Shoulder Complex Kinematics in Individuals Clinically Classified with Multidirectional Instability: A Pre- Versus Post-Exercise Analysis

Abstract

Background: The clinical classification of glenohumeral joint instability is characterized by presumed increased humeral translations in conjunction with symptomology. Prior research reports inconsistent trends in glenohumeral joint kinematic differences between individuals clinically classified with glenohumeral joint instability and asymptomatic controls classified with stable shoulders. Limitations surrounding clinical classification criteria and motion tracking methods likely contribute to the lack of consistent kinematic trends. Additionally, the effect of participation in repetitive, resisted, shoulder activities in individuals clinically classified with glenohumeral joint instability has not yet been examined. Purpose and approach: The purpose of this dissertation was to implement previously validated methods to clinically classify individuals with presumed glenohumeral joint instability and utilize state-of-the art kinematic assessment methods to: (1) determine the glenohumeral joint kinematic characteristics of individuals clinically classified with instability, (2) investigate the glenohumeral and scapulothoracic joint kinematic effects of exposure to repetitive, resisted, shoulder activity in this group, and (3) explore the effect of scapulothoracic rotations on humeral translations during arm raising. Results: Results from aim 1 indicated individuals clinically classified with glenohumeral joint instability possessed significantly more average anterior humeral position (0.8 mm) compared to asymptomatic matched controls during unweighted scapular plane abduction (SAB). No other kinematic differences between groups were detected. Results from aim 2 identified there was a significant decrease in average normalized contact path length (10%) between the humeral head and glenoid face during SAB and significantly less average scapular internal rotation during SAB (2.5°) and humerothoracic internal rotation (IR) (3.2°) after exposure to moderate levels of repetitive, resisted, shoulder activity. Results from aim 3 indicated there was not a significant relationship between scapulothoracic rotation and humeral translations during SAB. Summary: Findings from aim 1 of this research demonstrated that only one out of four kinematic variables used measure glenohumeral joint stability were statistically different between individuals clinically classified with glenohumeral joint instability and matched controls during unweighted SAB. These findings suggest that the magnitude of joint stability classified with passive laxity tests may not necessarily relate to dynamic joint stability. Further, perhaps more consistent kinematic differences could be identified under more vigorous task conditions. Evidence from aim 2 of this research demonstrated that participation in moderate levels of shoulder activity provoked statistically different changes in only one out of four kinematic variables used to measure glenohumeral joint stability and resulted in minimal changes (≤3.2°) in scapulothoracic kinematics during active arm raising and a simulated swimming task. These findings suggest that perhaps participation in more strenuous repetitive, resisted, shoulder activities may induce greater kinematic effects. Lastly, findings from aim 3 do not suggest the magnitude of scapular rotations affect the amount of humeral translations in individuals clinically classified with glenohumeral joint instability and imply that other factors may potentially influence glenohumeral joint stability during activity.