Shoulder kinematics in patients with full-thickness rotator cuff tears after a subacromial injection

The purpose of this study was to test the hypothesis that scapulohumeral rhythm (SHR) is altered in patients with full-thickness rotator cuff tears due to pain. Fifteen subjects (mean age, 60.2 ± 8.9 years; mean height, 1.72 ± 0.10 m; mean weight, 85.43 ± 18.32 kg) performed humeral elevation in the 3 planes before and after a lidocaine injection. Pain was assessed by use of a visual analog scale, and data were collected with an electromagnetic tracking system. Three-dimensional scapular kinematics (scapulothoracic motion) and glenohumeral elevation were assessed. A linear regression model was used to calculate SHR (ratio of scapulothoracic motion to glenohumeral elevation) for equal phases of elevation (I, II, and III) and lowering (IV, V, and VI). Pain was significantly reduced (P ≤ .05), causing shifts in SHR to occur for frontal plane elevation (phase III, 1:1.72 to 1:2.78; phase V, 1:1.56 to 1:2.56), resulting in an increase in glenohumeral motion and a reduced reliance on scapular rotation for humeral motion. As SHR decreased, the contribution of glenohumeral elevation increased significantly whereas scapular upward and downward rotation tended to decrease. Differences in anterior-posterior and medial-lateral tilting of the scapula did not correspond with changes in SHR. The findings provide evidence of compensatory increases in SHR due to pain associated with full-thickness rotator cuff tear.