Spinal kinematic variability in people with chronic low back pain

Abstract

Low back pain (LBP) is one of the leading causes of disability globally and chronic non-specific LBP (CNSLBP) accounts for the vast majority of cases. It is widely acknowledged that people with LBP move differently than pain-free individuals. An abundance of research has examined trunk motor control to understand how movement is controlled in the presence of LBP by evaluating both trunk movement patterns and trunk muscle activity. A commonly observed motor adaptation to spinal pain is a change in spine kinematics, such as angular displacement, angular velocity, as well as changes in the variability of these kinematic variables. However, kinematic variability as a motor adaptation to pain in people with CNSLBP has received less attention and still requires further clarification. This thesis presents research to investigate trunk motor adaptations in people with CNSLBP, specifically, by evaluating kinematic variability differences compared to asymptomatic individuals as a critical element of motor performance during repetitive movements. Additionally, the thesis explores factors such as their trunk muscle co-activation patterns and their clinical characteristics in order to gain insights into possible explanations for different movement variability. The first study was a systematic review which confirmed the existence of a different motor pattern in people with CNSLBP, as indicated by differences in spinal kinematic variability compared to asymptomatic individuals during various functional and non-functional repetitive trunk movements. Furthermore, two experimental studies explored the differences in kinematic variability in people with CNSLBP compared to asymptomatic individuals performing two different tasks using the same linear metric to measure variability during repetitive trunk movements. In the second study we applied a novel real-time tracking task using a 3D motion capture system to assess trunk motor control. This study did not reveal any differences in movement variability in CNSLBP people when compared with asymptomatic individuals, however, it showed that movement variability over repeated tracking cycles was associated with the degree of fear of movement in ii people with CNSLBP. Additionally, the response of those with CNSLBP was consistently delayed in tracking the visual feedback compared to the asymptomatic individuals. The third study tested a lifting task reflecting activities of daily living which detected an increase in movement variability in individuals with CNSLBP, despite performing the task within the same spinal range of motion. Moreover, two additional experiments have introduced the novel application of helical axis (HA) parameters as a measure of spinal kinematic variability during repetitive trunk movements. The fourth study tested the use of HA parameters on asymptomatic individuals which revealed its sensitivity to changes in movement plane and movement speed. The first application of this measure on people with CNSLBP was in the fifth study which revealed an increase in spinal kinematic variability compared to asymptomatic individuals during active trunk repetitive movements, irrespective of the speed or direction of movement. In addition, people with a higher fear of movement showed the lowest kinematic variability. Overall, this thesis further highlights the interaction between physical and psychological features of CNSLBP. The thesis offers new insights into how motor adaptations to spinal pain are present, which suggests the need for tailored interventions to address the unique mechanical presentation of each individual with CNSLBP.