Force relaxation and sprinback of novel elastic orthopedic cables

Cerclage cables have proven to be very useful in the orthopedic field for bones stabilization and plate fixation but the initial enthusiasm for metallic cables has declined with their high complication rates. Metal materials provide limited elastic deformation compromising their ability to maintain compression. This study compares the mechanical properties of new elastic cables with cobalt-chrome and stainless-steel cables.

Stainless-steel, cobalt-chrome, nylon and nickel-titanium cables were first loaded up to 356 N, then elongation was maintained for 12 hours, next unloaded and finally reloaded to failure. Initial elongation (%), Relative force relaxation (% loss of initial load after a 12h), elastic springback (%) and force to failure (N) were extracted from force-elongation curves.

Initial elongation was the highest for nylon cables (9%), followed by the nickel-titanium (4%) and both metallic cables (0.3%). During 12 hours, no relaxation was observed for the nickel-titanium and the cobalt-chrome cables, whereas 28 and 45% of the tension was lost respectively for the stainless-steel and the nylon cables. The elastic springback of the nickel-titanium and nylon cables (4.4 and 4.7% respectively) was 20 times higher than that of the stainless-steel and cobalt-chrome cables (0.12 and 0.16% respectively). The force to failure of the stainless steel and cobalt-chrome cables was twice that of the nickel-titanium cables.

Multi-braided stainless-steel and cobalt-chrome cables have a high-stiffness with limited ability to tolerate displacement, leading to early cable loosening. Novel low-stiffness cables made of nylon or nickel-titanium offer significant elastic springback improving binding stability.