An in vitro biomechanical comparison of two fixation methods for transverse osteotomies of the medial proximal forelimb sesamoid bones in horses.
OBJECTIVE
This study compared the mechanical properties of the normal intact suspensory apparatus and two methods of fixation for repair of transverse, midbody fractures of the proximal sesamoid bones of adult horses: transfixation wiring (TW) and screws placed in lag fashion (LS).


METHODS
An in vitro, paired study using equine cadaver limbs mounted in a loading apparatus was used to test the mechanical properties of TW and LS.


METHODS
Seventeen paired (13 repaired, 4 normal) equine cadaver limbs consisting of the suspensory apparatus third metacarpal bone, and first and second phalanges.


METHODS
The two methods of repair and normal intact specimens were evaluated in single cycle-to-failure loading. Yield failure was defined to occur at the first notable discontinuity (>50 N) in the load-displacement curve, the first visible failure as evident on the videotape, or a change in the slope of the moment-fetlock angle curve. Ultimate failure was defined to occur at the highest load resisted by the specimen. Corresponding resultant force and force per kg of body weight on the suspensory apparatus, fetlock joint moment, and angle of fetlock dorsiflexion were calculated by use of specimen dimensions and applied load. These were compared along with specimen stiffness, and ram displacement.


RESULTS
Load on the suspensory apparatus, load on the suspensory apparatus per kg of body weight, moment, applied load, and angle of fetlock dorsiflexion at yield failure were significantly greater for the TW-repaired than for the LS-repaired specimens. A 3 to 5 mm gap was observed before yield failure in most TW-repaired osteotomies.


CONCLUSIONS
Transfixation wiring provided greater strength to yield failure than screws placed in lag fashion in single cycle load-to-failure mechanical testing of repaired transverse osteotomized specimens of the medial proximal forelimb sesamoid bone.
Wilson
D A
DA
Department of Veterinary Medicine, University of Missouri, Columbia 65211, USA.
Keegan
K G
KG
Carson
W L
WL
D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000662:veterinary; D001864:Bone Wires / Q000662:veterinary; D002102:Cadaver; D005552:Forelimb / Q000293:injuries / Q000502:physiology; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000662:veterinary*; D050723:Fractures, Bone / Q000601:surgery / Q000662:veterinary*; D006736:Horses / Q000293:injuries*; D016268:Internal Fixators / Q000662:veterinary*; D010027:Osteotomy / Q000662:veterinary; D012716:Sesamoid Bones / Q000293:injuries* / Q000502:physiology; D014743:Videotape Recording