Triple arthrodesis: a biomechanical evaluation of screw versus staple fixation

The subtalar, talonavicular, and calcaneocuboid joints were internally fixed to simulate triple arthrodesis was performed on eight matched pairs of human cadaver feet. Feet were randomly assigned such that one specimen in each pair was internally fixed with cobalt-chrome staples and one specimen with stainless steel screws. Liquid metal strain gauges were placed in a perpendicular fashion across the three joints of each specimen. Each foot was then secured to the Shore Western Materials Test System where a series of 10 increasing eversion stresses across the foot was created. Displacement was measured at each joint with every increase in eversion stress. Our results show that there is no statistical difference in fixation strength between screws and staples at the talonavicular, calcaneocuboid, or subtalar joints (P = 0.862). Although many studies determining the strength to failure of different implants have been performed, shear stress and micromotion at the joint surfaces have not been evaluated, to our knowledge, and no single implant in this study has shown superior immobilization characteristics to recommend its use as the implant of choice in triple arthrodesis.