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The right shoulder and Glenohumeral joint
The glenohumeral joint, (from ancient Greek glene, eyeball, puppet, doll + -oid, 'form of', + Latin humerus, shoulder) or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula (shoulder blade) and the head of the humerus (upper arm bone). Due to the very limited interface of the humerus and scapula, it is the most mobile joint of the human body.
The shoulder joint has a loose capsule that is lax inferiorly and therefore is at risk of dislocation inferiorly. The long head of the biceps brachii muscle travels inside the capsule to attach to the supraglenoid tubercle of the scapula.
Because the tendon is inside the capsule, it requires a synovial tendon sheath to minimize friction.
A number of bursae in the capsule aid mobility. Namely, they are the subdeltoid bursa (between the joint capsule and deltoid muscle), subcoracoid bursa (between joint capsule and coracoid process of scapula), coracobrachial bursa (between subscapularis muscle and tendon of coracobrachialis muscle), subacromial bursa (between joint capsule and acromion of scapula) and the subscapular bursa (between joint capsule and tendon of subscapularis muscle, also known as subtendinous bursa of subscapularis muscle). The bursa are formed by the synovial membrane of the joint capsule. An inferior pouching of the joint capsule between teres minor and subscapularis is known as the axillary recess.
The shoulder joint is a muscle dependent joint as it lacks strong ligaments. The primary stabilizers of the shoulder include the biceps brachii on the anterior side of the arm, and tendons of the rotator cuff; which are fused to all sides of the capsule except the inferior margin. The tendon of the long head of the biceps brachii passes through the intertubercular groove on the humerus and inserts on the superior margin of the glenoid cavity to press the head of the humerus against the glenoid cavity. The tendons of the rotator cuff and their respective muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) stabilize and fix the joint. The supraspinatus, infraspinatus and teres minor muscles aid in abduction and external rotation of the shoulder, while the subscapularis aids in internal rotation of the humerus.
- Superior, middle and inferior glenohumeral ligaments
- Coracohumeral ligament
- Transverse humeral ligament
- Coraco-acromial ligament
The glenohumeral joint is supplied with blood by branches of the anterior and posterior circumflex humeral, suprascapular arteries and the scapular circumflex arteries.
The glenoid fossa is shallow and contains the glenoid labrum which deepens it and aids in stability. With 120 degrees of unassisted flexion, the glenohumeral joint is the most mobile joint in the body.
Scapulohumeral rhythm helps to achieve further range of movement. The Scapulohumeral rhythm is the movement of the scapula across the thoracic cage in relation to the humerus. This movement can be compromised by anything that changes the position of the scapula. This could be an imbalance in the muscles that hold the scapula in place which are the upper and lower trapezius. This imbalance could cause a forward head carriage which in turn can affect the range of movements of the shoulder.
- Flexion and extension of the shoulder joint (sagittal plane). Flexion done by the Anterior Fibres of the Deltoid, Pectoralis Major and the Coracobrachialis. Extension is done by Latissimus Dorsi, Posterior Fibres of the Deltoid.
- Abduction and adduction of the shoulder (frontal plane). Abduction is done by Deltoid and the Supraspinatus in the first 90 degree. From 90-180 degree it is the Trapezius and the erratus Anterior. Adduction is done by Pectoralis Major, Lattisimus Dorsi, Teres Major and Subscapularis.
- Horizontal Abduction and Horizontal Adduction of the shoulder (transverse plane)
- Medial and lateral rotation of shoulder (also known as internal and external rotation). Medial Roatation is done by Anterior Fibres of Deltoid, Teres Major, Subscapularis, Pectoralis Major and the Lattissimus Dorsi. Lateral Rotation is done by Posterior Fibres of the Deltoid, Infraspinatus and the Teres Minor.
- Circumduction of the shoulder (a combination of flexion/extension and abduction/adduction)
The capsule can become inflamed and stiff, with abnormal bands of tissue (adhesions) growing between the joint surfaces, causing pain and restricting movement of the shoulder, a condition known as frozen shoulder or adhesive capsulitis.
- Saladin, Kenneth S. (2012). Anatomy & Physiology: The Unity of Form and Function (Sixth ed.). New York, NY: McGraw-Hill.
- Hub, Ken. The Rotator Cuff. 2014. 10 December 2014 <https://www.kenhub.com/en/library/anatomy/the-rotator-cuff>.
- Moore, K.; Dalley, A.; Agur, A. (2014). Moore Clinically Oriented Anatomy, (7th ed.). Lippincott Williams and Wilkins.
|Wikimedia Commons has media related to Glenohumeral joint.|
- Overview at brown.edu
- Overview at ouhsc.edu
- Anatomy figure: 10:03-12 at Human Anatomy Online, SUNY Downstate Medical Center
- Diagram at yess.uk.com