In vitro comparison of the use of two large-animal, centrally threaded, positive-profile transfixation pin designs in the equine third metacarpal bone.
OBJECTIVE
To compare the in vitro holding power and associated microstructural damage of 2 large-animal centrally threaded positive-profile transfixation pins in the diaphysis of the equine third metacarpal bone.


METHODS
25 pairs of adult equine cadaver metacarpal bones.


METHODS
Centrally threaded positive-profile transfixation pins of 2 different designs (ie, self-drilling, self-tapping [SDST] vs nonself-drilling, nonself-tapping [NDNT] transfixation pins) were inserted into the middiaphysis of adult equine metacarpal bones. Temperature of the hardware was measured during each step of insertion with a surface thermocouple. Bone and cortical width, transfixation pin placement, and cortical damage were assessed radiographically. Resistance to axial extraction before and after cyclic loading was measured using a material testing system. Microstructural damage caused by transfixation pin insertion was evaluated by scanning electron microscopy.


RESULTS
The temperature following pin insertion was significantly higher for SDST transfixation pins. Periosteal surface cortical fractures were found in 50% of the bones with SDST transfixation pins and in none with NDNT transfixation pins. The NDNT transfixation pins were significantly more resistant to axial extraction than SDST transfixation pins. Grossly and microscopically, NDNT transfixation pins created less damage to the bone and a more consistent thread pattern.


CONCLUSIONS
In vitro analysis revealed that insertion of NDNT transfixation pins cause less macroscopic and microscopic damage to the bone than SDST transfixation pins. The NDNT transfixation pins have a greater pull out strength, reflecting better initial bone transfixation pin stability.
Morisset
S
S
Department of Veterinary Clinical Sciences, Purdue University, West Lafayette, IN 47907-1248, USA.
McClure
S R
SR
Hillberry
B M
BM
Fisher
K E
KE
D000818:Animals; 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