High-speed subfailure stretch of rabbit anterior cruciate ligament: changes in elastic, failure and viscoelastic characteristics

Objective. To study alterations in the ligament mechanical characteristics due to a subfailure stretch delivered at high speed. Design. An in vitro study of rabbit anterior cruciate ligaments. Background. Although ligamentous sprains occur more frequently than the complete failures, only a few biomechanical studies have investigated the effects of such injuries. Purpose of the study was to document changes in elastic, failure and viscoelastic properties of a ligament that had been subjected to a high-speed subfailure stretch. Methods. Thirteen paired fresh adult rabbit femur-anterior cruciate ligament-tibia preparations were used. One ligament of each pair (control) was subjected to two relaxation tests and then stretched until failure. The other ligament (experimental) was subjected sequentially to relaxation test, subfailure stretch (80% of the failure deformation of the control), relaxation test, and then stretched until failure. Load–deformation curve until failure was characterized by nine parameters, which included failure force, deformation and energy absorbed, and deformations measured at various load values, and stiffness. Relaxation curve was parameterized by five relaxation forces measured at 10, 30, 50, 130, and 180 s. Results. Due to subfailure stretch, there were no changes in failure force and stiffness, while deformations increased, and energy absorbed and relaxation forces decreased. Conclusions. The 80% subfailure stretch delivered at high speed increased the deformations in load–deformation tests, and decreased the forces in relaxation tests.