Evaluation of a tapered-sleeve transcortical pin to reduce stress at the bone-pin interface in metacarpal bones obtained from horses.
OBJECTIVE
To evaluate stiffness and bone-pin interface stress for a transcortical tapered-sleeve pin (TSP) that incorporates bilateral tapered sleeves over a transcortical pin.


METHODS
14 third metacarpal bones (MCIII) collected from adult horses of various breeds.


METHODS
Each MCIII was cut in half to provide 2 test specimens. Pins (conventional and TSP) of 3 diameters (6.35, 7.94, and 9.50 mm) were inserted in specimens (3 specimens for each diameter and each type of pin). The test fixture simulated a typical sidebar-span skeletal fixation device for horses. Single cycle load-deflection tests were performed. Cyclic fatigue tests of TSP were performed to evaluate fatigue characteristics and stress conditions at the bone-pin interface. Maximum stress and strain were calculated, and results were compared with existing data on fatigue characteristics of bone.


RESULTS
Significant increases in stiffness (load-deflection) and higher loads at yield point were detected for the TSP (stiffness for conventional 9.50mm pins, 4,500 N/mm; stiffness for TSP, 19,988 N/mm). Results of cyclic tests revealed a close correlation with existing data on fatigue characteristics.


CONCLUSIONS
The TSP described here is stiffer than conventional transcortical pins, and stress across the bone-pin interface is more evenly distributed. Use of this TSP should minimize major problems encountered during external fixation associated with the transcortical pin and bone-pin interface (ie, bone necrosis, infection of the pin track, pin loosening, and bone failure).
Nash
R A
RA
Comparative Orthopedic Research Laboratory, School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, Kennett Square 19348, USA.
Nunamaker
D M
DM
Boston
R
R
D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000662:veterinary*; D005121:Extremities / Q000601:surgery; D005592:Fracture Fixation / Q000379:methods / Q000662:veterinary*; D050723:Fractures, Bone / Q000601:surgery / Q000662:veterinary*; D006734:Horse Diseases / Q000601:surgery*; D006736:Horses; D050279:Metacarpal Bones / Q000293:injuries