Effect of elongation rate on the failure properties of the rabbit anterior cruciate ligament

The effect of elongation rate on the failure properties of the rabbit femur-anterior crucicate ligament-tibia were investigated, Paired limbs were elongated to failure at rates of 0.0001 m s(-1) and 0.92 m s(-1). Two distinct types of tibial avulsion injury reflecting rate-dependent areas of weakness were noted. 'Bony avulsions' formed by the junction between cortical and trabecular bone comprised the predominant injury observed at the faster elongation rate. 'Fibrous avulsions' between the zones of mineralized fibrocartilage and bone occurred predominantly at the slower elongation rate. The faster rate significantly increased ultimate load (74%) and stiffness (615%) on average, relative to the slow rate. In contrast to what has been previously described, there was a significant decrease in failure deformation (79%) at the faster rate. Relevance--Our study suggests that within the bone-ligament-bone complex, bone is more sensitive to failure at high elongation rates, and the fibrocartilagenous zone of the ligament is more sensitive to injury at lower elongation rates. In addition, our results indicate that rapid elongation may enhance the viscous behaviour of the collagen matrix and preclude recruitment and straightening of collagen fibres. Consequently, for rapid stretch rates we hypothesize that ligament is vulnerable to failure at much smaller deformations than previously described.