Anatomy of the shoulder joint

The shoulder joint is formed by the head of the humerus and the articular cavity of the scapula. The shoulder is formed and fixed at the expense of four muscles and their tendons: supraspinous, subacute, subscapular and round small muscle. The tendons of these muscles form a rotator cuff. The muscle is located above other muscles that form the rotator cuff. It begins in the vaginal fossa of the scapula, then passes under the acromial process and is attached to the anterior margin of the large tuberosity of the humerus. The function of this muscle is to withdraw the shoulder anteriorly and outward. The subacute muscle begins in the subacute of the scapula, passes more laterally and is also attached to the large tuberosity of the humerus, behind and below the supraspinatus.

The round small muscle starts from the lateral margin of the scapula and is attached to the large tuberosity of the humerus behind and down from the subaccessory muscle. Subacute and small round muscles rotate the shoulder outward. These three muscles, which form the rotator cuff, unite their fibers in a single tendon, which is then fixed to a large tuberosity.

The subscapularis muscle is the anterior of the four muscles. It starts from the medial part of the scapula, then crosses the anterior section of the scapula-humeral articulation and is attached to the small tuberosity of the humerus. An extremely important object in the study of the shoulder is the tendon of the long biceps head. This tendon starts from the upper-articular tubercle and the posterior-upper part of the joint lip. It passes in front of the head of the humerus between the supernumerary and subscapular muscles to enter the corresponding groove for the bicep tendon. The tendon of the biceps, thus, medially borders on a small tuberosity and laterally with a large tuberosity of the humerus. The synovial membrane of the biceps tendon is up to 3 cm in length from the groove of the biceps. The biceps tendon and the rotator cuff are separated from the deltoid muscle by a counterfeit-acromial bag.

Normally there is no communication between the counterfeit bag and the shoulder-and-shoulder joint. This bag is located anteriorly and above the tendon of the biceps, between the deltoid and subacute muscles.

The radial nerve is the largest branch of the brachial plexus. It is formed from various combinations of rootlets C5-T1 and innervates the motor bundles of the triceps, the brachial muscle, the brachial, the extensor carbide. The radial nerve provides sensitivity to the posterior surface of the skin in the distal 2/3 of the shoulder, the posterior surface of the forearm and the back surface of 1, 2, 3 fingers and, in part, 4 from the lateral side. The radial nerve emerges from the posterior part of the brachial plexus and follows along the triceps. Initially, it follows between the coracoid-brachial and circular muscles and further between the medial and lateral abdominals of the triceps. A deep brachial artery accompanies the radial nerve on its way. In the middle third of the shoulder, the nerve follows around the posterior surface of the humerus along the protruding line of the deltoid muscle. The nerve is fixed to the humerus, where it penetrates the muscular septum in the distal part of the shoulder, causing the most frequent nerve damage in fractures of the humerus below the middle and distal part.

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