The anterior cruciate ligament (ACL) stabilizes the knee during various sporting activities and has great importance as the knee relies entirely on the ligaments and muscles for stabilization. The ACL commonly gets injured during sports activities such as basketball, soccer, and football. In the United States over 80,000 ACL injuries occur every year. There has been decades of research performed on ACL injuries regarding the injury mechanisms of non-contact ACL injuries, but yet they are still not well understood. This is mainly because trials and tests cannot be conducted on live subjects to understand the injury mechanisms. Existing in-vivo and in-vitro studies in the literature do not relate the effects of dynamic knee muscle forces and kinematics of sports activities with the strain in the ACL. In this thesis, in-vivo and in-vitro approaches are combined to quantify the effects of muscle group forces on ACL strain during jump landing. This is done by first obtaining muscle force profiles of the knee by performing motion capture and inputting the ground reaction forces and kinematics into a musculoskeletal model. Using the muscle forces and a six axis sagittal plane dynamic knee injury simulator the jump landing simulation can be performed. Six electromechanical actuators controlled by a multi-axis control system apply dynamic muscle forces at the insertion sites of the hamstrings, quadriceps, gastrocnemius, and a hip moment to simulate the hip flexors. The ACL strain is measured using a differential variable reluctance transducer mounted on the ACL. Our results show that the simulator is able to successfully perform jump landing. The muscle force-time profiles tracked the input very well. The ACL strain from our studies fell within a reasonable level compared to data from other studies of jump landing. This simulator has proven to be successful in simulating high-risk motions.

Global decreases in physical activity levels among youth have been observed over the last decade and physical inactivity is one of the major risk factors associated with leading causes of death and disability. Injury has been found to be the most common reason for attrition from lifelong physical activity among young people. This thesis deals with the promotion of physical activity by addressing the prevention of knee injuries among adolescent basketball players. Basketball is currently thought to be one of the fastest growing sports in South Africa, a sport associated with a high knee injury prevalence and consequence of developing early osteoarthritic changes. There are no published reports on knee injury prevalence among African youth, nor is there a national policy on injury prevention as a mechanism for promoting healthy activity. This thesis reports on several interlinked studies which established injury prevalence and mechanisms, investigating the biomechanics of a major injury mechanism, designed and laboratory tested preventative strategy, and then applied this strategy in a pilot field study. / The first stage of this study involved a retrospective survey of young South African basketball players (n=458). A questionnaire captured information on injuries sustained during the previous season. The probability of sustaining a knee injury was significantly greater than sustaining an injury to another body part or no injury combined (OR: 1.3:95% CL 1.1-1.5). The most common injury mechanism among both boys and girls was landing badly from a jump and approximately one third of the knee injuries (37.5%) were sustained as a result of landing badly. / The second stage of the study, a biomechanical analysis of landing strategies of matched knee injured and uninjured adolescent basketball players (n=22) was conducted using a three-dimensional, six-camera Vicon motion analysis system and force plate. The injured and uninjured players were matched for gender, age, anthropometrics, basketball experience and had to play for the same club. A strong positive correlation (0.49: p<0.01) was found between the maximum ground reaction force and the average injury score of the case subjects. The control players had significantly deeper knee flexion angles than the cases on landing (p=0.01). Injured players also demonstrated significantly less eccentric activity on landing compared to the uninjured players (p<0.01). / The third stage of the study was to develop a neuromuscular exercise program to prevent injuries from landing, based on the biomechanical analysis of the landing data. Currently these types of exercise programs have the most promising evidence in the prevention of knee injuries. The rationale of these programs are based on improving feed-forward mechanisms of motor control, thereby decreasing the motor response time, enabling dynamic joint stability to prevent injuries during high speed dynamic tasks such as landing. Biomechanical validation of the resultant exercise program suggested that it would be effective in improving landing technique of uninjured male adolescent basketball players with respect to reducing peak ground reaction forces (p<0.01), improved knee flexion angles (p<0.01) and improved negative work (p<0.01). / The final stage of the project was to employ health promotion principles in an on-field validation of the exercise program and highlighted the complexities of introducing such a program into real-life training situations. The preliminary results from this aspect of the study demonstrated a decrease in knee injury prevalence. The importance of qualitative information in implementing preventative strategies in ensuring the success of the program implementation and compliance from players, coaches and players was also highlighted. / This study proposes recommendations for preventing knee injuries in adolescent South African basketball players and provides ideas for future research into injury prevention in young sports players. / Thesis (PhD)--University of South Australia, 2004.

Thesis (MAppSc in Physiotherapy)--University of South Australia, 1996

Thesis (MAppSc in Physiotherapy)--University of South Australia, 1996

Thesis (MAppSc in Physiotherapy) -- University of South Australia

Thesis (MAppSc) -- University of South Australia, 1998

Thesis (M.App.Sc. in Physiotherapy)--University of South Australia, 1995.

Knee joint osteoarthritis is recognised as a significant subset of osteoarthritis. Little work has examined muscle changes that occur with knee joint osteoarthritis. Much of this work has centred on strength deficits, while little work has examined the effect of joint pathologies, such as osteoarthritis, on the fatigue resistance of the muscles associated with an affected joint. The purpose of this study was to investigate the relative fatigue-resistance characteristics of the vastus medialis in subjects with and without knee joint osteoarthritis, as well as the ability to predict endurance times in these groups, using high spatial resolution electromyography and a sub-maximal isometric endurance test. Twenty-six subjects with unilateral knee osteoarthritis and seventeen subjects with no known knee pathology were evaluated. All subjects performed initial tests to evaluate maximum voluntary contraction (MVC), voluntary activation levels, and true maximum force (TMF). Endurance time was assessed during an isometric quadriceps contraction at 50% of the true maximum force. Surface electromyography (sEMG) data was collected from the vastus medialis muscle of the quadriceps group during the endurance test. MVC tests showed that the affected leg of the group with osteoarthritis was significantly weaker (p < 0.05) than the unaffected leg. Voluntary activation data showed that subjects with osteoarthritis presented with significant bilateral deficits (p < 0.05). TMF data showed a significantly lower (p < 0.05) true potential for force generation in the affected compared to the unaffected leg of the osteoarthritis group. Endurance time data showed no significant difference between groups. Electromyography data showed significant differences (p < 0.05) between the affected and unaffected legs in initial values of Median Frequency (MDF), Mean Power Frequency (MPF) and Conduction Velocity (CV), the percentage change in CV and the relative rate of change in the frequency band between 5 and 30Hz (FB1). Finally, significant correlations were seen between endurance time and the relative rate of change of MDF, MPF and CV calculated over the initial thirty seconds of the endurance test. There were no significant correlations from either leg of the group with knee joint osteoarthritis.It can be concluded from this study that there are differences in strength measures, and in the sEMG signal collected from the vastus medialis muscle of the affected and unaffected legs of subjects with knee osteoarthritis. It appears likely that the differences observed in the sEMG signals were related to a decrease in the representation of type-2 muscle fibres in the vastus medialis of the affected leg. Furthermore, these changes in the behaviour of the signal appear to indicate an improvement in the relative fatigue resistance of the affected leg in relation to the unaffected leg of the group with knee osteoarthritis.Moderate success was seen with the prediction of endurance time in control subjects in the current work using a short duration (30-second) endurance test. This relationship was not seen in either the affected or unaffected leg of the subjects with knee osteoarthritis. Further investigation utilising different sEMG collection and analysis techniques in this area may improve prediction of endurance time in unaffected and affected subjects.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 5 uppsatser.

Thesis (Ph.D.)--University of Western Australia, 2004.