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Background Immobilization in external rotation after a first-time shoulder dislocation was introduced to reduce the risk of recurrence compared to immobilization in internal rotation, but its efficacy remains controversial. The purpose of this study was to determine the long-term effect of immobilization in external rotation after a first-time shoulder dislocation. Methods Between October 2000 and March 2004, 198 patients with a first-time anterior dislocation of the shoulder (average age 28) were randomly assigned to immobilization in external rotation (ER group = 104 shoulders) or internal rotation (IR group = 94 shoulders) for 3 weeks. At an average 2-year follow-up, 159 patients (80.3%) were available for evaluation. In the current study, these 159 patients were further followed up and interviewed by telephone. The following items were evaluated: recurrent instability, apprehensive feeling, surgical intervention, limitation in the range of motion, return to sports, and the single assessment numeric evaluation (SANE) score. Results The average follow-up period was 18.2 years (range, 16 – 20 years). Fifty-six patients were available for follow-up with the follow-up rate of 35%. The recurrent patients were 6/27 (22%) in the ER group and 6/29 (21%) in the IR group (p = 0.889). The surgically stabilized patients were 3/27 (11%) in the ER group and 10/29 (34%) in the IR group (p = 0.038). In total, the recurrence rate was 9/27 (33%) in the ER group and 16/29 (55%) in the IR group (p = 0.100). Adding the surgical cases and those with the SANE score ≤ 70% as failure cases, the failure rate was significantly lower in the ER group (26%) than in the IR group (52%) (p = 0.048). Among those who survived without surgical intervention, there were no significant differences in apprehensive feeling, return to sports, limited range of motion, and the SANE score between the groups. Conclusions Immobilization in external rotation reduced the risk of surgical intervention compared to internal rotation in the long-term.

Scapulohumeral rhythm (SHR) provides insight to neuromuscular control and fundamental biomechanics of the shoulder. This rhythm often is disrupted in pathologic shoulders. As the first step, we sought to quantify SHR in healthy subjects for diagnostic assessment of shoulder function. Ten healthy shoulders were studied. Three-dimensional models of the humerus and scapula were created from computed tomography scans. Dynamic shoulder motion was recorded by use of single-plane fluoroscopy during arm abduction with 0-kg and 3-kg handheld loads. Shoulder kinematics were quantified by use of model-based 3-dimensional-to-2-dimensional registration techniques. SHR decreased (more scapular motion) with increasing abduction. With a 3-kg load, scapulothoracic motion was significantly reduced through the range of 35 degrees to 45 degrees of glenohumeral motion. Muscular stabilization of the scapula increased with external loading, as shown by decreased SHR during early lifting. Dynamic scapular stabilization provides a critical platform for upper extremity activity.

The purpose of this study was to investigate glenohumeral translation in-vivo during active shoulder abduction in the scapular plane. Three-dimensional (3D) models of 9 shoulders were created from CT scans. Fluoroscopic views aligned to the plane of the scapula were recorded during active arm abduction with neutral rotation. 3D motions were determined using model-based 3D-to-two-dimensional (2D) registration. Humeral translation was referenced to the glenoid center in the superior/inferior direction. The humerus moved an average of 1.7 mm superior with arm abduction, from an inferior location to the glenoid center. The humeral head was centered within 1 mm from the glenoid center above 80 degrees abduction. Variability in glenohumeral translation between shoulders decreased significantly from initial to final arm abduction. Our findings agree with some authors' observations of inferior-to-central translation of the humerus and behavior as a congruent ball and socket. We believe this information will help improve the understanding of shoulder function.