Grace Campbell Thesis Document

Abstract

Is Offloading the Knee During Functional Tasks Predictive of Quadriceps Weakness in Healthy and ACLR Individuals. By Grace Campbell July, 2025

Director of Thesis (or Dissertation): Anthony Kulas Major Department: Kinesiology

ABSTRACT INTRODUCTION: Anterior Cruciate Ligament tears (ACL) are common injuries that often occur in young individuals who participate in cutting and jumping sports. Individuals who suffer from an ACL injury are faced with short and long term-effects in their lives. These individuals typically have a decreased active lifestyle, an increase in medical bills, and run the risk of developing osteoarthritis (OA) at an earlier age. Even after surgery and recovery, individuals who have a reconstructed ACL (ACLR) are 15 times more likely to suffer a second knee injury compared to the risk of a healthy population of athletes sustaining their first ACL injury. Because of the high rates or second injury focus has been put onto the components of the return to sport (RTS) criteria. The RTS is composed of 4 main components: patient reported outcomes, testing of functional movements, quadriceps strength, leg strength symmetry (LSI) within 90%, and time. From those 4 components only time and quadriceps LSI has been shown to be a risk factor of a second ACL injury. Unfortunately, not everyone has the resources, such as a dynamometer, to properly test quadriceps LSI so they rely on a person’s functional ability. As of now functional tests are not predictive but assessing a single leg vertical jump and the way they move during each test may help functional tests be more predictive risk factor. PURPOSE: Determine the effect of knee extensor torque and mechanical work during a single leg vertical jump on quadriceps strength weakness in ACLR individuals. METHODS: 35 total subjects, 16 healthy 19 ACLR were taken through a similar process to an individual testing out of ACL rehab by completing multiple components of the return to sport (RTS) criteria. Each participant completed the Marx’s activity rating scale, Knee osteoarthritis outcome score (KOOS), and the Tampa scale of kinesiophobia (TSK) surveys. To get a strength profile on each participant a series of 3 different strength tests were collected bilaterally on the HUMAC dynamometer. Followed by testing functional performance during a single leg vertical jump (SLVJ) and single leg horizontal jump (SLHJ) completed bilaterally. RESULTS: Significant differences were seen within the ACLR group when comparing the injured limb to the non-injured limb during isokinetic strength testing (p =.048), joint moments at the knee during SLVJ (p =.002) and SLHJ (p =.001) and overall jump height during the SLVJ (p =.003). These differences are not seen within the healthy controls. CONCLUSION: The underperformance in strength and function seen in the ACLR group is more than likely related to a quadriceps weakness and was shown from the performance metrics but also by the way the ACLR group adapted to move by offloading their knee when completing the functional tasks. Clinically the single leg vertical jump may prove to be a better assessment of function compared to the single leg horizontal jump due to the quadriceps effort needed to and the uniform movement pattern used to complete the jump.