four contact sites.
All contact sites increased mean spindle activity: L6 spinous: 85 impulses per second (imp/s) (60, 100; lower, upper 95% CI); L6 lamina: 104 imp/s (79, 130); L6 mammillary 80 imp/s (55, 105); and L7 spinous 43 imp/s (18, 68). Lamina contact produced the largest increase, but only differences between the L7 spinous and each L6 contact site were statistically significant.
The data suggest that maximizing sensory input from segmental paraspinal tissues during a spinal manipulation requires specifically contacting that segmental level. In addition, a lamina contact may most effectively create the dynamic mechanical stimulus that evokes the sensory input.
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