Scapular kinematics variability in individuals with and without rotator cuff-related shoulder pain: A systematic review with multilevel meta-regression

Background Traditionally, great importance has been placed on abnormal scapula kinematics in the approach to treatment of patients with rotator cuff related shoulder pain (RCRSP). Objective To review the literature regarding the variability of scapular position and movement in individuals with and without RCRSP. Methods A systematic search was performed on 18th April 2024 on nine databases. Studies evaluating scapular kinematics during arm elevation in healthy individuals and those with RCRSP were included, with a focus on 3D non-surface tracking systems. Results Twenty studies were included. In asymptomatic individuals, the estimated scapular position at rest was 1.00° to 11.58° of upward rotation (UR), 4.82° to 11.24° of anterior tilt, and 26.84° to 39.05° of internal rotation. During arm elevation, the scapula moves from the very beginning (no setting phase) towards UR (final position, 47.88° to 61.00° at 150° of elevation) and posterior tilt (final position, 10.78° to 11.96° at 150° of elevation), and there is a trend towards external rotation. The estimated scapulohumeral rhythm for humerothoracic elevation and scapular UR ranged from 2.86:1 to 3.13:1. There was very low certainty of evidence for differences in individuals with RCRSP in scapula resting position for UR (mean difference, -6.11°; 95 % CI: -7.36°, -4.86°), and internal rotation (mean difference, 4.21°; 95 % CI: 0.68°, 7.74°), that were below the width of the 95 % prediction intervals. Conclusion This meta-analysis has debunked the myth of the setting phase and the constant 3:1 scapulohumeral rhythm. There is great variability in scapular kinematics, making it difficult to detect abnormal patterns.