The bony anatomy of the shoulder is one of minimal constraint. Therefore, glenohumeral ligaments play an important role in stabilizing the shoulder. The focus of many biomechanical investigations has been to clarify the function of glenohumeral ligaments at the extremes of shoulder motion “end range motion”. Atraumatic multidirectional instability is often associated with disability of glenohumeral ligaments, during mid range motion. However, it is impossible to know how they function in vivo during shoulder motion. To help elucidate this stabilizing role, we conducted in vivo three-dimensional kinematics of the normal shoulder joint using a three-dimensional image matching technique. Magnetic resonance images of 14 shoulder joints of 7 healthy volunteers were acquired for 7 isometric abduction positions between 0° and 180°. By combining in vivo three-dimensional kinematic data, with in vitro anatomical study of the ligaments, we simulated three-dimensional shortest paths between the origin and insertion of each ligament in each abduction position. At 0° of abduction, the posterior band of the coracohumeral ligament displayed a maximum length of 41.4mm ± 4.8. At 30° of abduction, the superior glenohumeral ligament displayed a maximum length of 38.0mm ± 5.2. At 60° of abduction, the anterior band of the coracohumeral ligament and the middle glenohumeral ligament displayed maximum lengths of, 39.3mm ± 5.0, 48.1mm ± 6.6 respectively. At 120° of abduction, the anterior band of the inferior glenohumeral ligament displayed a maximum length of 56.6mm ± 4.0. The present study had some limitations. The origin and insertion of the ligaments were determined only on the basis of the anatomical information of another subject. Although this measurement could not reflect the actual ligament length in each subject, we think that the maximum length of these results is an important influence on the function of the soft tissue stabilizer and could be essential when considering surgical procedures and physical exercise after surgery.
