| ABSTRACT: |
An animal model of lumbar spinal stenosis was
developed in which the pathophysiology of this condition could be examined.
Four experimental groups, each containing six dogs, were studied. One group
had a laminectomy of the sixth and seventh lumbar vertebrae only; these
animals served as controls. In the three other groups, a laminectomy was
performed and the cauda equina was constricted by 25, 50, or 75 per cent
to produce chronic compression. Cortical evoked potentials were recorded
preoperatively, immediately after constriction, and at one, two, and three
months postoperatively. Daily neurological examinations were carried out,
and the neurological deficits were graded using the Tarlov system. After
three months of constriction, the cauda equina of three dogs in each group
was examined histologically, and the vascular circulation was examined by
latex and India-ink injection with a modification of the Spalteholz technique.
The animals in the control group showed no neurological abnormalities, no
changes in cortical evoked potentials, normal microvascularity, and no histopathological
changes in the nerve roots or the spinal cord. The dogs in which the cauda
equina had been constricted 25 per cent had no neurological deficits, mild
changes in cortical evoked potentials, slight histological changes, and
venous congestion of the root and dorsal root ganglion of the seventh lumbar
nerve. The dogs in which the cauda equina had been constricted 50 per cent
had mild initial motor weakness, major changes in cortical evoked potentials,
edema and loss of myelin in the root of the seventh lumbar nerve, and moderate
or severe venous congestion of the root and dorsal root ganglion of the
seventh lumbar nerve. The dogs in which the cauda equina had been constricted
75 per cent had significant weakness, paralysis of the tail, and urinary
incontinence; two dogs recovered by the third month, but all had neurogenic
claudication for three months. All six dogs had dramatic changes in cortical
evoked potentials and had complete nerve-root atrophy at the level of the
constriction. There was blockage of axoplasmic flow and wallerian degeneration
of the motor nerve roots distal to the constriction and of the sensory roots
proximal to the constriction, as well as degeneration of the posterior column.
Severe arterial narrowing at the level of the constriction and venous congestion
of the roots and dorsal root ganglia of the seventh lumbar and first sacral
nerves were also present. Cortical evoked potentials revealed neurological
abnormalities before the appearance of neurological signs and symptoms.(ABSTRACT
TRUNCATED AT 400 WORDS) |