Do K-wires made from shape memory alloys increase pull-out forces? A preliminary experimental cadaver study in bovine bone.

After osteosynthesis of the proximal humerus by Kirschner wires (K-wire), loosening and secondary loss can occur. This study tested primary fixation of wires made from a shape memory alloy (SMA) Nitinol (NiTi), compared to conventional steel K-wires by pull-out tests. Blocks of cancellous bone were tested with three wire types: NiTi-K-wire with split apex geometry and conventional steel K-wires with and without threads. We found that NiTi-wires can be pulled out of bone more easily than steel wires (P=0.05), even though the former had rougher surfaces. The application of NiTi-wires through bone produced no better stability in comparison to normal steel K-wires, because of triggering the memory effect. Further studies are required to determine if NiTi wires of another appropriate design, surface and localization are superior to conventional wires in the context of this application.