Abstract
A satisfactory method was developed for evaluating the holding characteristics of fasteners in bone. Using this method in over 100 tests, the ultimate pull-out forces and shear stresses were determined for two sizes of sheet-metal type of screws with various interference fits, for a commercial orthopedic self-tapping screw, and for two sizes of machine screws in tapped bone, each at five sections of equine metacarpus. The ultimate pull-out force was maximum at the midlength of the bone, and minimum at the distal end. In general, the failure mechanisms were bone-thread shear for low pull-out forces, bone splitting at intermediate pull-out forces, and bone fragmentation at high pull-out forces. The failure mechanisms of the bone indicate that orthopedic fasteners should possibly not be designed for maximum holding force.
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