Strength of wired sternotomy closures: effect of number of wire twists

The objective of this study was to investigate the effect of the number of wire twists on the strength of wired sternotomy closures. A custom-built test rig, fitted to a materials testing machine, was used to apply an increasing tension to wire closures, until they failed. The number of twists in the wire closure was varied between one and ten. Stainless steel wires of diameter 0.7 mm (No. 5) and 0.9 mm (No. 7) were tested. Initially, there is an increase in the maximum strength of the wire closure with increasing number of wire twists. After three wire twists greater strength is not achieved with increasing the number of wire twists. The highest mean force taken by the 0.7 mm diameter wire was 613 N ( approximately 63 kg), at nine wire twists, whereas the highest force taken by the 0.9 mm diameter wire was 887 N ( approximately 90 kg), at eight wire twists. However, by three wire twists, 80% and 88% of the maximum force has been achieved for the 0.7 and 0.9 mm diameter wire, respectively. Twisting wires many times in a sternotomy closure does not result in increased strength. Three or four twists would appear sufficient to sustain the forces across a sternotomy.