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 18^th 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.