Stiffness and permanent deformation of extra-articular distal tibia fractures treated with unreamed small diameter intramedullary nailing

Extra-articular fractures of the distal tibia are increasingly treated using intramedullary nailing. Due to the high load on the system and the long time of loading, fatigue phenomena have to be considered. The aim of this study is to assess the fatigue strength of the system, especially of the distal and proximal interlocking screws. Measurements were carried out using synthetic tibia bones and nails of 4 different producers. Fatigue testing was performed in three sequential stages of increasing load simulating loading during the first 6 weeks after implantation, technical loading and failure loading. The implants were characterized using the parameters stiffness, permanent deformation (including damage) and cycles to screw-failure. The results show, that highest stresses and therefore first screw damage occurred at the proximal interlocking screws. Screw-failure was observed earlier in cannulated nails and if oblique screws were used proximally.