INTER-SEGMENT COORDINATION VARIABILITY POST ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION SEPTEMBER 2015 DEVIN K. KELLY, B.S., UNIVERSITY OF MASSACHUSETTS AMHERST M.S., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Dr. Joseph Hamill There is an increased risk for ipsilateral graft rupture and contralateral ACL rupture following ACL reconstruction surgery (ACLR) despite return to sport clearance. The reason for this increased risk is not well understood. Previous literature has shown that decreased coordination variability is indicative of an injured system regardless of the absence of pain. PURPOSE: To quantify inter-segment coordination variability during three portions of the stance phase of gait in athletes at three progressive time points post-surgery compared to the contralateral limb (NI) and healthy controls. METHODS: Three-dimensional kinematic and kinetic data were collected for 10 ACLR and 10 healthy athletes matched for age, gender, and activity level. The ACLR group was measured at 4 weeks, 12 weeks, and when cleared to run post-surgery. Kinematic data were used in a modified vector coding technique to determine inter-segment coordination variability of lower extremity couples of interest. Statistical significance was determined using two factor multivariate ANOVAs (limb x visit) for early (1-33%), mid (34-66%), and late (67-100%) stance with alpha level set at .05. Tukey post-hoc tests were performed where appropriate. RESULTS: ACLR athletes have decreased inter-segment coordination variability of the involved lower extremity during the late stance phase of gait compared to both the contralateral limb and healthy controls at 4 weeks post-surgery. By 12 weeks post-surgery there were improvements in joint function as exemplified by inter-segment coordination variability of the ACLR involved limb becoming similar to the healthy control limb. CONCLUSION: Inter-segment coordination variability during late stance in the present study is not an indication for the increased risk for ipsilateral graft rupture and contralateral ACL rupture in ACLR athletes.