Strain rate effect on the mechanical behavior of the anterior cruciate ligament–bone complex

Traction tests were performed on the bovine anterior cruciate ligament–bone complex at seven strain rates (0.1, 1, 5, 10, 20, 30, 40%/s). Corresponding stress–strain curves showed that, for a given strain level, the stress increased with the augmentation of the strain rate. This phenomenon was important since the stress increased by a factor of three between the tests performed at the lowest and highest strain rates. The influence of the strain rate was quantified with a new variable called the “supplemental stress”. This variable represented the percentage of total stress due to the effect of strain rate. It was observed that at a strain rate of 40%/s, more than 70% of the stress in the ligament was due to the strain rate effect. In fact, the strain rate strongly affected the toe region, but did not influence the linear part of the stress–strain curves. The use of the linear tangent moduli was then not adequate to describe the strain rate effect in the anterior cruciate ligament–bone complex. This study showed that the “supplemental stress” was a synthetic and convenient variable to quantify the effect of the strain rate on the entire stress–strain curves. This quantification is especially important when comparing the mechanical behavior between anterior cruciate ligament and tissues used as ligament graft.