This is a functional anatomy review of the shoulder complex. It covers the scapulothoracic mechanism, the sternoclavicular and acromioclavicular joints, and glenohumeral stability. It closes by integrating these into a model of coordinated upper extremity elevation.
Think of the glenohumeral joint as a golf ball on a tee. The glenoid covers only a quarter to a third of the humeral head, so stability is a soft tissue job, not a bony one. That framing drives every instability workup. When you see recurrent anterior dislocation, the failure is usually the labrum and the anterior band of the inferior glenohumeral ligament, the primary restraint above 90°.
The rotator cuff force couple is the other half of the story. The cuff depresses and compresses the head so the deltoid can abduct without driving the tubercle into the acromion. A torn cuff loses that counterforce, which is why the head migrates superiorly and the acromiohumeral distance narrows below the normal 9-10 mm.
Finally, scapulohumeral rhythm matters clinically because dyskinesis or a stiff kyphotic thorax changes the base the humeral head moves on, contributing to impingement.
This is a functional anatomy review of the shoulder complex. It covers the scapulothoracic mechanism, the sternoclavicular and acromioclavicular joints, and glenohumeral stability. It closes by integrating these into a model of coordinated upper extremity elevation.
Think of the glenohumeral joint as a golf ball on a tee. The glenoid covers only a quarter to a third of the humeral head, so stability is a soft tissue job, not a bony one. That framing drives every instability workup. When you see recurrent anterior dislocation, the failure is usually the labrum and the anterior band of the inferior glenohumeral ligament, the primary restraint above 90°.
The rotator cuff force couple is the other half of the story. The cuff depresses and compresses the head so the deltoid can abduct without driving the tubercle into the acromion. A torn cuff loses that counterforce, which is why the head migrates superiorly and the acromiohumeral distance narrows below the normal 9-10 mm.
Finally, scapulohumeral rhythm matters clinically because dyskinesis or a stiff kyphotic thorax changes the base the humeral head moves on, contributing to impingement.