Shoulder (Glenohumeral) Joint
The shoulder joint (glenohumeral joint) is the most flexible joint in the human body. Due to its numerous ligaments and muscles, it is also a quite strong and physically powerful ball-and-socket joint (spheroidal joint).
The structure of the joint consists of the head of the humerus that fits inside a socked called the glenoid cavity. In turn, the entire formation is enclosed within an articular capsule that is reinforced by ligaments. Any sliding or slipping of the joint is prevented by the rotator cuff muscles that fix it in place and allow several actions to be carried out. More details about everything relating to the shoulder joint can be found in this article.
Anatomy & Structure of the shoulder joint
Bones and Ligaments
The shoulder joint consists of:
- The humeral head.
- The socket (glenoid cavity). The socket is part of the shoulder blade (scapula) and is enlarged by the glenoid labrum, a “lip” of fibrocartilage.
- The articular capsule which completely surrounds the cavity and is reinforced by several ligaments (coracohumeral ligament, glenohumeral ligaments).
Muscles & Function
The muscle system is significantly important for the stability and movements of the shoulder joint, especially the rotator cuff. The rotator cuff consists of the following four muscles: subscapularis muscle, teres minor muscle, infraspinatus muscle and supraspinatus muscle. The functions of this muscle group are various. On the one hand they fix the humeral head to the socket; on the other hand, they execute different movements. They allow both the internal and external rotation of the humeral head and furthermore the abduction, adduction, and retroversion.
The long tendon of the two-headed Biceps brachii muscle originates at the supraglenoid tubercle and passes through the rotator cuff. The origin of the short tendon of the biceps is the coracoid process (“raven's beak” extension). The insertion of the biceps is the radial tuberosity and the antebrachial fascia of the forearm. The contraction of the biceps brachii muscle leads to an abduction, adduction or anteversion, depending on the particular contracting part.
The acromion (highest point of the shoulder) is a bony part of the scapula. Together with the coracoid process, it forms a cavity in which the humeral head and the tendon of the supraspinatus muscle moves. This cavity comprises an important synovial bursa (subacromial bursa) which provides a buffer reducing compression and friction forces. However the bursa may also cause problems, e.g. it can become inflamed through overuse or injury.
- The shoulder (glenohumeral) joint is a synovial, ball-and-socket joint.
- It is the result of articulation between the head of the humerus and the glenoid cavity of the scapula.
- It is stabilized by a group of muscles called the rotator cuff.
- It allows a wide range of movement (flexion, extension, abduction, adduction, and circumduction)
- The subacromial bursa reduces compression on the shoulder joint.