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 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
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.
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.
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.
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.
Biceps brachii
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.
In 10% of cases, a third head arises from the superomedial part of brachialis and is attached to the bicipital aponeurosis and medial side of the tendon of insertion. It usually lies behind the brachial artery, but it may consist of two slips, which descend in front of and behind the artery. Less often, other slips may spring from the lateral aspect of the humerus or intertubercular sulcus.
Biceps is overlapped proximally by pectoralis major and deltoid; distally it is covered only by fasciae and skin, and it forms a conspicuous elevation on the front of the arm. Its long head passes through the shoulder joint; its short head is anterior to the joint. Distally it lies anterior to brachialis, the musculocutaneous nerve and supinator. Its medial border touches coracobrachialis, and overlaps the brachial vessels and median nerve; its lateral border is related to deltoid and brachioradialis.
Biceps brachii is typically supplied by up to eight vessels originating from the brachial artery in the middle third of the arm. These vessels pass laterally, posterior to the median nerve and divide into ascending and descending branches just before reaching the deep surface of the muscle. Smaller branches arise from the anterior circumflex humeral artery and the deltoid branch of the acromial division of the thoracoacromial axis.
There is great variation in the arterial supply to the muscle. The main arterial supply may originate from the superior or inferior ulnar collateral artery, subscapular artery, axillary artery, ulnar or radial arteries in cases of proximal bifurcation of the brachial artery, or the profunda brachii artery.
Biceps brachii is innervated by the musculocutaneous nerve, C5 and 6, with separate branches passing to each belly.
Biceps brachii is a powerful supinator, especially in rapid or resisted movements. It flexes the elbow, most effectively with the forearm supinated, and acts to a slight extent as a flexor of the shoulder joint. It is attached, via the bicipital aponeurosis, to the posterior border of the ulna, the distal end of which is drawn medially in supination. The long head helps to check upward translation of the humeral head during contraction of deltoid. When the elbow is flexed against resistance, the tendon of insertion and bicipital aponeurosis become conspicuous.
Lowering the hand under the influence of gravity by extension at the elbow calls for controlled lengthening of biceps. This is an example of a habitual movement in which muscle tension increases despite increasing length. As the hand descends and the elbow extends, the vertical through the centre of gravity of the forearm is carried further from the fulcrum of movement; the turning moment exerted by the load therefore increases and must be matched by an increase in the moment exerted by the muscle.
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