An in vitro biomechanical investigation of an MP35N intramedullary interlocking nail system for repair of third metacarpal fractures in adult horses.
OBJECTIVE
To compare monotonic mechanical properties of gap-ostectomized third metacarpal bones (MC3) stabilized with an MP35N interlocking nail system with contralateral intact bones.


METHODS
Twenty-four pairs of cadaveric equine MC3s.


METHODS
Third metacarpal bones were divided into 4 mechanical testing groups (6 pairs per group): compression, palmarodorsal (PD) and mediolateral (ML) 4-point bending, and torsion. One MC3 from each pair was randomly selected as an intact specimen, and the contralateral gap ostectomized bone was stabilized with a 4-hole, 14-mm-diameter, 250-mm-long, MP35N intramedullary nail, and four, 7-mm-diameter, 60-mm-long MP35N interlocking screws (constructs). Mechanical testing properties were compared between intact specimens and constructs with a paired t test (significance set at P <.05).


RESULTS
Intact specimens were significantly stronger and stiffer than constructs in all testing modes except PD bending. Constructs achieved mean yield strengths that were 57% (compression), 81% (PD bending), 68% (ML bending), and 78% (torque) of intact specimens. Constructs achieved mean stiffnesses that were 53% (compression), 58% (PD bending), 41% (ML bending), and 47% (torque) of intact specimens.


CONCLUSIONS
Monotonic yield mechanical properties of MP35N intramedullary interlocking nail-stabilized, gap-ostectomized MC3 were lower than those of paired intact bones but exceeded reported in vivo loads for dorsopalmar bending and compression and estimated in vivo torsional loads.


CONCLUSIONS
Considering the benefits associated with intramedullary interlocking nail fixation of fractures, this system should be considered for use for repair of MC3 fractures with applicable fracture configurations.
Galuppo
Larry D
LD
J. D. Wheat Veterinary Orthopedic Research Laboratory, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, CA 95616, USA.
Stover
Susan M
SM
Aldridge
Amanda
A
Hewes
Christina
C
Taylor
Kenneth T
KT
D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000662:veterinary*; D002102:Cadaver; D004867:Equipment Design / Q000662:veterinary; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000601:surgery / Q000662:veterinary*; D006736:Horses / Q000293:injuries / Q000601:surgery*; D008663:Metacarpus / Q000293:injuries / Q000601:surgery*; D011859:Radiography; D011897:Random Allocation