Axillary area

On the upper limb, including its girdle (shoulder) and the free part of the upper limb, a number of bone and muscle landmarks are easily identified. These are the spine of the scapula, the acromial process, the medial and lateral borders, and the inferior angle of the scapula. In the subclavian region, the clavicle and the coracoid process of the scapula are visible. The deltoid region, delimited in front from the pectoralis major muscle by the deltoid-pectoral groove, is occupied by the massive deltoid muscle. The axillary region corresponds to the axillary fossa, which is clearly visible when the arm is abducted, the anterior border of which is determined by the lower edge of the pectoralis major muscle, and the posterior border by the lower edge of the latissimus dorsi muscle. On the shoulder, the medial and lateral grooves are visible, passing distally into the cubital fossa and delimiting the anterior group of shoulder muscles from the posterior. Near the elbow bend, the medial and lateral epicondyles of the humerus are easily palpated, and the olecranon process protrudes on the dorsal side of the elbow joint. On the anterior surface of the forearm, the radial and ulnar grooves, as well as the flexor tendons of the wrist and hand, are weakly outlined. Slightly proximal to the flexion-extension line of the wrist joint, the styloid process of the radius and ulna can be felt. On the palm, the elevations of the thumb and little finger are visible, and between them is a triangular palmar cavity, the base of which is turned towards the fingers. The joint lines between the phalanges and fingertips are well marked. The dorsal surface of the hand is convex. At the base of the thumb, when it is abducted, a pit is visible between the tendons of the long and short extensors of the thumb, which is called the anatomical snuffbox. Here, deep down, under the fascia, the radial artery passes in an oblique direction, heading towards the palm through the first interdigital space.

The skin in the scapular region is thick, tightly fused with the subcutaneous tissue and the superficial fascia by numerous fibrous fibers. The skin above the deltoid muscle is also thick and slightly mobile. In the subclavian region, the skin is thin, the subcutaneous tissue is well developed here, especially in women.

The axillary region is exposed when the upper limb is abducted. It has the shape of an axillary fossa, limited by the lower edge of the pectoralis major muscle (in front) and the latissimus dorsi muscle (in back). The medial border runs along the line connecting the lower edges of these muscles, which corresponds to the 3rd rib. Laterally, the border is on the medial surface of the shoulder along the line connecting the edges of the muscles attached to the humerus mentioned above. The skin of the axillary fossa, starting from the period of puberty, has a hairy covering. There are many sweat and sebaceous glands in the skin. The subcutaneous tissue is poorly expressed. In the shoulder area, the skin has different thicknesses. In the lateral and posterior parts it is thicker than in the medial part, the subcutaneous tissue is loose. Thick skin is present on the posterior surface of the elbow joint, and thin on its anterior surface. Above the tip of the olecranon there is an olecranon subcutaneous synovial bursa, which in case of trauma or prolonged pressure can be the "object" of the disease (bursitis). In the area of the anterior surface of the forearm the skin is thin and mobile, on the back it is thicker, its mobility is less. On the palm of the hand the skin is thick, slightly mobile, devoid of hair, the subcutaneous tissue has a cellular structure. On the back of the hand the skin is thin, mobile, in places of hair roots there are sebaceous glands. The subcutaneous tissue is loose, which contributes to the formation of edema here in inflammatory diseases of the hand.

After dissection of the axillary fascia, the axillary cavity (cavum axillare) is opened, which has the shape of a four-sided pyramid, the apex of which is directed upward and medially, and the base is directed downward and laterally. The upper aperture of the axillary cavity, limited by the clavicle (in front), the 1st rib (medially) and the upper edge of the scapula (behind), connects the axillary cavity with the neck region. The axillary cavity has 4 walls. The anterior wall is formed by the pectoralis major and minor muscles covered with fascia; the posterior wall is formed by the latissimus dorsi, teres major and subscapularis muscles. The medial wall is represented by the serratus anterior muscle, the lateral wall is represented by the biceps brachii and coracobrachialis muscles.

In the area of the posterior wall of the axillary cavity, between the muscles there are two fairly large gaps (openings) covered with loose tissue.

The trilateral opening, located more medially, is bounded above by the lower border of the subscapularis muscle, below by the teres major muscle, and laterally by the long head of the triceps brachii. The artery and veins surrounding the scapula pass through the opening. The quadrilateral opening, located more laterally, is bounded by the surgical neck of the humerus (laterally), the long head of the triceps brachii (medially), the lower border of the subscapularis muscle (superiorly), and the teres major muscle (inferiorly). The posterior artery and veins surrounding the humerus and the axillary nerve pass through this opening. The axillary cavity contains loose fibrous connective tissue rich in fatty tissue that surrounds the vessels and nerves (axillary artery and vein, bundles of the brachial plexus and the beginning of the nerves extending from them), as well as the axillary lymph nodes.

On the anterior wall of the axillary fossa, 3 triangles are distinguished, within which the topography of the blood vessels and nerves located here is determined. These are the clavicular-pectoral, thoracic and infrapectoral triangles.

The clavipectoral triangle (trigonum clavipectorale), with its apex directed laterally, is limited at the top by the clavicle and at the bottom by the upper edge of the pectoralis minor muscle. Within its boundaries are the axillary artery and vein, and the medial bundle of the brachial plexus.

The thoracic triangle (trigonum pecrorale) corresponds to the pectoralis minor muscle. Here, the lateral thoracic artery branches off from the axillary artery and the long thoracic nerve passes.

The substernal triangle (trigonum subpectoral), which is located between the lower edges of the small and large pectoral muscles, contains the axillary artery and vein, as well as the median, musculocutaneous, ulnar and other nerves. In this same triangle, a number of large branches (the subscapular, anterior and posterior arteries that encircle the humerus) depart from the axillary artery.

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