Quantification of two-dimensional glenohumeral rhythm in persons with and without symptoms of shoulder impingement.

A repeated-measures design was used to assess glenohumeral rhythm in 10 patients with shoulder impingement and 10 pain-free persons and to assess the effects of subacromial injection on glenohumeral rhythm within the impingement group. Scapular-plane anterior-to-posterior x-rays of the scapula and humerus were obtained at 5 angles of arm elevation (resting, 30 degrees, 60 degrees, 90 degrees, 120 degrees). For the impingement group, x-rays were repeated after subacromial injection (10 mL of 1% lidocaine). No significant differences in glenohumeral rhythm were found between the impingement and control groups across all arm-elevation angles.