Knee Stabilisation Strategies During an Isometric Weight-Bearing Force-Matching Task in Males and Females After ACL Injury
Creators: name: Del Bel, Michael
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2017
Subjects: neuromuscular control
anterior cruciate ligament injury
knee rehabilitation
sex differences

description: The anterior cruciate ligament (ACL) plays an important role in knee joint stability, and unfortunately is one of the most commonly injured knee joint structures. The muscles surrounding the knee are also critical for stabilising the knee joint and their activations are altered following ACL injury. Despite the fact that ACL injuries are up to 8 times more likely to occur in females compared to males, there is limited research evaluating the effects of sex on how ACL-deficient individuals adjust neuromuscular control strategies during varying loading conditions. In order to have clinicians implement optimal rehabilitation strategies for ACL-deficient males and females, it is crucial to understand the adaptive functional strategies that are taking place once an ACL injury has occurred. The purpose of this thesis was therefore to provide objective and quantitative measurements describing the functional roles of muscles surrounding the knee. This was accomplished and outlined in this thesis through two chapters in manuscript format and summarised below. i) Sex and ACL-deficiency influence functional muscle roles during an isometric, weight-bearing, force-generation task First, the functional roles of muscles were quantified through the assessment of muscle activations during a series of multi-directional force-production tasks in ACL-deficient males and females while weight bearing. A highly controlled, isometric, force-matching task, whereby participants modulated ground reaction forces in various combinations of sagittal and frontal plane loads was used to quantify force-generation strategies (muscle activations and functional role) of the knee joint. Mean activation magnitudes and profile patterns from 10 muscles in the lower extremity (rectus femoris, vastus lateralis, vastus medialis, biceps femoris, semitendinosus, lateral gastrocnemius, medial gastrocnemius, tensor fascia latae, adductor muscle group, and gluteus medius) were recorded using wireless electromyography (EMG) sensors. Their activations were quantified with an orientation analysis to determine if differences in functional muscle roles existed between four groups; healthy female controls, healthy male controls, ACL-deficient females, and ACL-deficient males. Overall, different functional muscle roles were found between groups. Healthy male controls activated their muscles the most specifically; females with ACL-deficiency activated their muscles the least specifically, while healthy female controls and males with ACL-deficiency shared similar functional muscle roles. This suggests that there was a specificity hierarchy in the ability, or efficiency, to modulate the activation of muscles about the knee joint when exposed to various directional loading conditions. ii) Associations between subjective measures of knee dysfunction and measures of ground reaction forces in ACL-deficient males and females Correlational relationships were evaluated between perceived knee joint function and functional capacity of the knee joint. These relationships were calculated between patient reported outcome measures (PROM) from commonly used knee assessment scoring scales maximal generated forces in the sagittal and frontal planes. Both ACL-deficient groups had significantly lower perceived knee joint function compared to healthy controls. A trend towards significance was observed in the ability to generate maximum forces in the sagittal and frontal planes, with ACL-deficient females generating smaller maximal posterior GRFs compared to healthy females. Only two statistically significant correlations (both for ACL-deficient females) were found between maximal medial GRFs and patient reported outcome measures from the Lysholm and Tegner scoring scales. This indicates that there may be a discrepancy in the sensitivity of subjective outcome measures between sexes and their corresponding ability to generate maximum GRFs. In conclusion, sex differences exist in subjective outcome measures and the functional strategy of neuromuscular control of the knee joint both before and after ACL-injury. The results of this thesis indicate the need for sex-specific tailoring of rehabilitation programs, thus providing an opportunity to improve the success rate of rehabilitation following ACL-injury. Moreover, sensitivity of subjective outcome measures and their relation to simple, practical, functional tasks between sexes warrants further investigations.