Articulation & Type:
The shoulder joint is the joint of the upper limb that is formed by the articulation between the rounded head of the humerus and the shallow glenoid cavity of the scapula. The fibrocartilaginous ring makes the glenoid cavity deeper thus called the glenoid labrum or labrum glenoidale.
The articular surface of the humeral head is four times the area of the glenoid cavity.
The shoulder joint is also called the glenohumeral joint.
This joint is synovial ball and socket joint.
The capsule of the shoulder joint is thin and lax therefore it allows a wide range of movement.
This is attached to the epiphyseal line of the glenoid and the anatomical neck of the humerus, except inferiorly where it extends downwards on the medial aspect of the neck of the humerus as the axillary pouch.
The rotator cuff muscles around the shoulder joint provide strength to the capsule. These are as follows:
- Subscapularis muscle, anteriorly
- Supraspinatus muscle, superiorly
- Infraspinatus muscle, posteriorly
- Teres minor muscle, posteriorly
Hence these muscles plays an important role in stabilizing the shoulder joint
The synovial membrane lines the capsule of the shoulder joint.
The synovium extends along the tendon of the long head of biceps and beneath the tendon of subscapularis muscle forming subscapular bursa.
The long head of the biceps is, therefore, intracapsular but extrasynovial.
Ligaments Of Shoulder Joint:
The especially relevant ligaments of the shoulder joint are given below:
- Glenohumeral ligaments
- Transverse humeral ligament
- Coracohumeral ligament
The glenohumeral ligaments are the anterior thickenings of the capsule passing through the upper part of the glenoid to the lesser tuberosity of the humerus and the inferior part of the head of the humerus.
These ligaments strengthen the anterior part of the capsule.
The transverse humeral ligament bridges the gap between the greater and the lesser tuberosities of the humerus.
It maintains the long head of the biceps tendon within the bicipital groove.
The Coracohumeral ligament extends from the root of the coracoid process to the greater tuberosity of the humerus.
This ligament strengthens the capsule from above.
Stability Of Shoulder Joint:
In addition to ligaments, the surrounding muscles also stabilized the shoulder joint.
- The short muscles known as rotator cuff muscles. They are subscapularis, supraspinatus, infraspinatus and teres minor muscles.
- Furthermore, the long muscles that are long head of biceps, pectoralis major, latissimus dorsi, teres major and deltoid muscles.
The capsule is weakest at the inferior aspect of the shoulder joint and is least protected by muscles and ligaments; as a result, the inferior part of the shoulder joint is weakest.