Objective—To conduct an in vitro investigation of the
biomechanical characteristics of the canine lumbar
spinal column in flexion and extension and measure
the destabilizing effects of multiple consecutive unilateral
and bilateral hemilaminectomies.
Sample Population—30 isolated multisegmental
spinal units (L1-L4) from nonhypochondroplastic dogs
weighing 15 to 30 kg.
Procedure—Physically normal and surgically altered
spinal specimens were subjected to 4-point bending
in flexion and extension to determine effects of multiple
consecutive hemilaminectomies on the basis of
analysis of test system load-displacement data. Six
groups with 5 spinal columns in each were defined on
the basis of the following procedures: hemilaminectomy
at L2-L3, 2 adjacent hemilaminectomies at L1-
L3, 3 adjacent hemilaminectomies at L1-L4, bilateral
hemilaminectomies at L2-L3, 2 bilateral hemilaminectomies
at L1-L3, and no hemilaminectomy (intact).
Spinal stability before and after surgery was determined
in all groups. Each group served as its own
control for nondestructive testing. Spinal strength
was evaluated through destructive testing to determine
deformation at failure, strength to failure, and
mode of catastrophic failure. The intact group served
as the control for destructive testing.
Results—Stability in extreme flexion and extreme
extension did not change significantly following any
hemilaminectomy procedure. Postoperative stability
within the neutral zone was significantly decreased in
all groups. Range of motion within the neutral zone
was not significantly different from the intact condition
in any group.
Conclusions and Clinical Relevance—Multiple
hemilaminectomies did not decrease stiffness of the
lumbar spinal column during flexion and extension.
These results support clinical recommendations
regarding multiple consecutive hemilaminectomies in
dogs. (Am J Vet Res 2003;64:1139–1145)