CHAPTER 47 Upper arm

SKIN AND SOFT TISSUE

SKIN

Cutaneous vascular supply

The blood supply to the skin of the upper arm can be divided into three regions with separate supply: the deltoid region, supplied by musculocutaneous perforators, and the medial and lateral regions, supplied by fasciocutaneous perforators (Cormack & Lamberty 1994; Salmon 1994) (Fig. 47.1, Fig. 47.2).

Fig. 47.1 Transverse section through the upper arm to show the location of fasciocutaneous perforators lying on the superficial aspect of the deep fascia.

Fig. 47.2 Muscles of the left upper arm, viewed from the lateral aspect showing fasciocutaneous and musculocutaneous perforating vessels.

The deltoid region is supplied by the posterior circumflex humeral artery (p. 817) via musculocutaneous perforators. After the posterior circumflex humeral artery passes through the quadrangular space (p. 814) it gives off a descending branch, which runs down to the deltoid insertion and the overlying skin, and an ascending branch which passes superiorly towards the acromion, pierces the edge of deltoid and the deep fascia to fan out and supply the overlying skin.

The medial side of the upper arm is supplied by five or six fasciocutaneous perforators which arise from the brachial artery, the superior ulnar collateral artery and, if present, the single artery to biceps. These perforators pass along the medial intermuscular septum to spread out in the deep fascia and anastomose with perforating vessels superiorly and inferiorly and from the lateral side. There are virtually no musculocutaneous perforators through biceps or triceps.

The lateral side of the upper arm below deltoid is supplied by perforating vessels from the middle collateral and radial collateral arteries (the terminating bifurcation of the profunda brachii). The middle collateral artery sends perforators to the skin via the lateral intermuscular septum between brachioradialis and triceps, while the radial collateral artery gives off cutaneous perforators via the intermuscular septum between brachialis and brachioradialis. These cutaneous vessels anastomose with those from the medial side.

Cutaneous innervation

The skin of the shoulder region is supplied by the supraclavicular nerves from the cervical plexus. The floor of the axilla and upper medial surface of the arm is supplied by the lateral branch of the second intercostal nerve (the intercostobrachial nerve). The lower aspect of the medial side of the upper arm is supplied by the medial cutaneous nerve of the arm. The lateral aspect of the upper arm is supplied by the upper lateral cutaneous nerve (a branch of the axillary nerve) and the lower lateral cutaneous nerve (a branch of the radial nerve). The posterior aspect is supplied by the posterior cutaneous nerve of the arm, a branch of the radial nerve (Fig. 45.15, Fig. 45.14).

SOFT TISSUE

Brachial fascia

Brachial fascia, the deep fascia of the upper arm, is continuous with the fascia covering deltoid and pectoralis major: it forms a thin, loose sheath for muscles of the upper arm, and sends septa between them. It is thin over biceps, but thicker over triceps and the humeral epicondyles, and is strengthened by fibrous aponeuroses from pectoralis major and latissimus dorsi medially and from deltoid laterally. Strong medial and lateral intermuscular septa extend from it on each side.

The lateral intermuscular septum extends distally from the lateral lip of the intertubercular sulcus of the humerus along the lateral supracondylar ridge to the lateral epicondyle, and blends with the tendon of deltoid. It gives attachment to triceps behind, and brachialis, brachioradialis and extensor carpi radialis longus in front. It is perforated in the middle third by the radial nerve and the radial collateral branch of the profunda brachii artery. The thicker medial intermuscular septum extends from the medial lip of the intertubercular sulcus, distal to teres major, along the medial supracondylar ridge to the medial epicondyle, and blends with the tendon of coracobrachialis. It gives attachment to triceps behind, and brachialis in front. It is perforated by the ulnar nerve, superior ulnar collateral artery, and the posterior branch of the inferior ulnar collateral artery. At the elbow, the brachial fascia is attached to the epicondyles of the humerus and the olecranon of the ulna, and is continuous with the antebrachial fascia. Medially, just below the middle of the upper arm, it is traversed by the basilic vein and lymphatic vessels and, at various levels, branches of the brachial cutaneous nerves.

Together, the lateral and medial intermuscular septa of the upper arm divide the upper arm into anterior and posterior compartments.

MUSCLES

The muscles of the upper arm are coracobrachialis, which acts only on the shoulder joint; biceps and triceps, which cross both shoulder and elbow joints; and brachialis, which acts only at the elbow joint (Fig. 47.2, Fig. 47.3).

Fig. 47.3 Muscles, vessels and nerves of the left upper arm, viewed from the posterior aspect.

(From Sobotta 2006.)

ANTERIOR COMPARTMENT

Coracobrachialis

Attachments

Coracobrachialis arises from the apex of the coracoid process, together with the tendon of the short head of biceps, and also by muscular fibres from the proximal 10 cm of this tendon; it ends on an impression, 3–5 cm in length, midway along the medial border of the humeral shaft between the attachments of triceps and brachialis (Fig. 46.20, Fig. 47.4). Accessory slips may be attached to the lesser tubercle, medial epicondyle or medial intermuscular septum.

Fig. 47.4 A, Transverse section through the left arm a little below the middle of the shaft of the humerus. B, MRI scan at similar level.

Relations

Coracobrachialis forms an inconspicuous rounded ridge on the upper medial side of the arm; pulsation of the brachial artery can be felt and often seen in the depression behind it. The muscle is perforated by the musculocutaneous nerve. Anteriorly it is related to pectoralis major above and, at its humeral insertion, to the brachial vessels and median nerve, which cross it. The tendons of subscapularis, latissimus dorsi, and teres major, the medial head of triceps, the humerus and the anterior circumflex humeral vessels all lie posterior. The axillary artery (third part) and proximal parts of the median and musculocutaneous nerves lie medial. Biceps and brachialis lie lateral.

Vascular supply

One or more branches from the axillary artery pass deep to the lateral root of the median nerve, and the musculocutaneous nerve, to reach the deep surface of the muscle. Branches from the anterior circumflex humeral artery also supply the deep surface of the muscle. The accompanying artery of the musculocutaneous nerve sends a recurrent branch to the coracoid attachment and gives off a series of branches to the muscle during its intramuscular course. Accessory branches from the thoracoacromial artery provide additional supply to the superficial part of coracobrachialis.

Innervation

Coracobrachialis is innervated by the musculocutaneous nerve, C5, 6 and 7.

Actions

Coracobrachialis flexes the arm forward and medially, especially from a position of brachial extension. In abduction it acts with anterior fibres of deltoid to resist departure from the plane of motion.

Clinical anatomy: testing

Coracobrachialis can be tested by palpating its fibres during shoulder flexion against resistance.

Biceps brachii

Attachments

Biceps brachii derives its name from its two proximally attached parts or ‘heads’ (Fig. 46.20). The short head arises by a thick flattened tendon from the coracoid apex, together with coracobrachialis. The long head starts within the capsule of the shoulder joint as a long narrow tendon, running from the supraglenoid tubercle of the scapula at the apex of the glenoidal cavity, where it is continuous with the glenoidal labrum (p. 805). The tendon of the long head, enclosed in a double tubular sheath (an extension of the synovial membrane of the joint capsule), arches over the humeral head, emerges from the joint behind the transverse humeral ligament, and descends in the intertubercular sulcus, where it is retained by the transverse humeral ligament and a fibrous expansion from the tendon of pectoralis major. The two tendons lead into elongated bellies that, although closely applied, can be separated to within 7 cm or so of the elbow joint. At this joint they end in a flattened tendon, which is attached to the rough posterior area of the radial tuberosity; a bursa separates the tendon from the smooth anterior area of the tuberosity. As it approaches the radius, the tendon spirals, its anterior surface becoming lateral before being applied to the tuberosity. The tendon has a broad medial expansion, the bicipital aponeurosis, which descends medially across the brachial artery to fuse with deep fascia over the origins of the flexor muscles of the forearm (Fig. 47.5). The tendon can be split without difficulty as far as the tuberosity, whence it can be confirmed that its anterior and posterior layers receive fibres from the short and long heads, respectively.