||Relative degrees (25%, 50% or 75%) of constriction
of the entire cauda equina at the seventh lumbar level were performed on
eighteen pure bred female beagle hounds by surgically implanting a circular
polyethylene loop with an imbedded stainless steel wire. The wire was mechanically
constricted by external control and the degree of compression was confirmed
by pre- and postoperative magnetic resonance imaging or computed tomography
scanning. A control group of two dogs had laminectomy only. Neurologic function
was evaluated daily. Cystometrics were performed on each dog after constriction
had been present for three months. Cortical evoked potentials (CEPs) were
obtained on all dogs preoperatively, immediately following constriction
and at monthly intervals for three months. Dogs were sacrificed at three
months and the cauda equina and spinal cord were examined histopathologically.
Cystometric tracings were noted to become a flat line with 75% compression
of the cord. Less compression had minimal effect on the cystometric curves.
The mean latency, determined by cortical evoked potentials, was noted to
increase by 3.2%, 7.8%, and 17.2% immediately after 25%, 50% and 75% constriction,
respectively. Histologic changes ranged from occasional enlargement of the
axons on the periphery of the cauda equina with 25% constriction to severe
loss of all axons and atrophic roots at the level of the constricting band
with 75% constriction.