LIGAMENTO-MUSCULAR PROTECTIVE REFLEX IN THE LUMBAR SPINE OF THE FELINE

A ligamento-muscular protective reflex in the lumbar spine was demonst rated in a feline model. Stimulating electrodes were applied to the su praspinous ligament between several lumbar vertebra (L1 to L6) while r ecording myoelectric discharge from the paraspinal muscles at the L3, L4 and L5, bilaterally. Electromyographic (EMG) activity was present i n the paraspinal muscles bilaterally, upon stimulation of the supraspi nous ligament, in six preparations. The EMG discharge was strongest in the muscles one level below that of the stimulated ligament, whereas weaker EMG signals were recorded from as far as two levels above and b elow. The mean time delay between the application of the stimulus to t he ligament to the resulting EMG ranged from 2.52 to 2.77 ms at all le vels. Stimulation of the supraspinous ligament in the L6 segment resul ted in a weak reflex response, and stimulation in the L7 segment did n ot produce any EMG activity. It was concluded that mechanoreceptors in the supraspinous ligament at the L1/6 levels may initiate sensory sig nals upon strain of the ligament, during flexion. This, in turn, cause s contraction of the paraspinal muscles, bilaterally, to extend the sp ine and prevent possible damage to the ligament while maintaining stab ility. The results may add to the understanding of low back pain, and to the formulation of surgical procedures which could spare the neural supply of the ligament, allowing advanced physiotherapeutic modalitie s to be implemented for post-surgical rehabilitation. (C) 1998 Elsevie r Science Ltd. All rights reserved.