Elbow and forearm

The primary function of the elbow is to help position the hand in space. This is achieved by means of three joints: the radiocapitellar, humero-ulnar and proximal radio-ulnar joints. The functional range of movement has been described by Morrey et al as being 30–130° of flexion, 50° of pronation and 50° of supination, but for modern living more flexion is required.

Core Procedures

Lateral, medial, anterior and posterior approaches to the elbow
Approaches to the radius and ulna

Surgical surface anatomy

The medial and lateral epicondyles of the distal humerus are palpable on the inner and outer aspects of the elbow, respectively. Posteriorly, the tip of the olecranon lies midway between the two epicondyles. The ulnar nerve is found at the midpoint of a line drawn between the olecranon and the medial epicondyle. Midway down the humerus, the ulnar nerve lies between the medial intermuscular septum and the medial head of triceps. From there, it passes into a sulcus behind the medial epicondyle and continues distally to pass between the two heads of flexor carpi ulnaris. It is commonly compressed behind the medial epicondyle, causing a cubital tunnel syndrome.

The bulk of the lateral aspect of the forearm is formed by a group of muscles known as the ‘mobile wad of Henry’. The ‘wad’ consists of brachioradialis, extensor carpi radialis longus and extensor carpi radialis brevis. The distal tendon of biceps brachii can be palpated in the antecubital fossa by performing O'Driscoll's hook test. An intact tendon will allow the examiner to hook an index finger under the intact biceps tendon from the lateral side.

Clinical anatomy

Bones and joints

The proximal side of the elbow joint is formed by the distal end of the humerus. This flares into the lateral epicondyle and capitulum laterally, and the medial epicondyle and trochlea medially. (For the avoidance of doubt, ‘capitulum’ is the term used by anatomists, whereas ‘capitellum’ and ‘capitellar’ are commonly used by surgeons: all terms refer to the same structure). Anterior and posterior fossae accommodate the coronoid and olecranon processes, respectively, at the extremes of range of elbow movement. The two ulnar processes join at the bare area to create the greater sigmoid notch of the elbow, with a lateral and medial facet separated by a central ridge. The proximal radius consists of a head and neck, and a medial bicipital tuberosity, around which the biceps tendon winds to become attached to its dorsal aspect. The proximal surface of the radius is a shallow concave fovea that articulates with the capitulum. On its medial side, the cylindrical head of the radius articulates with the radial notch of the ulna to form the proximal radio-ulnar joint ( Fig. 40.1 ).

The primary constraints of the elbow include the humero-ulnar joint, the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) complex.

The MCL consists of two functional parts that take origin from the anteroinferior portion of the medial humeral epicondyle. The anterior bundle is the strongest of all the elbow ligaments and inserts into the sublime tubercle on the medial surface of the coronoid. It resists valgus forces between 60° of flexion and full extension. The posterior bundle inserts into the medial surface of the olecranon.

The LCL complex has four components: the lateral ulnar collateral ligament (LUCL); anular ligament; radial collateral ligament (RCL) and accessory ligament. The RCL and LUCL take origin from the lateral epicondyle, where they blend with the muscular common extensor origin (CEO). The RCL and LUCL form a single broad band that inserts into the anular ligament and supinator crest. The LUCL is taut throughout the full range of elbow movement when a varus stress is applied. Injury to the LUCL results in a posterolateral rotatory instability (PLRI). The anular ligament is attached to the anterior and posterior margins of the radial notch of the proximal ulna and forms a sling around the radial head and neck, to which it has no attachment ( Fig. 40.2 ).

Fig. 40.2, The left elbow joint. A , Anterior aspect. B , Posterior aspect. C , Medial aspect. D , Lateral aspect.

Cubital fossa

The cubital fossa (antecubital fossa) forms part of the anterior aspect of the elbow and is in the shape of an inverted triangle. It is defined superiorly by an imaginary line joining the lateral and medial epicondyles, medially by the lateral border of pronator teres, and laterally by the medial border of brachioradialis. From superficial to deep, the roof of the triangle is formed by the skin, deep fascia of the forearm, cubital vein, medial cutaneous nerve of the forearm (a direct branch of the medial cord of the brachial plexus) and the bicipital aponeurosis. The deep contents, from medial to lateral, are the median nerve, the terminal branch of the brachial artery, the tendon of biceps brachii, the superficial branch of the radial nerve and the posterior interosseous nerve. Brachialis forms the floor of the triangle.

Muscles

The elbow is primarily flexed by brachialis, which is attached anterior to the coronoid process of the ulna. Biceps brachii also contributes to flexion but is primarily a supinator of the forearm ( ). It inserts as two distinct heads into the radial tuberosity: the long head proximally and the short head distally. These are ensheathed by the lacertus fibrosus, which wraps around the flexor–pronator mass. Biceps brachii is innervated by the musculocutaneous nerve. Posteriorly, triceps is the primary extensor of the elbow. It has three heads: the long and lateral heads are superficial and tendinous distally, while the deep medial head is muscular almost to the point of its insertion. It is innervated by the radial nerve.

Anterior compartment of the forearm

Superficial compartment

The muscles of the superficial group all arise from the medial epicondyle, or common flexor origin (CFO).

Pronator teres has two heads. The principal head arises from the medial epicondylar ridge, while a smaller (ulnar) head originates from the medial surface of the coronoid process. Together, they cross the forearm obliquely and insert into the lateral border of the radius at its point of maximum convexity. The principal action of pronator teres is to pronate the forearm but it is also a weak flexor of the elbow. Pronator teres is innervated by the median nerve, which passes between the two heads of the muscle; this is a site of potential entrapment.

Flexor carpi radialis (FCR) originates from the medial epicondyle of the humerus and inserts into the base of the second and third metacarpals. The radial artery and median nerve lie lateral and medial to it, respectively, in the forearm. FCR is a flexor and abductor of the wrist joint and is innervated by the median nerve.

Flexor digitorum superficialis (FDS) arises from the medial epicondyle of the humerus, the sublime tubercle of the ulna (ulnar head) and the entire length of the anterior oblique line of the radius (radial head). The muscle gives rise to four tendons, which pass deep to the flexor retinaculum (through the carpal tunnel) and insert into the bases of the middle phalanges of the index, middle, ring and little fingers. These flex the proximal interphalangeal joints of the fingers. FDS is innervated by the median nerve.

Palmaris longus is occasionally absent. When present, it originates at the common flexor origin and inserts into the palmar fascia as a long broad tendon that is closely related to the deeper median nerve. Palmaris longus is a weak flexor of the wrist. It is innervated by the median nerve.

Flexor carpi ulnaris (FCU) is the most dorsal tendon of the common flexor origin and has a broad secondary origin from the medial surface of the olecranon. At the leading edge is a fibrous band that connects the lateral epicondyle and olecranon (Osborne's ligament). It has a superficial fascia and a strong deep fascia (Osborne's fascia), which extends up to 9 cm from the medial epicondyle. Both can cause entrapment of the ulnar nerve. The tendon of FCU inserts into the pisiform and is a flexor and adductor of the wrist. FCU is innervated by the ulnar nerve.

Deep compartment

Flexor digitorum profundus (FDP) arises deep to the superficial tendons. It takes origin from the proximal three-quarters of the anterior and medial aspects of the ulna and the anterior ulnar half of the interosseous membrane. The muscle ends in four tendons in the forearm, which run through the flexor retinaculum and insert into the palmar surface of the bases of the distal phalanges. FDP is capable of flexing all the joints over which it passes but is the only muscle able to flex the distal interphalangeal joints. The medial part of FDP, i.e. the muscle bellies to the little and ring fingers, is innervated by the ulnar nerve. The lateral part, i.e. the muscle bellies to the middle and index fingers, is innervated by the anterior interosseous branch of the median nerve, C8 and T1.

Flexor pollicis longus (FPL) arises from the anterior surface of the radius distal to the anterior oblique line and inserts into the base of the distal phalanx of the thumb. It is the only flexor of the interphalangeal joint of the thumb and is innervated by the anterior interosseous nerve.

Pronator quadratus is a flat quadrangular muscle on the anterior aspect of the distal forearm. It arises from the distal quarter of the anteromedial shaft of the ulna and inserts into the distal quarter of the anterolateral shaft of the radius. It pronates the forearm and assists in maintaining stability of the distal radio-ulnar joint. Pronator quadratus is innervated by the anterior interosseous nerve.

Posterior compartment of the forearm

The common extensor origin (CEO) is an area on the anterior and lateral surfaces of the lateral epicondyle and is the origin of the common, or fused, tendon of extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi and extensor carpi ulnaris. At the wrist joint, the tendons are held in position by the extensor retinaculum, which is divided into six compartments ( Table 40.1 ). Anconeus originates on the posterior aspect of the lateral epicondyle of the humerus. The muscle is triangular in shape and diverges to insert into the lateral side of the ulna. Posteriorly, its fibres blend with triceps. It is a weak extensor and dynamic stabilizer of the elbow and is innervated by the radial nerve.

TABLE 40.1

The extensor compartments of the wrist from radial to ulnar

Compartment number	Contents
1	Abductor pollicis longus, extensor pollicis brevis
2	Extensor carpi radialis longus and brevis
3	Extensor pollicis longus
4	Extensor indicis, extensor digitorum
5	Extensor digiti minimi
6	Extensor carpi ulnaris

Brachioradialis arises from the upper two-thirds of the lateral epicondylar ridge. It becomes a flattened tendon as it reaches the midpoint of the forearm and subsequently inserts into the radial styloid. The radial nerve and artery are important relations of the posterior surface of the muscle and tendon. Brachioradialis is a flexor of the elbow and helps to bring the forearm into mid-pronation; it is innervated by the radial nerve.

Extensor carpi radialis longus (ECRL) arises deep to brachioradialis from the distal third of the lateral epicondylar ridge. It continues posterior to brachioradialis in the forearm before passing deep to the thumb muscles and inserting into the base of the second metacarpal. ECRL is an extensor and abductor of the wrist joint and is innervated by the radial nerve.

Supinator has two parts. The deep part originates from the supinator crest of the ulna and the superficial part from the lateral epicondyle, lateral collateral ligament and anular ligament. The muscle inserts into the neck and shaft of the radius. It is a supinator of the forearm, acting alone when the arm is in extension. Supinator is innervated by the posterior interosseous nerve, which passes between the two heads of the muscle; this is a site where compression may occur.

Extensor carpi radialis brevis (ECRB) arises from the CEO, travels down the forearm deep to ECRL and inserts into the base of the third metacarpal. ECRB is an extensor and abductor of the wrist and is innervated by the posterior interosseous nerve.

Extensor digitorum (extensor digitorum communis) arises from the CEO and the antebrachial fascia of the forearm. In the forearm, the muscle divides into four tendons, which insert into the extensor expansion of the middle and distal phalanges of the index, middle, ring and little fingers. The tendons to the ring and little finger are often fused, with only a small slip passing to the little finger distally in the hand. Extensor digitorum is innervated by the posterior interosseous nerve.

Extensor indicis (proprius) arises from the posterior surface of the ulna and the adjacent interosseous membrane, and runs distally to insert ulnar to the tendon of extensor digitorum. It assists in extending the index finger but because this function is also served by the index tendon of extensor digitorum, the proprius tendon can be used for tendon transfer. Extensor indicis is innervated by the posterior interosseous nerve.

Extensor digiti minimi arises as a small tendinous slip from the CEO, which inserts, through its tendon, into the extensor expansion of the little finger. It is often joined by the small slip from extensor digitorum. Extensor digiti minimi is innervated by the posterior interosseous nerve.

Extensor carpi ulnaris (ECU) is the final and most distal muscle arising from the CEO. Distally, it inserts into the base of the fifth metacarpal. ECU is an extensor and adductor of the wrist and can easily be palpated in the groove of the ulnar styloid if such movement is resisted. It is innervated by the posterior interosseous nerve.

Abductor pollicis longus (APL) arises from the proximal and posterior surface of the ulna, the adjoining interosseous membrane and the middle third of the posterior surface of the radius. It descends on the lateral aspect of the forearm, having crossed superficial to the extensors of the wrist, where a painful intersection syndrome may arise. It inserts into the base of the first metacarpal and extends and abducts the thumb at the CMC joint. APL is innervated by the posterior interosseous nerve.

Extensor pollicis brevis (EPB) arises from the posterior surface of the radius, distal to abductor pollicis longus, and from the adjoining interosseous membrane. It inserts into the base of the proximal phalanx of the thumb and extends the metacarpophalangeal joint. EPB is innervated by the posterior interosseous nerve.

Extensor pollicis longus (EPL) arises from the lateral, middle third and posterior surface of the ulna and the adjacent interosseous membrane. Having passed through the extensor retinaculum, it slings around Lister's tubercle to insert into the base of the distal phalanx of the thumb. It extends the interphalangeal joint and metacarpophalangeal joint of the thumb and is innervated by the posterior interosseous nerve.

Interosseous membrane

The interosseous membrane is a fibrous structure that links the shafts of the radius and ulna. It maintains the interosseous space during pronation and supination, and transmits loads from the radius to the ulna. The interosseous membrane consists of five parts, termed the proximal oblique, dorsal oblique, accessory, central and distal oblique bands ( Fig. 40.3 ). The central band, thought to be the most important, passes between the radius and ulna at a mean angle of 21°; it maintains longitudinal stability, while the distal oblique band contributes to stability of the DRUJ.

The membrane is at risk in two distinct types of injury: the Essex-Lopresti injury and the Galeazzi fracture. The Essex-Lopresti injury was originally described as radial neck fracture with dissociation of the distal radial ulnar joint. However, this cannot occur without rupture of the central condensation of the membrane, which causes longitudinal instability. A Galeazzi fracture is described as a diaphysial fracture of the distal radius with disruption of the distal radio-ulnar joint. Typically with this injury, only the distal oblique band of the interosseous membrane is injured.

Innervation

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