A comparison of the torsional performance of stainless steel and titanium alloy tibial intramedullary nails: a clinically relevant approach

In recent years there has been a tendency to design and manufacture intramedullary nails from titanium alloy rather than from stainless steel. The aim of this project was to compare the torsional performance of one manufacturers standard stainless steel and titanium alloy tibial intramedullary nails, using their distal locking screw holes and dedicated cross screws to secure each nail distally. A custom built test rig and materials testing machine were used to determine the torsional rigidity of the nails. Theory was used to calculate the torsional rigidity of the central parts of each nail. From the mechanical testing, the mean torsional rigidity of the titanium alloy nail system was 40.9 N m2 while that of the stainless steel nail system was 34.6 N m2, for all distal interlocking screw positions tested. Based on theoretical calculations the torsional rigidity of the central part of the nail was 83 N m2 for the stainless steel nail and 66 N m2 for the titanium alloy nail. This study shows the importance of using the distal locking screw holes and dedicated cross screws to secure intramedullary nails during mechanical testing so that clinically relevant results are obtained about the whole nail system and not just the nail.