Validation of the cat as a model for the human lumbar spine during simulated high-velocity, low-amplitude spinal manipulation.

Abstract

High-velocity, low-amplitude spinal manipulation (HVLA-SM) is an efficacious treatment for low back pain, although the physiological mechanisms underlying its effects remain elusive. The lumbar facet joint capsule (FJC) is innervated with mechanically sensitive neurons and it has been theorized that the neurophysiological benefits of HVLA-SM are partially induced by stimulation of FJC neurons. Biomechanical aspects of this theory have been investigated in humans while neurophysiological aspects have been investigated using cat models. The purpose of this study was to determine the relationship between human and cat lumbar spines during HVLA-SM. Cat lumbar spine specimens were mechanically tested, using a displacement-controlled apparatus, during simulated HVLA-SM applied at L5, L6, and L7 that produced preload forces of approximately 25% bodyweight for 0.5 s and peak forces that rose to 50-100% bodyweight within approximately 125 ms, similar to that delivered clinically. Joint kinematics and FJC strain were measured optically. Human FJC strain and kinematics data were taken from a prior study. Regression models were established for FJC strain magnitudes as functions of factors species, manipulation site, and interactions thereof. During simulated HVLA-SM, joint kinematics in cat spines were greater in magnitude compared with humans. Similar to human spines, site-specific HVLA-SM produced regional cat FJC strains at distant motion segments. Joint motions and FJC strain magnitudes for cat spines were larger than those for human spine specimens. Regression relationships demonstrated that species, HVLA-SM site, and interactions thereof were significantly and moderately well correlated for HVLA-SM that generated tensile strain in the FJC. The relationships established in the current study can be used in future neurophysiological studies conducted in cats to extrapolate how human FJC afferents might respond to HVLA-SM. The data from the current study warrant further investigation into the clinical relevance of site targeted HVLA-SM.