Refining scapulothoracic kinematic measurement and characterising scapulothoracic resting posture in those with and without chronic non-specific neck pain

Abstract

Neck pain is a common and recurrent condition affecting between 30 to 50% of adults in any given year. People experiencing neck pain commonly report difficulties in performing activities involving the upper extremity. Furthermore, clinical trials that have included exercises that target the shoulder girdle have shown beneficial effects in reducing neck pain. These observations are feasible based on the biomechanical dependence of the cervical spine and shoulder girdle, which includes common muscle attachments. However, to date there has been a paucity of studies investigating underlying movement disorders of the shoulder girdle in people with neck pain. This is in part due to the challenges of kinematic measurement in this region. The aim of this thesis is to contribute to the literature concerning the role of the shoulder girdle and thorax complex in neck pain from three perspectives. First, the thesis has further refined and informed measurement methods of shoulder girdle and thoracic kinematics (Studies 1-3). Secondly, the thesis further defined normative kinematics of the region with a focus on upright resting posture (Study 4). Thirdly, the thesis explored differences in shoulder girdle and thoracic resting posture in upright standing in those with and without neck pain (Study 5).Advancement in knowledge concerning normal and impaired function of the shoulder girdle has been hindered by challenges related to 3D motion capture of the shoulder girdle and thorax due to skin movement and the complexity of measuring multiple joints and axes of rotation. Therefore, Study1 focused on refining and validating an acromion marker cluster (AMC) method to track scapular movement with the intent of minimising skin movement error. Although the findings of Study 1 indicated that the refined AMC design did not appear to lessen skin movement error compared to previous designs, it was found to be of comparable accuracy (max RMSE 4.45°) and reliability to previous designs (within- ession test-retest ICC 0.79-0.99) and appropriate for use in the subsequent thesis studies. In Study 2 the reliability and validity of the AMC method was further evaluated in its capacity to track the scapula at end range clavicular movements (protraction/retraction, elevation/depression). Establishing its measurement accuracy and reliability (max RMSE 6.6°) in these common directions of scapula motion was necessary as it had been previously unstudied. While Studies 1 and 2 focused on optimising the measurement of scapulothoracic kinematics by ensuring the scapula could be tracked accurately, Study 3 focused on refining the measurement of the relationship between the shoulder girdle and the underlying thorax. This study compared thoracic and shoulder girdle postural relationships expressed in the external reference frame to that expressed in the traditionally used ISB recommended thorax reference frame. Using these different frames of reference Study 3 also compared measures of thoracic inclination and thoracic curvature. The findings showed that measurements of thoracic inclination expressed in the external reference frame provided additional insight into scapulothoracic relationship compared to traditional measurements in the thorax reference frame. Study 4 then utilized the refined measurements of the scapula and thorax to more accurately describe normative shoulder girdle parameters, and to identify individual characteristics underpinning variations in these parameters, in a large cohort of asymptomatic individuals. This study demonstrated that scapular resting posture is strongly associated with thoracic inclination (scapular anterior/posterior tilt) and clavicular posture (scapular internal and upward rotation). Based on the results of Study 4, shoulder girdle resting posture and thoracic spine parameters were compared in individuals with (n=53) and without (n=100) chronic neck pain. The results presented in Study 5 show that mild differences in shoulder girdle and thoracic posture may exist between people with and without chronic non-specific neck pain. In summary, this thesis explores and improves upon the current methodology of investigating relationships between the thorax and shoulder girdle. It further defines normative characteristics of shoulder girdle kinematics and thus enabled comparison to a neck pain population. Understanding these relationships and the association between shoulder girdle function and neck pain will facilitate future development of patient-centred management approaches for those suffering with neck pain.