Abstract
Objective The aim of this study was to evaluate the effect of bidirectional insertion on axial
pullout strength of tapered run out (TRO), traditional negative profile (TNP) and
positive profile (PP) pins.
Study Design Cadaveric adult canine tibiae were harvested. Tapered run out pins (Group 1) were
inserted unidirectionally to the desired position; bidirectionally past the desired
position, then withdrawn to the desired position (Group 2); and bidirectionally as
described for Group 2, repeated twice (Group 3). Traditional negative profile pins
(Group 4–6) and PP pins (Group 9–11) were placed in the same manner. Tapered run out
(Group 7), TNP (Group 8) and PP pins (Group 12) were driven unidirectionally such
that the shaft of the pin violated the cis-cortex. A servohydraulic testing machine
extracted the pins and measured axial peak pullout strength.
Results Positive profile pins had significantly greater pullout strength than TRO and TNP
pins placed unidirectionally to the desired position. Method of insertion had no effect
on peak pullout strength of TNP pins. TRO and PP pins inserted unidirectionally to
the desired position had significantly greater peak pullout strengths than insertion
bidirectionally or if the shaft of the pin violated the cis-cortex.
Conclusion The authors recommend that pins used for external skeletal fixation should be placed
unidirectionally to the desired position with fluoroscopic guidance, intra-operative
depth gauge measurements or measurements from preoperative radiographs. Repositioning
pins results in loss of peak pullout strength with TRO and PP pins.
Keywords
tapered run out - pin loosening - bidirectional insertion - external skeletal fixation
- dogs
