scapularis. The supra-acromial bursa does not normally communicate with the shoulder joint. Muscles 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 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 muscles also provide support to the shoulder joint. The tendons of the rotator cuff and their respective muscles (supraspinatus muscle, infraspinatus, teres minor, and subscapularis) stabilize and fix the joint. The supraspinatus, infraspinatus and teres minor muscles aid in abduction and external rotation. Ligaments Superior, middle and inferior glenohumeral ligaments. It is the thickenings of the capsule that pass 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 Innervation The nerves supplying the shoulder joint all arise in the brachial plexus. They are the suprascapular nerve, the axillary nerve and the lateral pectoral nerve. Blood supply The shoulder joint is supplied with blood by branches of the anterior and posterior circumflex humeral arteries, the suprascapular artery and the scapular circumflex artery. Function The rotator cuff muscles of the shoulder produce a high tensile force, and help to pull the head of the humerus into the glenoid cavity. 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 trapezius muscles that hold the scapula in place. Such an imbalance could cause a forward head carriage which in turn can affect the