This study has addressed the problem of rupture of the anterior cruciate ligament (ACL), one of the most common injuries experienced during sports in the world today. A key consideration in this injury is the gender difference in injury incidence rates, with women having much higher rates.This work was the first to identify a potential mechanism for the non-contact injury of the ACL. The mechanism is associated with a rapid opening of the knee in a valgus direction and helps to explain the gender difference in the incidence of injury. Identification of this mechanism also points to future methods for evaluating patient risk and reducing the risk of injury.

The specific studies in this work addressed the following aspects of non-contact ACL injury. Valgus dynamic alignment during single-limb landing correlated to higher peak external knee abduction moment (p<0.02) than neutral or varus alignment. Constraints on arm position also correlated with increased peak external knee abduction moment (lacrosse:​ p<0.05, football:​ p<0.07). Valgus and varus opening of the knee joint were shown to be very sensitive to initial dynamic alignment using a simulation-based model, but they could be controlled by muscle contraction at the hip.

These studies point to the potential for reducing injury of the ACL with better tools for isolating the injury mechanism and identifying those at elevated risk, and motivated the development of a method for more quantitative tracking of motion without the use of reflective markers. This method was used to track simulated motion of the entire body (25 degrees of freedom) and to track real motion of one leg (8 degrees of freedom). Results compared well to data collected using an opto-electronic system with 6 markers.

Future application of the methods developed and further investigation of the mechanism of injury described in this work have the potential to reduce non-contact injury by identifying individuals at elevated risk and training methods to reduce the risk of injury