The symmetry of the medial collateral and anterior cruciate ligament properties: a biochemical study in the rat hind limb.

The medial collateral (MCL) and the anterior cruciate ligament (ACL) of the rat's knee are frequently used in biomedical research and occasionally in ligament healing studies. The contralateral normal ligament serves as a control. In this study the presence of symmetry in the biomechanical properties of the MCL and the ACL was investigated. Bilateral femur-MCL-tibia and femur-ACL-tibia preparations were obtained from the hind limbs of sixty rats and were subjected to tensile testing to failure under the same loading conditions. Tensile load to failure, stiffness and energy absorption capacity were measured and the mode of failure was recorded. All biomechanical parameters were not significantly different between the two knees of the same animal, although significant individual variation was evident. The most common mechanism of failure was mid-substance tear. Symmetry seems to exist in the biomechanical properties of the MCL and the ACL in the rat knee. When ligament healing is evaluated, increased group size is necessary and the use of a normal control group may be advisable. The contralateral normal knee ligament may serve as a control when the properties of an injured ligament are evaluated and when the parameters of tensile testing failure under similar load conditions are applied.