Scapular Kinematics and Subacromial-Impingement Syndrome: A Meta-Analysis

Context: The literature does not present a consistent pattern of altered scapular kinematics in patients with shoulder-impingement syndrome (SIS). Objectives: To perform meta-analyses of published comparative studies to determine the consistent differences in scapular kinematics between subjects with SIS and controls. In addition, the purpose was to analyze factors of the data-collection methods to explain the inconsistencies in reported kinematics. The results of this study will help guide future research and enable our understanding of the relationship between scapular kinematics and SIS. Evidence Acquisition: A search identified 65 studies; 9 papers met inclusion criteria. Sample sizes, means, and SDs of 5 scapular-kinematic variables were extracted or obtained from each paper's lead author. Standard difference in the mean between SIS and controls was calculated. Moderator variables were plane of arm elevation, level of arm elevation (ARM) and population (POP). Evidence Synthesis: Overall, the SIS group had less scapular upward rotation (UR) and external rotation (ER) and greater clavicular elevation (ELE) and retraction (RET) but no differences in scapular posterior tilt (PT). In the frontal plane, SIS subjects showed greater PT and ER, and in the scapular plane, less UR and ER and greater ELE and RET. There was also greater ELE and RET in the sagittal plane. There was less UR at the low ARM and greater ELE and RET at the high ARM with SIS. Athletes and overhead workers showed less UR, while athletes showed greater PT and workers showed less PT and ER. The general population with SIS had greater ELE and RET only. Conclusions: Subjects with SIS demonstrated altered scapular kinematics, and these differences are influenced by the plane, ARM, and POP. Athletes and overhead workers have a different pattern of scapular kinematics than the general population. The scapular plane is most likely to demonstrate altered kinematics. These factors should be considered when designing futures studies to assess the impact of altered kinematics in patients with SIS.