In vitro comparison of metaphyseal and diaphyseal placement of centrally threaded, positive-profile transfixation pins in the equine third metacarpal bone.
OBJECTIVE
To evaluate in vitro holding power and associated microstructural and thermal damage from placement of positive-profile transfixation pins in the diaphysis and metaphysis of the equine third metacarpal bone.


METHODS
Third metacarpal bones from 30 pairs of adult equine cadavers.


METHODS
Centrally threaded positive-profile transfixation pins were placed in the diaphysis of 1 metacarpal bone and the metaphysis of the opposite metacarpal bone of 15 pairs of bones. Tensile force at failure for axial extraction was measured with a materials testing system. An additional 15 pairs of metacarpal bones were tested similarly following cyclic loading. Microstructural damage was evaluated via scanning electron microscopy in another 6 pairs of metacarpal bones, 2 pairs in each of the following 3 groups: metacarpal bones with tapped holes and without transfixation pin placement, metacarpal bones following transfixation pin placement, and metacarpal bones following transfixation pin placement and cyclic loading. Temperature of the hardware was measured with a surface thermocouple in 12 additional metacarpal bones warmed to 38 C.


RESULTS
The diaphysis provided significantly greater resistance to axial extraction than the metaphysis. There were no significant temperature differences between diaphyseal and metaphyseal placement. Microstructural damage was limited to occasional microfractures seen only in cortical bone of diaphyseal and metaphyseal locations. Microfractures originated during drilling and tapping but did not worsen following transfixation pin placement or cyclic loading.


CONCLUSIONS
Centrally threaded, positive-profile transfixation pins have greater resistance to axial extraction in the diaphysis than in the metaphysis of equine third metacarpal bone in vitro. This information may be used to create more stable external skeletal fixation in horses with fractures.
McClure
S R
SR
Department of Veterinary Clinical Sciences, Purdue University, West Lafayette, IN 47906-1248, USA.
Hillberry
B M
BM
Fisher
K E
KE
D000818:Animals; D018483:Diaphyses; D016267:External Fixators / Q000662:veterinary*; D050723:Fractures, Bone / Q000473:pathology / Q000628:therapy / Q000662:veterinary*; D006734:Horse Diseases / Q000473:pathology / Q000628:therapy*; D006736:Horses; D066298:In Vitro Techniques; D008663:Metacarpus / Q000648:ultrastructure; D008854:Microscopy, Electron / Q000662:veterinary; D013314:Stress, Mechanical