Author ORCID Identifier

Date Available


Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation


Health Sciences


Rehabilitation Sciences

First Advisor

Dr. Gilson Capilouto

Second Advisor

Dr. Phillip Gribble


Over 100,000 anterior cruciate ligament reconstructions (ACLR) occur annually in the United States, with one in four individuals sustaining a second injury within the first two years after reconstruction. Due to the proprioceptive nature of the anterior cruciate ligament, the lack of regaining postural control and balance are likely large contributors to the rate of secondary injuries after ACLR. Recent literature has identified cerebral changes after anterior cruciate ligament injury and surgery, likely due to altered sensation and feedback loops. However, no study thus far has investigated the neurological feedback loops that may place this group at higher risk of injury than their healthy peers.

The purpose of this dissertation was to investigate neuromotor feedback loops, including knee extensor submaximal steadiness, time to stabilization, long latency response, and center of pressure stability. Both limbs of the ACLR cohort were compared to a cohort of healthy control subjects.

Participants: Fifty individuals who were six-months after a primary anterior cruciate ligament reconstruction were recruited for testing. All subjects had surgery by one of three surgeons at the University of Kentucky, and received rehabilitation following their surgery. The healthy control cohort was recruited as a sample of convenience, with an attempt to match the injured cohort in age, height, mass, and activity level. Healthy subjects had no history of a previous lower extremity surgery and had no history of an injury that resulted in gait abnormalities. All data were collected between December of 2018 and January of 2020.

Methods: Subjects attended the University of Kentucky Biomotion Laboratory their sixth month after an ACL reconstruction. Isometric Biodex strength testing was performed at a maximal and submaximal level, with the knee placed in 90 degrees of flexion. Eight electromyography sensors were placed prior to the motion capture data collection. Subjects performed three successful maximum forward and backward hops with a 5-second hold. Subjects then underwent a push-and-release test in the backward direction, where subjects had to regain their balance in five of the ten trials.

Main Outcome Measures: Knee extensor rate of torque development, knee extensor coefficient of variance, time to stabilization, long latency response, and center of pressure jerk.

Statistical Analysis: A one-way ANOVA compared the ACLR limbs and the left limb of the healthy cohort. Bonferroni post hoc testing identified differences between legs. Pearson correlation coefficients assessed how each element of postural stability related to the control of landing a hop, measured through the center of pressure jerk.

Results: Subjects after ACLR displayed decreased control of muscular stability as well as decreased dynamic control as compared to healthy controls, with greatest impairments found in the involved limb. Neuromuscular feedback loops and postural control have not normalized 6-months after ACLR.

Conclusion: While postural control improved following ACLR, it has not normalized 6-months after ACLR. Rehabilitation techniques should focus not only on motion and strength impairments, but also facilitating normalized dynamic postural control.

Digital Object Identifier (DOI)

Funding Information

This research was supported by the Endowed University Professor in Health Sciences’ College of Healthy Sciences Pilot Funding Grant (December 2018-June 2019) and the American College of Sports Medicine (ACSM) Foundation Doctoral Student Research Grant (July 2019-May 2020).