Investigation of the loss of holding power in the near cortex due to shearing of the bond thread

External skeletal fixation has many uses in the area of orthopedics in both human and veterinary medicine. The success of a procedure utilizing a fixator directly relates to the strength of the pin-bone interface. Prior in vitro study has shown that for a two-cortex, end-threaded pin the far cortex is 1.67 times stronger than the near cortex due to mechanical destruction of the near pin-bone interface. Several factors are believed to contribute to the overall loss of holding power in the near cortex. The purpose of this study was to investigate one area that contributes significantly to the reduction in the near cortex pullout strength, the destruction of the interface due to stripping of the bone threads by the pin as it is temporarily restrained from linear advancement by the far cortex. The results of this study focus attention on the cutting tip of the pin. If the pin can fully engage bone and advance at the rate determined by the threads cut into the near cortex within two and a half pin rotations, the holding power of the near cortex will approach that of the far cortex.