EFFECT OF PIN HOLE SIZE AND NUMBER ON IN-VITRO BONE STRENGTH IN THE EQUINE RADIUS LOADED IN TORSION

Objective-To determine the effect of pin hole size and number on the b reaking strength of the adult equine radius when loaded in torsion to failure. Sample Population-54 pairs of equine radii from adult horses. Procedure-For test one, 12 pairs of radii were used to determine the effect of pin hole size on torsional breaking strength. A 6.35-mm hole was drilled in 1 radius, and a 9.5-mm hole was drilled in the contral ateral radius. For test two, 36 pairs of radii were randomly assigned to 1 of 3 treatment groups (n = 12) to determine the effect of pin hol e number on the torsional breaking strength of the equine radius. One radius of each pair served as a control, and one, three, or six 6.35-m m transcortical holes were drilled in the contralateral radius. For te st three, 6 pairs of radii had torsional forces applied directly to th e transfixation pins, as opposed to the bone itself. One radius of a p air served as a control, and three 6.35-mm smooth Steinman pins were p laced in the contralateral radius. All radii were loaded in torsion to failure, and the breaking strengths were recorded. Results-Compared w ith the 6.35-mm hole, the 9.5-mm hole significantly decreased torsiona l strength of the radius. There was no significant difference in mean torsional strength between the control radii and the radii with 1, 3, or 6 transcortical holes or when the transfixation pins were loaded. C onclusion-Use of up to three 6.35-mm transfixation pins can be used in a full-limb transfixation pin cast to optimize stiffness without a si gnificant decrease (12%) in bone strength.