Shoulder joint

 ( Joints ) 

The tendon of the long head of the biceps brachii passes through the bicipital 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. Other long muscles such as pectoralis major, latissimus dorsi, teres major and Deltoid muscle also provide support to the shoulder joint.

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.

• Superior, middle and inferior glenohumeral ligaments. It is the thickenings of the capsule that passes from the upper part of glenoid to lesser tuberosity and inferior part of the head of humerus. These ligaments are weak unlike its posterior part which is supported by the infraspinatus muscle.
• Coracohumeral ligament
• Transverse humeral ligament
• Coraco-acromial ligament

The glenoid cavity is shallow and contains the glenoid labrum which deepens it and aids stability. With 120 degrees of unassisted flexion, the shoulder joint is the most mobile joint in the body.

The movement of the scapula across the rib cage in relation to the humerus is known as the scapulohumeral rhythm, and this helps to achieve a further range of movement. This range can be compromised by anything that changes the position of the scapula. This could be an imbalance in parts of the large that hold the scapula in place. Such an 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 in the (sagittal plane).
• Flexion is carried out by the anterior fibres of the deltoid, pectoralis major and the coracobrachialis.
• Extension is carried out by the latissimus dorsi and posterior fibres of the deltoid.
• Abduction and adduction of the shoulder (frontal plane).
• Abduction is carried out by the deltoid and the supraspinatus in the first 90 degrees. From 90-180 degrees it is the trapezius and the serratus anterior.
• Adduction is carried out by the pectoralis major, latissimus dorsi, teres major and the subscapularis.
• Horizontal abduction and horizontal adduction of the shoulder (transverse plane)
• Medial and lateral rotation of the shoulder (also known as internal and external rotation).
• Medial rotation is carried out by the anterior fibres of the deltoid, teres major, subscapularis, pectoralis major and the latissimus dorsi.
• Lateral rotation is carried out by the posterior fibres of the deltoid, infraspinatus and the teres minor.
• Circumduction of the shoulder (a combination of flexion/extension and abduction/adduction).

A SLAP tear (superior labrum anterior to posterior) is a rupture in the glenoid labrum. SLAP tears are characterized by shoulder pain in specific positions, pain associated with overhead activities such as tennis or overhand throwing sports, and weakness of the shoulder. This type of injury often requires surgical repair.

Anterior dislocation of the glenohumeral joint occurs when the humeral head is displaced in the anterior direction. Anterior shoulder dislocation often is a result of a blow to the shoulder while the arm is in an abducted position. In younger people, these dislocation events are most commonly associated with fractures on the humerus and/or glenoid and can lead to recurrent instability. In older people, recurrent instability is rare but people often suffer rotator cuff tears. It is not uncommon for the arteries and nerves (axillary nerve) in the axillary region to be damaged as a result of a shoulder dislocation; which if left untreated can result in weakness, muscle atrophy, or paralysis.

Subacromial bursitis is a painful condition caused by inflammation which often presents a set of symptoms known as subacromial impingement.

Arthrogram of shoulder joint (with or without computed tomography) is performed by injecting contrast below and lateral to the coracoid process to outline the shoulder joint. Axillary pouch of the shoulder can be seen on external rotation, while subscapular (subcoracoid) bursa can be seen on internal rotation of arm. The contrast should not enter subacromial bursa unless supraspinatus tendon is completely ruptured.