The Journal of Bone and Joint Surgery, Vol 72, Issue 6 865-870, Copyright © 1990 by Journal of Bone and Joint Surgery, Inc
Mechanosensitive afferent units in the lumbar facet joint
T Yamashita, JM Cavanaugh, AA el-Bohy, TV Getchell and AI King
Bioengineering Center, Wayne State University, Detroit, Michigan 48202.
The purpose of this study was to characterize somatosensory units of the
lumbar facet joint, which may play a central role in idiopathic low-back
pain. A laminectomy was performed on the lumbar spine of adult male New
Zealand White rabbits. Receptive fields of mechanosensitive afferent units
were investigated in the lumbar facet joint and adjacent surrounding
tissues, and electrophysiological recordings were obtained from filaments
of the dorsal root. Twenty-four units were identified in the region of the
facet joint: ten, in the capsule of the joint; twelve, in the border
regions between capsule and muscle or tendon; and two, in the ligamentum
flavum. Of these units, two had a conduction velocity that was slower than
2.5 meters per second (group IV), fifteen had a velocity ranging from 2.5
to twenty meters per second (group III), and seven had a velocity faster
than twenty meters per second. Seven units had a von Frey threshold of more
than 6.0 grams, thirteen had a threshold of less than 6.0 grams, and four
were not examined. Seven units in the facet joint responded to movement of
the joint. Fourteen other mechanosensitive units were found in the muscle,
tendon, and interspinous ligament; seven had a conduction velocity of 2.5
to twenty meters per second, and seven had a velocity that was faster than
twenty meters per second.
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