Twist Knot Cerclage Wire: the Appropriate Wire Tension for Knot Construction and Fracture Stability

OBJECTIVE: The aim was to find the best wire tension in order to permit a reliable first twist and simultaneously provide the best stability of fracture fixation from the twist knot cerclage wire. DESIGN: Wires at different distal tensions, looped around the fracture, were measured during twist and compared with the yield strength of the wire. Then, the fracture stability of the twist knot cerclage wire was determined from the pull-out strength. METHODS: In order to measure wire tension during twist knot construction, an instrument was designed using the tension load cell of a universal testing machine, a 15 degrees oblique osteotomy femoral shaft and 1.25 mm diameter wire. A wire tensioner and a pair of extraction grips were then used for measuring the pull-out strength of the cerclage wire fixation. RESULT: Three wire tensions (160, 200 and 240 N) were used as looped wire for the first twist knot construction. The 200 N tension cerclage wire provided the best fracture stability. CONCLUSION: It was found that 200 N was the best wire tension for the construction of a twist knot cerclage wire. RELEVANCE: When a cerclage wire is twisted at a femoral shaft using 1.25 mm diameter wire, a wire tension of 200 N should be used to achieve a reliable first twist and the best stability of fracture fixation.