The Journal of Bone and Joint Surgery, Vol 74, Issue 10 1464-1471, Copyright © 1992 by Journal of Bone and Joint Surgery, Inc
The effects of controlled mechanical loading on group-II, III, and IV afferent units from the lumbar facet joint and surrounding tissue. An in vitro study
AI Avramov, JM Cavanaugh, CA Ozaktay, TV Getchell and AI King
Bioengineering Center, Wayne State University, Detroit, Michigan 48202.
An in vitro model was developed to investigate the responses of afferent
units in the lumbar spine to controlled loading as measured by a load-cell.
The neuronal discharge was recorded simultaneously with loading. Three
types of neuronal responses were observed. The first type of response
involved phasic-type mechanoreceptors, which responded to movement,
regardless of direction or initial position. The response did not outlast
the movement phase of loading. These units may serve as velocity detectors.
The second type of response was seen in slowly adapting low-threshold
mechanoreceptors, which tended to respond to loading in the 0.3 to
0.5-kilogram range with an immediate and sustained increase in the rate of
firing. This type of response appears to be associated with the activation
of low-threshold group-II and group-III fibers, which were located in
muscles and tendons inserting into the facet joint. The third type of
response involved slowly adapting high-threshold mechanoreceptors, which
could not be activated until a threshold of three to five kilograms had
been exceeded. It appears that this type of response is at least partially
due to the activation of high-threshold group-III and group-IV capsular
afferent units, which may signal noxious mechanical stimulation.