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.

Fig. 1

Experimental setup for simulated spinal manipulation using a cat lumbar spine specimen. Specimens were fixed in the neutral posture using the spine fixation apparatus. A linear actuator was coupled to the L5, L6, or L7 vertebral body and actuated in the direction shown. The load cell measured the developed force. CCD cameras optically tracked markers attached to L5–L7 transverse processes for kinematic measurements and CMOS cameras were used for optically measuring facet joint capsule strain.

Fig. 2

Representative data from simulated spinal manipulation applied to L6. Displacement was the controlled parameter. Developed force, IVA, RVT, and facet joint capsule principal strain magnitudes (L6–7 shown) were measured simultaneously. Note that displacements were applied in the x-direction and the negative force values indicate loading in the same direction.

Fig. 3

Developed load during simulated manipulation for cat lumbar spine specimens during the preload and peak impulse. Peak force with constant total vertebral displacement was significantly greater when the manipulation was applied to L7 compared with L5 and L6 (one-way analysis of variance with post-hoc Student–Newman–Keuls test; p <0.05). Error bars show standard deviations.

Fig. 4

RVT during simulated spinal manipulation in cat and human lumbar spine specimens. Error bars show standard deviations.

Fig. 5

IVA during simulated spinal manipulation using cat and human lumbar spine specimens. Error bars show standard deviations.

Fig. 6

Cat lumbar facet joint capsule strain magnitudes during simulated manipulation applied at L5, L6, or L7. Manipulations were delivered at the manipulation site indicted by applying a simultaneous translation (right to left) and rotation (counterclockwise) of the vertebrae. Error bars show standard deviations.

Fig. 7

Human lumbar facet joint capsule strain magnitudes during simulated spinal manipulation applied to the anterior aspect of L3, L4, or L5. Manipulations were delivered by applying a simultaneous translation (right to left) and rotation (counterclockwise) of the manipulated vertebra. Error bars show standard deviations.