Development and application of a measurement method to investigate spinal kinematics during rugby union scrummaging

Abstract

Scrummaging in a game of rugby union occurs after a minor infringement and involves up to eight players from each team pushing against each other to compete for ball possession. The scrum has the greatest propensity for injury compared to all other events in rugby. Injuries affecting the spine of front-row players are of particular concern because these injuries occur frequently and can result in significant pain and functional impairment and, in rare instances, catastrophic consequences. Therefore, identifying potential mechanisms for scrum-related spine injuries is a priority. To develop optimal injury-prevention strategies, it is essential to better understand the biomechanics of the scrum. Kinematic investigations of the spine in front-row players during contested scrummaging could provide important information but these measurements are technically challenging, particularly because of the number of participants involved in the scrum. Given that current methods are not able to measure spinal kinematics during field-based competitive scrums, the aim of this thesis was to develop a method to measure spinal kinematics in front-row players during scrummaging under ecologically valid conditions and begin to investigate the influence of player interactions on spinal kinematics. The novel measurement method was designed using a combination of an electromagnetic motion tracking system and close-range photogrammetry system. To be viable, the measurement method had to (1) require no bulky markers or sensors; (2) be portable to allow field-based measurements; (3) be versatile to allow measurements in any scrum formation and (4) be as reliable and as accurate as traditional measurement methods. The first study evaluated reliability of an electromagnetic motion tracking system for the measurement of cervical spine kinematics during one-man scrums. The second study involved the development of a photogrammetry system, which consisted of five DSLR cameras, to measure thoracic and lumbar spine kinematics and also evaluated reliability and accuracy of this method. The results of the first study indicated reliability of the electromagnetic tracking system was comparable to that of an optoelectronic motion capture system. The second study showed that the photogrammetric system was sufficiently accurate and reliable for the measurement of spinal kinematics during scrums in both laboratory and field environments. Therefore, the findings of these two studies supported the use of the innovative method developed for measuring spinal kinematics during scrummaging. Subsequently, the influence of player interactions during scrummaging was investigated. A series of investigations started with the most simple scrum formation - the one-man scrum. The one-man scrum consists of only one player scrummaging against a static scrum machine and this formation is often used in training sessions to practice the scrum technique. The third study investigated spinal kinematics during one-man scrums to determine basic kinematic patterns, as well as movement variability during the task. The results indicated front-row-players performed the basic scrum technique in a consistent manner, although large within-subject movement variability was found in the sagittal plane for the cervical spine. The difference between cervical spine kinematics during scrums against a scrum machine and against opponents was then investigated in the fourth study. The results revealed that the cervical spine was much more flexed when scrummaging against opponents than when scrummaging against a scrum machine. The fifth study further investigated these cervical spine kinematics during scrums against opponents to determine how different scrum phases affect kinematics. The results showed that impact was the most likely phase to result in traumatic injuries because the cervical spine is considerably flexed, a posture likely to increase the risk of injury. Finally, the sixth study investigated the effect of second-row players on lumbar spine kinematics in front-row players during scrums. The results showed that interactions with second-row players resulted in a substantial decrease of the neutral lumbar lordosis which may result in low back injuries. This series of studies are the first to investigate player interactions on scrum kinematics and collectively the findings suggest that machine-based scrummaging practice should be kept to a minimum given this type of practice has limited potential to prepare players for competitive scrummaging. Moreover, scrum formation should be selected carefully in training and rehabilitation programs to best foster safe and effective scrum technique given interactions between players have significant influence on front-row players' spinal kinematics. This thesis provides an innovative method to facilitate the measurement of spinal kinematics during field-based contested scrums. The findings extend the understanding of kinematics of the cervical and lumbar spine in front-row players during scrums and provides practical information that could be implemented by coaches and those involved in the rehabilitation of players regarding scrummaging technique.