Development and Application of the Pelvic Tracker

Abstract

Backpacks are commonly used by students of all ages and there has been a growing concern in many countries in relation to the backpack loads carried by school children and its association with the rise in complaints of neck, shoulder and back pain. Of further concern is the work of Hestbaek et al. (2006) which has shown a correlation between experiencing back pain as an adolescent and experiencing low back pain as an adult. In recent years, a number of studies have investigated physiological and movement kinematic responses to load carriage, such as oxygen consumption, heart rate, gait pattern and trunk posture (Hong et al., 2000; Pascoe et al., 1997). However, most of the studies that focused on children carrying loads looked only at gait patterns and trunk and neck postures. None of the previous studies investigated the compensatory pelvic motions of school children due to increased loads. Also, it was reported that one of the major limitations of measuring pelvic kinematics whilst carrying a backpack was occlusion of retro-reflective markers, and consequently this limits the type of activity and subject to be measured using an optical motion tracking system. Despite the presence of a variety of models, there are still debates on their reliability and repeatability, and consequently there is no clearly defined standard or consensus. In this thesis, a novel methodology was developed to measure pelvic kinematics. Its repeatability and reliability was validated experimentally by comparing it to the most relevant previous method. The result of this experiment showed that the new method improved the repeatability, reliability and reproducibility of kinematics data of the pelvis and overcomes a number of theoretical and experimental limitations, such as marker occlusion. The validated method was used to develop a protocol to measure the pelvic kinematics in adolescents whilst carrying loaded backpacks of 17% and 25% of their body weight during different activities of daily living on the basis of a survey which was conducted to explore the average daily weight that children carry to school in the UK. The result of this experiment revealed that as the load increased to 25% of the body weight, the instability in postural control increased and significant changes in pelvic tilt and rotation were noted in almost all activities. It was revealed in this study that female and male subjects used different mechanism to compensate for the effect of a heavy backpack. It was evident that carriage of loaded backpack will result in alteration of the movement of the pelvis and may in future promote postural deviation and increase lower back pain.