DIAPHYSEAL STRUCTURAL-PROPERTIES OF EQUINE LONG BONES

We evaluated the single-cycle structural properties for axial compress ion, torsion, and 4-point bending with a central load applied to the c audal or lateral surface of a diaphyseal segment from the normal adult equine humerus, radius, third metacarpal bone, femur, tibia, and thir d metatarsal bone. Stiffness values were determined from load-deformat ion curves for each bone and test mode. Compressive stiffness ranged f rom a low of 2,690 N/mm for the humerus to a high of 5,670 N/mm for th e femur. Torsional stiffness ranged from 558 N.m/rad for the third met acarpal bone to 2,080 N.m/rad for the femur. Nondestructive 4-point be nding stiffness ranged from 3,540 N.m/rad for the radius to 11,500 N.m / rad for the third metatarsal bone. For the humerus, radius, and tibi a, there was no significant difference in stiffness between having the central load applied to the caudal or lateral surface. For the third metacarpal and metatarsal bones, stiffness was significantly (P < 0.05 ) greater with the central load applied to the lateral surface than th e palmar or plantar surface. For the femur, bones were significantly ( P < 0.05) stiffer with the central load applied to the caudal surface than the lateral surface. Four-point bending to failure load-deformati on curves had a bilinear pattern in some instances, consisting of a li near region at lower bending moments that corresponded to stiffness va lues from the nondestructive tests and a second linear region at highe r bending moments that had greater stiffness values. Stiffness values from the second linear region ranged from 4,420 N.m/rad for the humeru s to 13,000 N.m/rad for the third metatarsal bone. Differences in stif fness between nondestructive tests and the second linear region of des tructive tests were significant (P < 0.05) for the radius, third metac arpal bone, and third metatarsal bone. Difference between stiffness va lues of paired left and right bones was not detected for any test. Fou r-point bending ultimate failure bending moments ranged from 260 N.m f or the femur to 940 N.m for the third metatarsal bone. There was no di fference in failure bending moment between the directions of applied c entral load for a given bone.