Scapular Orientation During Planar and Three-dimensional Upper Limb Movements in Individuals with Anterior Glenohumeral Joint Instability

Abstract

The purpose of the study was to investigate whether individuals with anterior glenohumeral joint (GHJ) instability exhibit different scapular orientation from individuals with healthy shoulders in a planar shoulder movement and a functional three-dimensional (3D) reaching task. This is a between-groups study with repeated measures. Ten people with anterior GHJ instability and 15 people with healthy shoulders participated in the study. For the planar shoulder movement task, participants were asked to abduct the shoulder from the resting position to pre-determined target angles (45°, 90°, and 135° of shoulder abduction) in the frontal plane. For the 3D reaching task, participants were asked to move the unconstrained arm to a remembered target location in space. Scapular orientation about three rotational axes was analysed at the target location and compared between the two groups of subjects. For planar abduction, participants with GHJ instability and those with healthy shoulders exhibited similar scapular orientation changes in upward-downward rotation, anterior-posterior tipping and medial-lateral rotation. For 3D reaching, participants with GHJ instability and those with healthy shoulders also exhibited similar scapular orientation changes pointing to targets at various locations. Results of this study show that scapular orientation changes associated with shoulder abduction and functional reaching activities were similar in people with GHJ instability and those with healthy shoulders. The current study suggests that anterior GHJ instability has little impact on scapular kinematics during upper limb movements in a chronic condition without pain, muscle weakness or limited range of motion. Altered scapular kinematics may not contribute to the high recurrence rate of anterior GHJ dislocation.