Abstract
The lower limb is the most frequently injured location in Rugby Union, resulting in significant injury burden to professional teams. In order to inform risk mitigation strategies, investigation of the aetiology of high burden lower limb injuries is required. However, sports injury aetiology is a complex problem that is dependent on a multitude of causal factors. The aim of the thesis was to advance knowledge of high burden knee ligament and hamstring injury aetiology in male professional rugby union players, by prospectively exploring the association between injury and selected intrinsic and extrinsic variables.
The first experimental study of the thesis (Chapter Three) illustrates that over a period of seven playing seasons, injuries to the lower limb placed the highest burden on the rugby team participating in the research project, compared to the upper limbs, trunk, head and neck. of these injuries, the locations resulting in highest injury burden were to the knee ligaments and the hamstrings. Specifically, injuries to the anterior cruciate ligament (ACL) sustained during contact events were infrequent but resulted in the highest severity. Injuries to the medial collateral ligament (MCL) sustained during tackle events and rucking placed a high injury burden due to a high incidence rate combined with moderate magnitudes of injury severity. Finally, biceps femoris strain sustained during running was the most frequently occurring injury. The findings of the study provided a focus for the subsequent experimental chapters. Chapter Five demonstrates that isokinetic measures of hamstrings and quadriceps strength have poor predictive value in relation to hamstring strains (the highest AUC score being 0.57), despite being associated with an increased odds of sustaining semimembranosus and semitendinosus strains. Isokinetic strength variables were not associated with sustaining biceps femoris strains. Previous injury to the hamstrings was observed to be associated with an increased odds of subsequent hamstring injury when all muscles were pooled. Previous injury to either the MCL or lateral ankle ligaments was associated with an increased risk of biceps femoris injury and medial hamstring injury. This investigation also identified that chronic exposure of high magnitudes was associated with an increased risk of hamstring injuries sustained during running, specifically exposure to high-speed running over 14 and 21 days prior to the week in which the injury was sustained. Chapter 6 examined a variety of variables which were theoretically associated with contact ACL and MCL injury aetiology. The influence of previous injury history was examined in relation to contact MCL and ACL injury aetiology. Previous knee ligament injury not associated with an increased risk of sustaining a subsequent knee ligament injury during a contact event. However, previous hamstring and triceps surae muscle strains were associated with an increased risk of injury. Isokinetic assessment of both hamstring and quadriceps strength exhibited poor predictive ability in relation to contact knee ligament injury (highest AUC = 0.57). Chapter 6 also examined contact MCL and ACL injury aetiology in relation to lower limb biomechanics during a single-leg drop jump task. Both larger magnitudes of external knee abduction moment and hip adduction moment 50 ms post ground contact were associated with an increased risk of injury. The study highlighted the importance of modelling injury as a rare event in relation to analysis involving player workloads. A minority oversampling algorithm was used to mitigate the negative effects of class imbalance within the player-workloads data sets. Exposure to tackle events during a match was not related to sustaining an MCL or ACL injury from a tackle. When tackle and ruck exposure were combined, increased exposure (during 7 and 14 days preceding the injury) was associated with a decrease in the odds of sustaining a contact MCL or ACL injury where the inciting event involved a tackle or a ruck. Exposure to on-pitch physical activity (PlayerLoadTM) in relation to contact MCL and ACL was also explored. Acute increases in PlayerLoadTM (3-day EWMA and 7-day EWMA) were associated with an increased odds of sustaining MCL injury and ACL injury. Increased magnitudes of chronic PlayerLoadTM exposure during the previous 7-days with a 3-day lag as well as the previous 14-days were both associated with an increased odds of MCL as well as pooled MCL and ACL injury.
In summary, the thesis explores the lower limb injuries which place a high burden on male professional rugby players in addition to a selection of variables that are associated with their aetiology. The injuries that placed the highest burden were knee ligament injuries (MCL and ACL) sustained during contact as well as hamstring strains. The experimental chapters reinforce the importance of previous injury history in relation to injury aetiology, with previous injury to the proximal and distal tissues of the injured area increasing subsequent injury risk, suggesting that a more universal approach to rehabilitation may be required. The findings also demonstrate that isokinetic assessment of hamstring and quadriceps strength exhibits poor classification performance in relation to hamstring, MCL and ACL injury and should not be used to infer the subsequent risk of these injuries. In contrast, joint moments occurring at the early stages of ground contact during a single-leg drop-jump task are better at classifying knee ligament injury suggesting more dynamic tasks are required when investigating sports injury aetiology. Finally, the thesis explores the influence of player workloads in relation to injury aetiology, and highlights that the differences in this relationship depending on the injured tissue type as well as the data collection methodology. The studies within the thesis are some of the first to be conducted within a rugby union setting, with this in mind, the work within the thesis provides a conduit between epidemiological and mechanistic studies in addition to providing practical applications for men’s’ professional rugby teams.