Date of Award


Document Type


Degree Name

Master of Science (MS)


Biomedical Engineering



Research Advisor

Brooke A. Sanford, Ph.D.


William M. Mihalko, Ph.D. John L. Williams, Ph.D.


ACL reconstruction, anterior cruciate ligament, joint coordination, stairs, variability, vector coding


Anterior cruciate ligament (ACL) rupture is a common injury, with an estimated incidence of 120,000 to 200,000 per year in the United States. ACL reconstruction surgery is the standard treatment for this injury to restore knee joint stability and function. While surgical reconstruction has been shown to restore laxity of the knee, current literature lacks consensus on return to normal knee joint kinematics following surgery. Additionally, re-injury is a major risk for those who return to sports activity after reconstruction surgery. Dynamical systems methods for quantifying joint coordination variability have been explored as a method for detecting differences between ACL reconstructed (ACLR) subjects and healthy control subjects. Specifically, altered joint coordination variability has been linked to lower extremity instability, which may indicate re-injury risk.

The aim of this study was to assess joint coordination and joint coordination variability using a vector coding technique in ACLR subjects after recovery and return to normal activity. Our hypothesis was that joint coordination variability of ten selected intra-limb knee-knee and knee-hip couplings would be altered in the ACLR group compared to a group of healthy control subjects based on previous findings using similar methods.

Thirty subjects (15 ACLR and 15 normal) were analyzed using a motion capture camera system and force plates. Subjects were asked to ascend a staircase in a step-over-step manner at a self-selected pace, turn around on the elevated platform, then descend from the platform down the steps and return to the starting location. We employed a vector coding method using a custom Matlab script to measure coupling angle variability of knee-knee and hip-knee coupled motion during the stair activity. Individuals with ACLR were found to have differences in joint coordination variability (both increased and decreased) in 5 of the 10 joint couplings analyzed as compared with a healthy control group during the stair descent activity.

The majority of differences were found to be reductions in variability in the ACLR group as compared with controls. It is believed that there is an optimal amount of variability in any motor system that differentiates between the ability to adapt to environmental instability and the risk for injury. Reduced joint coordination variability indicates avoidance of a particular movement and results in the inability to adapt movement strategies in a dynamic environment. Decreased variability in ACLR subjects has also been linked to re-injury in at least one prospective study. These results combined with previous works provide insight into coordinative function after ACLR and may be useful in improving rehabilitation protocols following surgery as well as identifying those at risk of re-injury.