Finite Element Analysis of Six Transcortical Pin Parameters and Their Effect on Bone-Pin Interface Stresses in the Equine Third Metacarpal Bone.

Objective:  The objectives of this study were to validate a finite element model of the equine distal limb transfixation cast and to determine the effect of six transcortical pin parameters on bone-pin interface (BPI) stresses in the third metacarpal bone.

Study Design:  A transfixation cast finite element model was developed from a computed tomography scan of the third metacarpal bone and modelled pin elements. The model was validated by comparing strain measured around a 6.3-mm transfixation pin in the third metacarpal bone with the finite element model. The pin parameters of diameter, number, location, spacing, orientation and material were evaluated by comparing a variety of pin configurations within the model.

Results:  Pin diameter and number had the greatest impact on BPI stress. Increasing the diameter and number of pins resulted in lower BPI stresses. Diaphyseal pin location and stainless-steel pins had lower BPI stresses than metaphyseal location and titanium alloy pins, respectively. Offset pin orientation and pin spacing had minimal impact on BPI stresses during axial loading.

Conclusion:  The results provide evidence that diameter and number are the main pin parameters affecting BPI stress in an equine distal limb transfixation cast. Configurations of various pin size and number may be proposed to reduce BPI stresses and minimize the risk of pin related complications. Further refinement of these models will be required to optimize pin configurations to account for pin hole size and its impact on overall bone strength.