Comparison of 3.5- and 4.0-mm Cortical Bone Screws for Stabilization of an Equine Navicular Bone Fracture Model

The aim of this study was to compare the strength (load at failure) and the number of cycles to failure of 3.5- and 4.0-mm cortical screw-bone constructs for repair of navicular bone fractures in horses.This was an in vitro biomechanical study that used a four-point bending apparatus to determine the load at failure of 3.5- and 4.0-mm cortical screw-bone constructs subjected to static and cyclic loading.In static testing, pairwise comparison of 4.0-mm cortical screw-bone constructs demonstrated significantly greater strength (mean increase: +16%, p = 0.0135) compared with those in the 3.5-mm group. In cyclic testing, the mean number of cycles to failure for the 4.0-mm cortical screw-bone construct was not significantly different from that of the 3.5-mm cortical screw-bone construct, due to a high variability in the values.A 4.0-mm cortical screw offers biomechanical advantages over a 3.5-mm cortical screw and may be an alternative implant for the treatment of navicular bone fractures in horses. Further clinical studies are needed to determine whether this screw can also be inserted without complications in vivo.