A Comparison of Methods for Measuring Damage in Sucrose-Treated Medial Collateral Ligaments

The knee is the most complex joint in the human body. It consists of a system of muscle, bone, and ligaments that endures repetitive loading during daily and athletic activities. When this loading is excessive, damage  to the knee occurs leading to a decreased quality of life.The medial collateral ligament (MCL) is one of the 4 major ligaments known to be commonly injured in the knee. The risk of injury to the knee joint increases with the elderly and individuals who experience chronic dehydration. For this reason, the focus of this study is to compare different mechanical quantities that can be used to analyze damage to the MCL.

In this study, a novel mechanical testing protocol is used to progressively induce damage in dehydrated rat MCLs by performing tensile tests. This involves stretching the ligaments along their longitudinal axes to consecutive and increasing displacements starting at a 0.4 mm displacement and in increments of 0.2 mm until complete failure occurs. The load and change in length that the ligament experiences are measured at each displacement. Three different methods were evaluated to determine subfailure and damage propagation in rat MCLs: changes in tangent stiffness and chord stiffness, and changes in the load value at the 0.4 mm displacement for each load-displacement curve. The findings of this study indicate that the tangent stiffness and load at the 0.4 mm displacement provide information of the early onset of damage propagation. The decrease in chord stiffness of the ligament does not indicate damage progression in the ligament, but rather is the sign of the imminent failure of the MCL.This study provides insightful data into understanding the subfailure damage in the MCL.