Summary
This in vitro study compares the biomechanical properties of two methods of ilial
fracture repair in dogs. Ten pelves were harvested from skeletally mature mixed breed
dogs weighing 20–27 kg and bilateral oblique ilial body osteotomies were created.
One hemipelvis from each dog was stabilized with a 2.7 mm plate and screws and the
contralateral hemipelvis was stabilized with a five pin linear external fixator construct.
Each hemipelvis was mounted at an angle of 30° to an actuator platform, such that
the acetabulum was centrally loaded by a steel sphere attached to the load cell of
a servohydraulic materials testing machine. The construct was loaded at a constant
rate of 20 mm/min. A load/displacement curve was generated for each hemipelvis by
plotting the sustained load against the actuator movement. The stiffness, yield load
and failure load for each hemipelvis were determined from the load/displacement curve.
Bending stiffness was defined as the slope of the load/displacement curve from 100
N to yield load. The mode of failure was determined by observations made during testing
and gross inspection of each specimen. The mean construct stiffness, yield load and
failure load were compared between stabilization groups using a Student’s paired t-test
with statistical significance set at p>0.05. Nine out of 10 of the hemipelves that
were stabilized by plates and screws failed catastrophically by fracture through the
caudal screw holes and nine out of 10 of the hemipelves that were stabilized using
an external fixator failed by fracture of the ischium in the region supported by the
mounting roller, propagating through the most caudal ischial pin. There was not any
significant difference (P = 0.22) in bending stiffness between stabilization techniques,
but yield (1467 N vs 2620 N; P = 0.04) and failure (1918 N vs 2687 N; P = 0.002) loads
were significantly greater for hemipelves stabilized with external fixators.
Keywords
Ilial osteotomy - plating - external fixation - biomechanics
