Shoulder

Shoulder Joint: this joint hangs free from the axial skeleton and gets its mobility due to absence of bony constraints. The result is a very unstable joint. It is a ball-socket joint. But the glenoid socket contains only one-third of the humeral head. The humeral head is retroverted 30^o and medially inclined 45^o compared to long axis of the humerus. So, we have an upper limb well forward and away from body plane. The glenoid is slightly superiorly tilted and is thought to contribute to stability of the joint by preventing inferior subluxation of the humerus.

As the glenoid is rather shallow, we need additional supports to keep the joint together. The  role of glenoid labrum and gleno-humeral ligaments is discussed in the power point presentation. Glenoid labrum (GL) increases the depth of glenoid by 50%. Superiorly the long head of Biceps is attached and it can be disrupted here along with the GL in SLAP lesion. 

The gleno-humeral ligaments (GHL) are condensations of the joint capsule but provide good stability to the joint. Inferior GHL is the most important and is the primary anterior stabiliser of the abducted shoulder. 

Movement in the joint is mainly rotational, with little translation. It is helpful to remember that movement at the shoulder is not isolated but accompanied by movements at the scapulo-thoracic joints and the spine.

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