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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.

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京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第17955号 / 人健博第9号 / 新制||人健||1(附属図書館) / 30785 / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 黒木 裕士, 教授 坪山 直生, 教授 松田 秀一 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

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There is a big risk that neuroreceptors located in the knee, responsible for our proprioceptive ability, are damaged after an anterior cruciate ligament (ACL) injury occurs. This may cause miscommunication between the neuroreceptors and motoric function in the brain. Due to the brains plasticity, it has been shown that brain activity patterns, presented as blood oxygen dependent level-signal (BOLD-signal), achieved from functional magnetic resonance imaging (fMRI) differs between healthy and injured individuals when performing certain tasks involving knee movement. As there is little consensus on how a proprioceptive test should be performed, a unique test were participants uses blindfold during a knee bending exercise was created at U Motion Lab, Umeå University. A Matlab based general user interface (GUI) was created for evaluation of the proprioceptive test. This GUI is communicating with the third party toolbox SPM12 and performs necessary preprocessing fMRI-image steps for statistical analysis and statistical parametric mapping of the BOLD-signal for both a healthy control- and ACL-injured group. The fMRIimages preprocessed by the GUI were generated by a 3 T GE scanner and the motion data was collected using an eight-camera 3D-motion analysis system. Time events for three different tasks was investigated. These were passive resting, memorizing and proprioceptive events. For both the control (5 participants)- and ACL (2 participants) group the main area of brain activation during the proprioceptive tests occurred in the frontal lobe. For the control group, brain activation was found in the cerebellum anterior lobe which is a possible origin for unconscious proprioception. For the ACL group activation was found in the inferior parietal lobule which involves visuomotor integration. Activation was also found in the inferior frontal gyrus which according to previous studies, may indicate risk-taking/”out of character” decisions. The results of this study indicates that the proprioceptive test seems to be a promising tool for evaluation of proprioceptive ability. However, more subjects need to be included to validate the result of this study.

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Anterior cruciate ligament (ACL) injuries are a major problem among female athletes. Screening for the risk of ACL injuries tends to focus on landing tasks, which may be limited in sports where changing direction is the main action involved in noncontact ACL injuries such as soccer. To investigate whether there is a relationship between single-legged landing (SLL), cutting (90° cuts), and pivoting (180° turns) in terms of the characteristics of dynamic valgus. Study Design: Controlled laboratory study. Methods: Twenty female soccer players (mean ± SD: age, 21.0 ± 3.9 years; height, 1.65 ± 0.08 m; mass, 58.4 ± 6.4 kg) performed a minimum of 6 trials of SLL from a 0.3-m drop height and cutting and pivoting all on the right leg. Kinematics and kinetics were calculated from 3-dimensional motion analysis. Results: Strong correlations were found for peak knee abduction angles between tasks (R = 0.63-0.86, P < .01), whereas only moderate correlations between SLL and cutting (R = 0.46, P < .05), cutting and pivoting (R = 0.56, P < .05), and SLL and pivoting (R = 0.43, P > .05) were found between tasks for peak knee abduction moments. Conclusion: The results suggest that female athletes who exhibit poor SLL mechanics perform the same during various changing direction tasks. Clinical Relevance: The results support the use of existing screening tests that involve landing tasks to identify at-risk athletes for noncontact ACL injuries.

Bakgrund: Främre korsbandsskador (ACL-skador) är allvarliga och vanligt förkommande inom idrott, speciellt hos ungdomar i åldrarna 14-19 år. En förhöjd risk för ACL-skador har påvisats för individer aktiva inom fotboll och handboll, vilka är mycket populära sporter världen över. Inom dessa sporter har även kvinnor påvisats ha två till åtta gånger högre risk att drabbas än män. Syfte: Syftet var att undersöka om det fanns någon skillnad i knästabilitet vid en hopp-landningsrörelse mellan tjejer och killar i åldrarna 16-19 år, aktiva inom fotboll och handboll samt att undersöka om det fanns någon skillnad mellan fotbollsspelarna och handbollsspelarna, oavsett kön. Metod: Ett drop jump-test utfördes av 20 ungdomar, aktiva inom fotboll och handboll, medelålder ±SD 17,0 ± 0,9 år. Testerna filmades i frontal- och sagittalplanet och analyserades sedan med hjälp av Landning Error Scoring System (LESS). Post hoc-analyser genomfördes för att kontrollera skillnader i 1) graden av valgusställning i knäleden mellan tjejerna och killarna och 2) graden av knäflexion mellan fotbolls- och handbollsspelarna i landningsmomentet. Ett oberoende student’s t-test användes till de statistiska analyserna och signifikansnivån sattes till p ≤ 0,05. Resultat: Det fanns ingen signifikant skillnad i LESS-poäng mellan tjejerna och killarna (p = 0,694). Fotbollsspelarna hade signifikant lägre LESS-poäng än handbollsspelarna (p = 0,002). Andelen tjejer som uppvisade valgusställning i knäleden under testutförandet var högre än hos killarna. Fotbollsspelarna uppvisade enligt LESS tillräcklig knäflexion i landningsmomentet i högre utsträckning än handbollsspelarna under testutförandet. Slutsats: Ingen signifikant skillnad i knästabilitet och hopp-landningsteknik fanns mellan tjejerna och killarna. Fotbollsspelarna hade signifikant bättre knästabilitet och hopp-landningsteknik än handbollsspelarna. Tjejerna hade en större grad av valgusställning i knäleden vid testutförandet än killarna och handbollsspelarna uppvisade inte lika stor knäflexion som fotbollsspelarna vid testutförandet. Mer forskning krävs inom området för att resultaten ska kunna generaliseras. / Background: Anterior cruciate ligament injuries (ACL-injuries) are serious and common in sports, especially in adolescents between the ages of 14 and 19. An increased risk for ACL-injury has been shown in individuals active in soccer and team handball, which both are popular sports worldwide. Within these sports, women have been proven to have two to eight times greater risk for ACL-injury than men. Aim: The aim was to investigate whether there was any difference in knee stability during a jump-landing movement between girls and boys aged 16-19 years, active in soccer and team handball and also to investigate whether there was any difference between the soccer players and team handball players, regardless of gender. Method: A drop jump test was performed by 20 adolescents, active in soccer and team handball, mean ± SD age 17.0 ± 0.9 years old. The tests were recorded in the frontal and sagittal plane and were then analyzed using the Landing Error Scoring System (LESS). Post hoc analyzes were used to examine differences in 1) the degree of knee valgus alignment between the girls and the boys and 2) the degree of knee flexion between the soccer- and the team handball players in the landing movement. An independent student’s t-test was used in the statistical analysis and the level of significance was set at p ≤ 0.05. Results: There was no significant difference in LESS-score between the girls and the boys (p = 0.694). The soccer players had significantly lower LESS-score (p = 0.002). A higher frequency of the girls displayed a knee valgus alignment during the test compared to the boys. The soccer players displayed according to LESS adequate knee flexion to greater extent than the team handball players did during the test. Conclusion: No significant difference in knee stability and jump-landing technique was found between the girls and the boys. The soccer players displayed significantly better knee stability and jump-landing technique than the team handball players. The girls displayed a greater degree of knee valgus during the test than the boys did and the team handball players displayed a smaller degree of knee flexion then the soccer players did. More research is required within the area to be able to generalize the results.

Background: Joint stability has been experimentally and clinically linked to mechanisms of knee injury and joint degeneration. The only dynamic, and perhaps most important, regulators of knee joint stability are contributions from muscular contractions. In participants with unstable knees, such as anterior cruciate ligament (ACL) injured, a range of neuromuscular adaptations has been observed including quadriceps weakness and increased co-activation of adjacent musculature. This co-activation is seen as a compensation strategy to increase joint stability. In fact, despite increased co-activation, instability persists and it remains unknown whether observed adaptations are the result of injury induced quadriceps weakness or the mechanical instability itself. Furthermore, there exists conflicting evidence on how and which of the neuromuscular adaptations actually improve and/or reduce knee joint stability. Purpose: The overall aim of this thesis is therefore to elucidate the role of injury and muscle weakness on muscular contributions to knee joint stability by addressing two main objectives: (1) to further our understanding of individual muscle contribution to internal knee joint moments; and (2) to investigate neuromuscular adaptations, and their effects on knee joint moments, caused by either ACL injury and experimental voluntary quadriceps inhibition (induced by pain). Methods: The relationship between individual muscle activation and internal net joint moments was quantified using partial least squares regression models. To limit the biomechanical contributions to force production, surface electromyography (EMG) and kinetic data was elicited during a weight-bearing isometric force matching task. A cross-sectional study design determined differences in individual EMG-moment relationships between ACL deficient and healthy controls (CON) groups. A crossover placebo controlled study design determined these differences in healthy participants with and without induced quadriceps muscle pain. Injections of hypertonic saline (5.8%) to the vastus medialis induced muscle pain. Isotonic saline (0.9%) acted as control. Effect of muscle pain on muscle synergies recruited for the force matching task, lunging and squatting tasks was also evaluated. Synergies were extracted using a concatenated non-negative matrix factorization framework. Results/Discussion: In CON, significant relationships of the rectus femoris and tensor fascia latae to knee extension and hip flexion; hamstrings to hip extension and knee flexion; and gastrocnemius and hamstrings to knee rotation were identified. Vastii activation was independent of moment generation, suggesting mono-articular vastii activate to produce compressive forces, essentially bracing the knee, so that bi-articular muscles crossing the hip can generate moments for the purpose of sagittal plane movement. Hip ab/adductor muscles modulate frontal plane moments, while hamstrings and gastrocnemius support the knee against externally applied rotational moments. Compared to CON, ACL had 1) stronger relationships between rectus femoris and knee extension, semitendinosus and knee flexion, and gastrocnemius and knee flexion moments; and 2) weaker relationships between biceps femoris and knee flexion, gastrocnemius and external knee rotation, and gluteus medius and hip abduction moments. Since the knee injury mechanism, is associated with shallow knee flexion angles, valgus alignment and rotation, adaptations after ACL injury are suggested to improve sagittal plane stability, but reduce frontal and rotational plane stability. During muscle pain, EMG-moment relationships of 1) semitendinosus and knee flexor moments were stronger compared to no pain, while 2) rectus femoris and tensor fascia latae to knee extension moments and 3) semitendinosus and lateral gastrocnemius to knee internal rotation moments were reduced. Results support the theory that adaptations to quadriceps pain reduces knee extensor demand to protect the joint and prevent further pain; however, changes in non-painful muscles reduce rotational plane stability. Individual muscle synergies were identified for each moment type: flexion and extension moments were respectively accompanied by dominant hamstring and quadriceps muscle synergies while co-activation was observed in muscle synergies associated with abduction and rotational moments. Effect of muscle pain was not evident on muscle synergies recruited for the force matching task. This may be due to low loading demands and/or a subject-specific redistribution of muscle activation. Similarly, muscle pain did not affect synergy composition in lunging and squatting tasks. Rather, activation of the extensor dominant muscle synergy and knee joint dynamics were reduced, supporting the notion that adaptive response to pain is to reduce the load and risk of further pain and/or injury. Conclusion: This thesis evaluated the interrelationship between muscle activation and internal joint moments and the effect of ACL injury and muscle pain on this relationship. Findings indicate muscle activation is not always dependent on its anatomical orientation as previous works suggest, but rather on its role in maintaining knee joint stability especially in the frontal and transverse loading planes. In tasks that are dominated by sagittal plane loads, hamstring and quadriceps will differentially activate. However, when the knee is required to resist externally applied rotational and abduction loads, strategies of global co-activation were identified. Contributions from muscles crossing the knee for supporting against knee adduction loads were not apparent. Alternatively hip abductors were deemed more important regulators of knee abduction loads. Both muscle pain and ACL groups demonstrated changes in muscle activation that reduced rotational stability. Since frontal plane EMG-moment changes were not present during muscle pain, reduced relationships between hip muscles and abduction moments may be chronic adaptions by ACL that facilitate instability. Findings provide valuable insight into the roles muscles play in maintaining knee joint stability. Rehabilitative/ preventative exercise interventions should focus on neuromuscular training during tasks that elicit rotational and frontal loads (i.e. side cuts, pivoting maneuvers) as well as maintaining hamstring balance, hip abductor and plantarflexor muscle strength in populations with knee pathologies and quadriceps muscle weakness.