Chapter 6: Extremitas Superior: Upper Limb

The upper limb is built for mobility. It hangs from the trunk by a light, movable shoulder girdle and ends in a hand that can grip, pinch and manipulate. It has two parts:

• Cingulum membri superioris (shoulder girdle): the clavicle and scapula, which connect the limb to the trunk and anchor the muscles that move it.
• Pars libera (free limb): arm (brachium: humerus), forearm (antebrachium: radius and ulna), and hand (manus: carpals, metacarpals and phalanges).

Bones of the shoulder girdle

Clavicula

An S-shaped bone lying horizontally at the root of the neck. It is the only bony connection between the upper limb and the trunk.

• Extremitas sternalis: articulates with the manubrium (sternoclavicular joint).
• Extremitas acromialis: articulates with the acromion (acromioclavicular joint).
• Two surfaces (superior, smooth; inferior, rough), two borders (anterior, posterior).
• Sulcus musculi subclavii on the inferior surface, for the subclavius muscle.
• Tuberculum conoideum and linea trapezoidea on the inferior surface near the acromial end, for the two parts of the coracoclavicular ligament.

The clavicle is the most commonly fractured bone in the body, usually at the junction of its middle and lateral thirds, after a fall onto the outstretched hand.

Scapula

A flat, triangular bone on the posterior thoracic wall (over ribs II–VII).

• Two surfaces:
  • facies costalis (anterior): the fossa subscapularis;
  • facies posterior: divided by the spina scapulae into the fossa supraspinata (above) and fossa infraspinata (below). The spine ends laterally in the acromion.
• Three borders: superior (with the incisura scapulae, the suprascapular notch), medial (vertebral) and lateral (axillary).
• Three angles: superior, inferior, and lateral. The lateral angle carries the cavitas glenoidalis (glenoid cavity), with the tuberculum supraglenoidale above it (long head of biceps) and the tuberculum infraglenoidale below (long head of triceps).
• Processus coracoideus: a hook-like projection pointing forward above the glenoid. It anchors pectoralis minor, coracobrachialis and the short head of biceps.

Bones of the free limb

Proximal end:

• Caput humeri: the hemispherical head, facing medially into the glenoid.
• Collum anatomicum: the groove just around the head.
• Tuberculum majus (lateral) and tuberculum minus (anterior), with crests running down from each (crista tuberculi majoris and minoris).
• Sulcus intertubercularis: the groove between them, for the tendon of the long head of biceps.
• Collum chirurgicum (surgical neck): the narrow part below the tubercles, a common fracture site. The axillary nerve and posterior circumflex humeral artery wind around it.

Shaft:

• Tuberositas deltoidea: laterally, halfway down, for deltoid.
• Sulcus nervi radialis (radial or spiral groove): on the posterior surface, carrying the radial nerve and the deep brachial artery.

Distal end (the condylus humeri):

• Capitulum humeri: lateral, rounded, articulating with the radius.
• Trochlea humeri: medial, spool-shaped, articulating with the ulna.
• Epicondylus lateralis and epicondylus medialis: the extensor and flexor muscles of the forearm arise from them.
• Sulcus nervi ulnaris: behind the medial epicondyle. The ulnar nerve lies here; this is the "funny bone".
• Fossae: coronoid and radial in front, which receive the coronoid process and radial head in flexion; olecrani behind, which receives the olecranon in extension.

Ulna and radius

The ulna is on the medial (little finger) side and is the stable bone of the elbow:

• Olecranon: the point of the elbow.
• Processus coronoideus.
• Incisura trochlearis: the notch between olecranon and coronoid process, which grips the trochlea.
• Incisura radialis: for the radial head.
• Tuberositas ulnae: for brachialis.
• Caput ulnae (distally) and processus styloideus ulnae.

The radius is on the lateral (thumb) side and is the main bone of the wrist:

• Caput radii (a disc with a concave top, the fovea articularis), surrounded by the circumferentia articularis.
• Collum radii.
• Tuberositas radii: for biceps.
• The broad distal end, with the processus styloideus radii and the incisura ulnaris.

The two bones are joined along their length by the membrana interossea, a syndesmosis.

Manus: bones of the hand

• 8 ossa carpalia in two rows:

  • proximal row (lateral → medial): scaphoideum, lunatum, triquetrum, pisiforme;
  • distal row (lateral → medial): trapezium, trapezoideum, capitatum, hamatum.

  Mnemonic: "Some Lovers Try Positions That They Can't Handle". The two T's of the distal row go in order: trapezium sits by the thumb. The scaphoid is the most commonly fractured carpal bone; a fracture of its waist can cut off blood supply to the proximal fragment and cause avascular necrosis.

• 5 ossa metacarpalia (I–V), numbered from the thumb.

• 14 phalanges: the thumb (pollex) has two (proximal, distal); each other finger has three (proximal, middle, distal).

Joints and ligaments

The deck calls the shoulder joint "saddle in shape, ball in function", the same wording as for the sternoclavicular joint. By standard references the glenohumeral joint is a true ball-and-socket joint; only the sternoclavicular joint has the saddle-shaped surfaces.

A pulled elbow (subluxation of the radial head) happens in young children when the arm is yanked. The radial head slips out of the annular ligament.

Muscles

Back muscles that move the limb

The deck names the nerve to latissimus dorsi "n. thoracica". It is the thoracodorsal nerve (from the posterior cord).

Pectoral region

Shoulder (deltoid and scapular) region

The rotator cuff is four muscles whose tendons blend with the shoulder capsule and hold the humeral head in the glenoid: Supraspinatus, Infraspinatus, Teres minor, Subscapularis ("SITS"). Teres major is not part of it. The supraspinatus tendon, squeezed under the acromion, is the one most often torn or inflamed.

Arm (brachium)

The arm has two compartments separated by the humerus and intermuscular septa.

Anterior compartment (flexors), all supplied by the n. musculocutaneus:

Posterior compartment (extensor), supplied by the n. radialis:

Forearm (antebrachium)

Anterior compartment (flexors and pronators), arising mostly from the medial epicondyle (common flexor origin), in layers:

• Superficial layer: m. pronator teres, m. flexor carpi radialis, m. palmaris longus, m. flexor carpi ulnaris. (The deck also lists flexor digitorum superficialis here; many texts treat it as a middle layer.)
• Middle layer: m. flexor digitorum superficialis, which flexes the proximal interphalangeal joints.
• Deep layer:
  • m. flexor digitorum profundus, which flexes the distal interphalangeal joints;
  • m. flexor pollicis longus;
  • m. pronator quadratus.
• Nerve: the median nerve supplies all of them except flexor carpi ulnaris and the medial (ulnar) half of flexor digitorum profundus, which are supplied by the ulnar nerve. The deep layer is reached by the median nerve's anterior interosseous branch.

Posterior compartment (extensors and supinator), arising mostly from the lateral epicondyle (common extensor origin). All are supplied by the radial nerve or its deep branch (posterior interosseous nerve).

• Superficial layer:
  • m. brachioradialis, a flexor of the elbow despite being in this compartment;
  • m. extensor carpi radialis longus and brevis;
  • m. extensor digitorum;
  • m. extensor digiti minimi;
  • m. extensor carpi ulnaris;
  • m. anconeus.
• Deep layer:
  • m. supinator;
  • the three "thumb outcroppers", m. abductor pollicis longus, m. extensor pollicis brevis and m. extensor pollicis longus;
  • m. extensor indicis.

Hand (manus)

The hand's intrinsic muscles are supplied by the ulnar nerve, apart from the "LOAF" muscles, which get the median nerve: the first two Lumbricals, Opponens pollicis, Abductor pollicis brevis and Flexor pollicis brevis.

Topography

Fossa axillaris (the axilla)

A pyramid-shaped space between the arm and the chest wall.

Contents:

• the axillary artery and vein;
• the cords and branches of the brachial plexus;
• the axillary lymph nodes;
• the long thoracic nerve, on serratus anterior;
• lateral cutaneous branches of the intercostal nerves (intercostobrachial nerve);
• the cephalic vein, which reaches the axillary vein through the deltopectoral groove.

Spaces around the shoulder

Fossa cubiti (cubital fossa)

A triangular hollow in front of the elbow.

• Boundaries:

  • superior: an imaginary line between the two epicondyles;
  • medial: pronator teres;
  • lateral: brachioradialis.

• Floor: brachialis and supinator.

• Roof: deep fascia and the bicipital aponeurosis. In the roof (superficial fascia) run the cephalic, basilic and median cubital veins, which are used for venepuncture, and the medial and lateral cutaneous nerves of the forearm.

• Contents, from lateral to medial:

  • the radial nerve, deep under brachioradialis, dividing into its superficial and deep branches;
  • the biceps tendon;
  • the brachial artery, which divides here into radial and ulnar arteries;
  • the median nerve.

  Mnemonic: "TAN" (Tendon, Artery, Nerve) from lateral to medial. The bicipital aponeurosis protects the artery and nerve from a venepuncture needle.

Canalis carpi (carpal tunnel)

A tunnel at the wrist formed by the arch of carpal bones, roofed by the retinaculum musculorum flexorum (transverse carpal ligament).

• Attachments of the roof:
  • laterally, the scaphoid tubercle and trapezium;
  • medially, the pisiform and the hook of the hamate.
• Contents:
  • the four tendons of flexor digitorum superficialis;
  • the four tendons of flexor digitorum profundus;
  • the tendon of flexor pollicis longus;
  • the median nerve.

The ulnar nerve and artery pass outside the tunnel, superficial to the retinaculum (through Guyon's canal).

Anatomical snuffbox (fovea radialis)

The hollow on the back of the wrist at the base of the thumb, visible when the thumb is extended.

• Medial border: tendon of extensor pollicis longus.
• Lateral border: tendons of extensor pollicis brevis and abductor pollicis longus.
• Floor: scaphoid and trapezium.
• Proximal: styloid process of the radius.
• Contents: the radial artery. The superficial branch of the radial nerve and the start of the cephalic vein cross it superficially.

Tenderness in the snuffbox after a fall suggests a scaphoid fracture, even when the first radiograph looks normal.

Neurovasculature

Arteries

• The a. subclavia becomes the a. axillaris at the outer border of rib I.
• The axillary artery becomes the a. brachialis at the lower border of teres major. Its branches around the shoulder include the thoracoacromial artery, the lateral thoracic artery, the subscapular artery and the two circumflex humeral arteries.
• The brachial artery runs down the medial side of the arm, which is where a blood-pressure cuff compresses it. It gives off the a. profunda brachii (which runs with the radial nerve) and divides in the cubital fossa into:
  • the a. radialis, whose pulse is felt at the wrist lateral to the flexor carpi radialis tendon;
  • the a. ulnaris.
• In the hand they form the arcus palmaris superficialis (mainly from the ulnar artery) and the arcus palmaris profundus (mainly from the radial artery).

Veins

• Deep veins accompany the arteries and share their names (usually as pairs of venae comitantes).
• Superficial veins begin in the dorsal venous network of the hand:
  • the v. cephalica runs up the thumb (radial) side, through the deltopectoral groove, to the axillary vein;
  • the v. basilica runs up the little-finger (ulnar) side and pierces the deep fascia in the mid-arm to join the brachial veins, forming the axillary vein;
  • in the cubital fossa they are linked by the v. mediana cubiti, the usual vein for taking blood.

The brachial plexus

The whole upper limb is supplied by the plexus brachialis, formed by the ventral rami of C5–T1. It is organised in five stages:

1. Roots: C5, C6, C7, C8, T1.
2. Trunks:
   • superior (C5–C6);
   • middle (C7);
   • inferior (C8–T1).
3. Divisions: each trunk splits into an anterior and a posterior division (anterior for the flexor compartments, posterior for the extensor compartments).
4. Cords, named for their position around the axillary artery:
   • lateral (anterior divisions of the superior and middle trunks);
   • medial (anterior division of the inferior trunk);
   • posterior (all three posterior divisions).
5. Terminal branches (mnemonic for the stages: "Read That Damn Cadaver Book").

Two important branches arise from the roots rather than the cords:

• the n. dorsalis scapulae (C5), to the rhomboids;
• the n. thoracicus longus (C5–C7), to serratus anterior.

The n. suprascapularis comes from the superior trunk.

Lymphatic drainage

All lymph from the upper limb drains to the axillary lymph nodes, in five groups:

Superficial lymph from the ulnar side of the forearm and hand may first pass through the cubital (supratrochlear) nodes above the medial epicondyle. Because the anterior group drains most of the breast, the axillary nodes are examined, and often removed, in breast cancer.

Clinical correlations

Nerve injuries

Fracture of the humerus

The three nerves in contact with the humerus are each at risk at a typical fracture site:

• the axillary nerve at the surgical neck;
• the radial nerve in the radial groove (mid-shaft fracture), which is the one the deck emphasises. It can be stretched or torn, causing wrist drop;
• the ulnar nerve behind the medial epicondyle.

Epicondylitis

• Tennis elbow (lateral epicondylitis): pain over the lateral epicondyle, from overuse and degeneration of the common extensor origin (especially extensor carpi radialis brevis), for example from repeated backhand strokes. Pain is worse on resisted wrist extension.
• Golfer's elbow (medial epicondylitis): pain over the medial epicondyle, from overuse of the common flexor origin, for example from repeated gripping and swinging.

Key teaching point

Learn the upper limb as five nerves with territories:

Once the territories are known, each clinical picture (wrist drop, claw, benediction, winging) predicts itself.