Biomechanical evaluation of a newly devised model for the elongation-type anterior cruciate ligament injury with partial laceration and permanent elongation

Objective. To biomechanically evaluate a newly devised model for the elongation-type anterior cruciate ligament injury with partial laceration and permanent elongation. Design. Thirty-six rabbits were randomly divided into 4 groups of 9 animals each, after a quantitative injury was given to the right anterior cruciate ligament. The 4 groups were sacrificed at 0, 6, 12, and 24 weeks after surgery, respectively. Biomechanical and histological evaluations were performed at each period. Background. No adequate animal models have been established for the elongation-type anterior cruciate ligament injury in which the mid-substance is permanently elongated with partial laceration. Methods. The anteromedial and posterolateral half of the anterior cruciate ligament was transected at the proximal and distal one-third levels, respectively. Then, the anterior cruciate ligament was stretched by applying an anterior drawer force to the tibia at 90 degrees of knee flexion. Results. The treatment significantly increased the anterior translation of the knee into approximately 150–250% at each period after surgery. The maximum load and the stiffness of the femur–anterior cruciate ligament–tibia complex significantly decreased to 30% or less immediately after surgery, and then gradually increased to 50% at 12 weeks. Conclusions. In this model, this quantitative treatment created serious injuries with partial laceration and permanent elongation in the anterior cruciate ligament to similar degrees. Also, incomplete tissue healing occurred in the anterior cruciate ligament to similar degrees after the treatment.