9 Anterior and Posterior Forearm

Anterior and Posterior Forearm

Learning Objectives:

By the end of the course students will be able to:

1. Identify the contents of each of the three compartments of the arm and the functions of the muscles within each compartment.
2. Identify the bony landmarks of the humerus, radius, bones of the wrist, and hand
3. Correlate any fractures of the humerus with functional disruptions of associated muscular and neurovascular structures.
4. Describe the movements of the shoulder and elbow joints.
5. Identify spatial relationships of all associated muscular and neurovascular structures within the cubital fossa.
6. Identify the positions of tendons deep to the flexor retinaculum

Reference: Moore, Clinically Oriented Anatomy, chapter 6

Particularly relevant Blue Boxes in Moore:

●Bicipital Myotactic reflex, p. 741

●Rupture of the Tendon of the Long Head of Biceps, p. 741-2

●Interruption of Blood Flow in the Brachial Artery, p. 742

●Injury to the Radial Nerve in the Arm, p. 743

●Injury to the Musculotaneous Nerve, p. 743

●Venipuncture in the Cubital Fossa, p. 743

● Elbow Tendinitis, p. 766

●Median Nerve Injury, p. 768

●Ulnar Nerve Injury, p. 769

●Cubital Tunnel Syndrome, p. 770

● Brachial Plexus block, p. 730

● Read Blue Boxes on p. 768-770

 To access the Netter Presenter Database click here

Grant’s Dissector, 15th Edition, pp 34 – 46; 53 – 57

To access Gray’s Photographic Dissector section on the Forearm click here

To access the Primal Pictures software click here 

Check out the Primal Pictures model of the Arm and Forearm

 

THE FOREARM AND HAND: GENERAL CONSIDERATIONS (Moore 744-770)

The bones of the forearm are the RADIUS and the ULNA (Netter 425).   The ulna’s trochlear notch forms most of the bony articulation at the elbow joint and the radius forms the entire proximal bony articulation at the wrist joint. The INTEROSSEOUS MEMBRANE runs between the two bones, holding them together, and also serves as the origin for many forearm muscles. The fibers of the membrane run in a direction which allows force to be transmitted from the radius to the ulna. This is a protective function and provides some cushioning to prevent injury. The DEEP FASCIA of the forearm and hand divides the forearm into an anterior and posterior compartment. At the wrist, the deep fascia forms a fibrous flexor and extensor retinacula, similar to that of the ankle joint. In the palm, the deep fascia is thick and fibrous; it forms the palmar aponeurosis, an analogous structure to the plantar aponeurosis of the foot.

The BONES OF THE HAND (Netter 439, 443) are divided into the three groups: CARPALS, METACARPALS, and PHALANGES. The metacarpals are, roughly speaking, the bones of the palm, while the phalanges are the bones of the fingers. Note that the phalanges can be referred to as 1st, 2nd, and 3rd or proximal, middle, and distal, respectively.

The MUSCLES (Netter 426, 427, 428, 429, 430) of the forearm consist of the flexors of the anterior forearm compartment, the extensors of the posterior forearm compartment, and the intrinsic muscles of the hand. The forearm flexors originate generally from either the area of the medial humeral epicondyle OR the anterior surfaces of the radius, ulna, and interosseous membrane. The forearm extensors originate generally from either the area of the lateral humeral epicondyle OR the posterior aspects of the radius, ulna, and interosseous membrane. The forearm muscles tend to descend laterally and medially across the forearm as their tendons pass over the anterior and posterior aspects of the wrist, respectively.

DEEP MUSCLE GROUP

Pronator quadratus is a short quadrangular muscle (Netter 426) that originates at the distal ulna and inserts next door on the distal radius. When this muscle contracts, it rolls the radius over the ulna to pronate the hand. There are two deep flexors, the flexor digitorum profundus and the flexor pollicis longus. They both arise from the anterior surfaces of the radius, ulna, and interosseous membrane and their tendons pass superficial to the pronator quadratus muscle. The flexor digitorum profundus inserts onto the base of the distal phalanges of all four fingers, while the flexor pollicis longus inserts on the thumb. These muscles flex the appropriate digits as well as the hand at the wrist.

INTERMEDIATE MUSCLE GROUP

There is only one muscle in this group, the flexor digitorum superficialis (Netter 429). This muscle originates from the radius, ulna (coronoid process), and humerus (medial epicondyle). A tendinous arch connects all these origin points as the muscle merges to form a unified muscle belly. The muscle belly sends four tendons to insert at the base of the second phalanx of each of the four fingers. It functions to flex the fingers and the hand.

The pattern of flexor tendon insertions on the phalanges appears above. Note that the tendons of the flexor digitorum superficialis are superficial to the tendons of the flexor digitorum profundus. The flexor digitorum superficialis tendons split as they attach to the base of the second phalanx, allowing the deep tendons to continue distally and insert at the base of the distal phalanx. The tendons are held closely to the bone by ligamentous sheaths.

 

SUPERFICIAL MUSCLE GROUP

The four muscles of the superficial group originate from a COMMON FLEXOR TENDON (Netter 428), which arises from the medial epicondyle of the humerus.

The pronator teres muscle inserts onto the lateral edge of the radius and works to pronate the forearm. Note that pronator teres has two heads of origin: one from the common flexor tendon (humeral head) and the other from the coronoid process of the ulna (ulnar head). The MEDIAN NERVE passes between the ulnar and humeral heads of the pronator teres.

The flexor carpi radialis inserts on the base of the 2nd and 3rd metacarpals. This muscle flexes and abducts the wrist.

The flexor palmaris longus arises solely from the common flexor tendon and inserts into the palmar aponeurosis (the fibrous thickening of the deep fascia on the palm). This muscle passes across the wrist superficial to the flexor retinaculum. Since it is outside of the retinaculum, this tendon can be made to ‘pop up’ by flexing the hand and then trying to touch, not the tips, but the bases of the 1st and 5th digits. Palmaris longus weakly flexes the hand.

The flexor carpi ulnaris arises from the common flexor tendon and a long line running distally down the posterior ulna. The muscle inserts on the two lateral carpal bones, the HAMATE and the PISIFORM, as well as the base of the 5th metacarpal.  It flexes and adducts the hand.

Clinical Note. The tendons in the anterior forearm near the wrist may be used to locate other structures such as the radial artery which lies lateral to the flexor carpi radialis tendon. A video showing placement of an aterial line in the radial artery may be viewed by clicking here – from the New England Journal of Medicine’s series of Videos in Clinical Medicine.

Muscles of Arm and Flexor Forearm (adapted from Moore Tables 6.9, 6.10, 6.11)

Muscle	Origin	Insertion	Action	Nerve Supply
biceps brachii long head short head	supraglenoid tubercle of scapula coracoid process of scapula	radial tuberosity	flexes arm and forearm, supinates forearm	musculocutaneous
coracobrachialis	coracoid process of scapula	medial surface of humerus	flexes and adducts arm	musculocutaneous
brachialis	distal ½ of anterior surface of humerus	coronoid process of ulna	flexes forearm	musculocutaneous
Triceps brachii long head lateral head medial head	infraglenoid tubercle of scapula posterior surface of humerus, superior to radial groove posterior surface of humerus, inferior to radial groove	olecranon of ulna	extends arm and forearm	radial
brachioradialis	Proximal 2/3rds of lateral supracondylar ridge & anterior surface of intermuscular septum	lateral surface of distal radius just above the styloid process	flexes at the elbow especially when forearm is in midprone position	radial
pronator teres	medial epicondyle of humerus, coronoid process of ulna	lateral aspect of radial shaft	pronates hand, flexes forearm	median
supinator	Deep portion: supinator crest, anular ligament, oblique cord. Superficial portion: lateral epicondyle & radial collateral ligament	upper oblique half of anterior surface of radius and its lateral surface	supinates the forearm	deep branch of radial nerve
flexor carpi radialis	medial epicondyle of humerus-common flexor tendon	Base of 2nd and 3rd metacarpal bones	Flexion of the hand, aid in pronation and abduction of hand	median
palmaris longus	medial epicondyle of humerus -common flexor tendon	flexor retinaculum and palmar aponeurosis	flexes hand and wrinkles skin of palm of hand	median
flexor digitorum superficialis	medial epicondyle of humerus, coronoid process of ulna, anterior border of radius	tendons split to attach to lateral sides of middle phalanges	flexes phalanges, wrist, and forearm	median
flexor carpi ulnaris	medial epicondyle of humerus, olecranon process, and posterior border of ulna	pisiform, hamate, base of 5th metacarpal	flexes and adducts hand	ulnar
flexor pollicis longus	radius and interosseous membrane	base of distal phalanx of thumb	flexes thumb	median
flexor digitorum profundus	upper anterior 3/4ths of ulna and adjacent interosseous membrane	base of distal phalanges of fingers	flexes phalanges	radial half by median ulnar half by ulnar
pronator quadratus	distal anterior aspect of ulna	distal anterior aspect of radius	pronates forearm	median

INNERVATION OF THE FLEXOR FOREARM (Moore 761-763)

The MEDIAN NERVE (Netter 463) innervates a majority of the flexor forearm muscles. There are two exceptions:

1. The ULNAR NERVE (Netter 464) travels distally through the arm along the posterior surface of the medial intermuscular septum. It passes superficially around the medial humeral epicondyle and then through the muscle belly of the flexor carpi ulnaris, which it innervates. This nerve is susceptible to trauma in its superficial course and is known by many as the “funny bone”.

2. The ulnar nerve, as it passes through the forearm, supplies the medial 1/2 of the flexor digitorum profundus muscle.

Therefore, the ULNAR NERVE innervates 1.5 muscles of the flexor forearm, the flexor carpi ulnaris and half of the flexor digitorum profundus. The remaining flexor muscles receive their innervation from the MEDIAN NERVE.

The VASCULAR SUPPLY (Netter 420, 460) to the flexor forearm (Moore 757-760 – look at table 6.12) comes from three important vessels: the RADIAL ARTERY, the ULNAR ARTERY, and the ANTERIOR INTEROSSEOUS ARTERY. Note that the radial artery travels superficially and the ulnar artery travels deep as they descend through the forearm. The radial and ulnar arteries continue into the hand to form the PALMAR ARCHES, the hand’s major blood supply.

 The ulnar artery travels between the flexor digitorum superficialis and profundus. The anterior interosseous artery supplies the deepest flexor muscles (Netter 420). This artery runs deep to flexor  digitorum profundus along the interosseous membrane.

Clinical Note:

The radial artery is often used arterial puncture for blood gas analysis. This video demonstrates the procedure using landmarks in the distal forearm (from the New England Journal of Medicine’s series of Videos in Clinical Medicine)

EXTENSOR FOREARM (Netter 427, 430, 431; Moore 750-757)

There are twelve extensor muscles of the forearm that are found in the posterior compartment. They can be roughly divided into two groups, a SUPERFICIAL and DEEP muscle group. Although the insertions points vary, the origins of the muscles in each group are close together. The superficial muscles originate from the lateral humeral epicondyle, while the deep muscles originate from the posterior surfaces of the radius, ulna, and interosseous membrane of the forearm.

SUPERFICIAL GROUP (Netter 427):

BrachoradialisAnconeusExtensor carpi radialis longusExtensor carpi radialis brevis

      Extensor digiti minimi

Supinator

 

DEEP GROUP

Extensor indicis

Extensor pollicis longus

Extensor pollicis brevis

Abductor pollicis longus

 

THE RADIAL NERVE INNERVATES ALL 12 MUSCLES OF THE EXTENSOR GROUP (Netter 465, 466).

Superficial Group (Netter 430)

Brachioradialis and Anconeus (Netter 431) are both oddballs. The brachioradialis is a member of the posterior compartment, a supposed extensor, yet it is rotated so far around the arm anteriorly, that it FLEXES the elbow. The anconeus muscle extends the elbow and lies “in between” the arm and forearm, thus it is not fully a member of the posterior extensor compartment. The brachioradialis and anconeus muscles are the only muscles of the posterior forearm to act significantly across the elbow joint.

Extersor Carpi Radialis Longus and Brevis and Extensor Carpi Ulnaris are three muscles that extend the hand at the wrist joint, by inserting on the bases of the 2nd, 3rd, and 5th metacarpals, respectively. The extensor carpi radialis longus and brevis also abduct the hand due to their lateral insertion, while the extensor carpi ulnaris adducts the hand. These three muscles are important because they maintain the wrist in extension, which is ‘position of function’. Note the position of the hand while writing or picking up an object – it is extended. The strong ‘grip’ produced by the long flexor tendons also depends on this antagonistic action of wrist extension.  The extensor carpi radialis longus, extensor carpi radialis brevis, and the brachioradialis together make up the “mobile wad”.

 Deep Group (Netter 431)

Supinator  (Netter 426) originates (in mild exception to our general rule) from the lateral humeral epicondyle as well as from the posterior surface of the ulna. It wraps around anteriorly to insert on the radius, which allows for supination of the hand. The supinator is powerfully assisted in this action by the biceps brachii muscle.

Extensor Indicis sends its tendon across the wrist, joining the tendon of the extensor digitorum muscle in the expansion hood of the index finger. This muscle  extends and slightly adducts the index finger.

The Radial nerve innervates every forearm muscle of the posterior compartment. The radial nerve however, divides into a Superficial  (cutaneous) and a Deep (motor) branch. The superficial branch provides cutaneous sensation to portions of the dorsum of the hand (Netter 459).

The deep radial nerve, also known as the posterior interosseous nerve, passes through the supinator muscle to reach the posterior forearm compartment. BEFORE it passes through the supinator, it innervates the two most lateral extensor muscles, the brachioradialis and the extensor carpi radialis longus. AFTER the nerve passes through the supinator, it innervates all nine of the remaining muscles of the extensor forearm.

Muscle	Origin	Insertion	Nerve supply	Action
brachioradialis	Proximal 2/3rds of lateral supracondylar ridge & anterior surface of intermuscular septum	lateral surface of distal radius just above the styloid process	radial	flexes forearm and supinates hand
extensor carpi radialis longus	lateral supracondylar ridge of humerus	Dorsal aspect of base of 2nd metacarpal	radial	Extends and abducts the hand
extensor carpi radialis brevis	lateral epicondyle of humerus	Dorsal aspect of base of 3rd metacarpal	Deep radial	extends and abducts the hand
extensor carpi ulnaris	lateral epicondyle of humerus posterior border of ulna	Dorsal aspect of base of 5th metacarpal	PIN	extends and adducts the hand
extensor digitorum	lateral epicondyle of humerus	extensor expansion over fingers	PIN	extends fingers
extensor digiti minimi	lateral epicondyle of humerus	extensor expansion of little finger	PIN	extends little finger
Anconeus	back of lateral epicondyle of humerus	olecranon process- poster surface of ulna	radial	extends forearm
Supinator	lateral epicondyle of humerus, crest of ulna	proximal third of radius	Deep radial	supinates the forearm
abductor pollicis longus	posterior surface of ulna, middle aspect of radius	base of 1st metacarpal	PIN	abducts thumb
extensor pollicis brevis	middle 1/3rd of radius	base of proximal phalanx of thumb	PIN	extends thumb
extensor pollicis longus	middle 1/3rd ulna & interosseous membrane	base of distal phalanx of thumb	PIN	extends thumb
extensor indicis	posterior surface of ulna	extensor expansion of index finger	PIN	extends index finger

SUMMARY: MUSCLES OF THE FOREARM

Except as noted, all of these muscles receive their innervation from the MEDIAN NERVE: 1) Muscles that ROTATE the radius on the ulna a – Pronator teres b – Pronator quadratus c – Supinator (innervated by deep branch of the radial nerve)   2) Muscles which FLEX the hand at the wrist a- Palmaris longus b- Flexor carpi radialis c- Flexor carpi ulnaris (innervated by ulnar nerve)   3) Muscles which FLEX the digits a – Flexor digitorum superficialis b – Flexor digitorum profundus (1/2 innervated by ulnar nerve) c – Flexor pollicis longus   Except as noted, all of these muscles receive their innervation from the RADIAL NERVE: 4) Muscles that EXTEND the hand at the wrist a – Extensor carpi radialis longus b – Extensor carpi radialis brevis c – Extensor carpi ulnaris   5) Muscles that EXTEND the digits (excl. thumb) a – Extensor digitorum b – Extensor indicis c – Extensor digiti minimi                  6) Muscles that EXTEND or ABDUCT the thumb a – Abductor pollicis longus b – Extensor pollicis brevis c – Extensor pollicis longus

The 19 muscles of the forearm can be grouped functionally, in an easy to remember fashion. The brachioradialis is an exception to the grouping rule; it is innervated by the radial nerve and acts to flex the elbow joint. Without the brachioradialis there are 18 remaining muscles, which can be divided into 6 groups, each containing three muscles. This, functional grouping of muscles is helpful in understanding nerve lesions that may occur within the forearm and hand. For example, if a patient comes in with “wrist drop” (can’t extend hand and digits), you know there must be a lesion of the radial nerve.

Clinical Note: Tennis elbow (lateral epicondylitis) is caused by a chronic inflammation of the origin of the extensor muscles of the forearm from the lateral epicondyle or the humerus as a result of repetitive strain.

Golfers’s elbow (medial epicondylitis) is a painful condition caused by inflammation or irritation in the origin of the flexor muscles of the forearm from the medial epicondyle. Treatment may include injection of glucocorticoids into the inflamed area or avoidance of repetitive flexing of the forearm in order not to compress the ulnar nerve.

 

NERVES OF THE UPPER EXTREMITY (Moore 761-764) 

RADIAL NERVE: C5 – T1 (Netter 465, 466)

The radial nerve is a postaxial nerve that innervates the extensor muscles of the arm and forearm. It provides sensory innervation to the radial half of the dorsum of hand. It arises from posterior cord of brachial plexus and passes anterior to the insertions of latissimus dorsi and teres major muscles. The nerve then passes between the long head of the triceps and the shaft of the humerus through the lateral triangular space to enter the posterior compartment of the arm. It winds inferiorly and laterally in the radial (spiral) groove between the lateral and medial heads of the triceps brachii. The nerve then penetrates the lateral intermuscular septum proximal to the lateral epicondyle, passing deep to the brachioradialis. Near the lateral epicondyle of the humerus, the radial nerve divides into a superficial and deep terminal branch. The superficial branch remains deep within the forearm until it finally ‘pops’ up to pass superficially onto the dorsum of the hand.

The deep branch of the radial nerve, is known as the posterior interosseous nerve after it pierces the supinator to enter the posterior compartment of the forearm. Within the posterior compartment, the deep branch of the radial nerve innervates the extensor muscles. Injury to the radial nerve, or radial nerve palsy, is the most common type of peripheral nerve palsy. In the classic case of radial nerve palsy known as WRIST DROP, a patient will present with a pronated forearm, flexed and adducted hand, and apposed thumb on physical exam.  Complete paralysis, with nerve damage in the axilla, of the radial nerve will result in:

● loss of extension at the elbow, wrist, and metacarpophalangeal joints (Interphalangeal joint extension is preserved by the lumbricals and interossei muscles because they are innervated by the ulnar nerve)

●weakness of thumb abduction from loss of the abductor pollicis longus

● Sensory loss (paresthesia, anesthesia) is generally limited to the dorsum of the  thumb, but may involve  a greater area on the   dorsum of the hand

MEDIAN NERVE: C5 – T1 (Netter 463)

The median nerve is a preaxial nerve that innervates all of the FLEXOR muscles of the FOREARM, with the exception of the flexor carpi ulnaris and half of the flexor digitorum profundus (innervated by the ulnar nerve).  The THENAR MUSCLES and the two radial-most LUMBRICALS are also innervated by the median nerve. Sensory information supplied by the median nerve comes from the lateral palm. Seen on the diagram below (Netter 463), a detailed cutaneous innervation diagram demonstrates the palmar and dorsal areas supplied by the median nerve.

The lateral and a medial cords from the brachial plexus come together to form the median nerve. It travels adjacent to the brachial artery within the medial neurovascular bundle of the arm and emerges medial to the artery in the cubital fossa.  Note the relationship of the bicipital aponeurosis, brachial artery, and median nerve. The nerve passes between the heads of pronator teres and then under the tendinous origin of the digitorum superficialis. The nerve then travels between the superficialis and the deep flexor muscles, innervating most of them. The median nerve passes into the palm under the flexor retinaculum, where it provides both muscular and cutaneous innervation. It provides sensory innervaton to the radial palm and muscular innervation to the 1st and 2nd lumbricals and three thenar muscles. The muscular innervation is provided via the important Recurrent motor branch of the Median Nerve. This nerve is subject to transection by relatively shallow lacerations.

 

Atrophy of the thenar eminence and the unbalanced extension and adduction of the thumb, results in a so-called SIMIAN (Ape) HAND. The median nerve is occasionally compressed as it passes between the two heads of the pronator teres muscle, resulting in Pronator Syndrome. This affects both motor and sensory components. Carpal Tunnel Syndrome is commonly seen (Blue box p. 790) and results from compression of the nerve as it passes deep to the flexor retinaculum. This syndrome can be caused by excessive flexion of the wrist, arthritis, tissue swelling (edema) due to inflammation, and more.  Damage to the median nerve may result in a weak thumb due to thenar atrophy as well as sensory changes in the median nerve distribution.

 

Clinical Note: Injury: The median nerve is well protected by soft tissue and is not commonly damaged. Motor deficits that may manifest in a median nerve lesion include: paralysis of flexion of the wrist, thumb, and radial fingers, loss of grip, loss of pronation, and loss of the ability to oppose the thumb. Note that the proximal phalanges can still be flexed, via the 3rd and 4th lumbricals and all 7 interossei muscles (innervated by the ulnar nerve). A good indication of median nerve damage is loss of the ability to flex the distal phalanx of the fingers. Carpal tunnel Syndrome is caused by compression of he median nerve due to the reduced size of the carpal tunnel, resulting from inflammation of the flexor retinaculum, arthritic changes in the carpal bones, or inflammation or thickening of the synovial sheaths of the flexor tendons. It leads to pain and paresthesia iin the hand in the area supplied by the median nerve (palmar surface of thum, index finger, middle finger and lateral half of ring finger) and may also cause atrophy of the thenar muscles (supplied by the recurrent branch of the median nerve). However, no paresthesia occurs over the thenar eminence of skin because this area is supplied by the palmar cutaneous branch of the median nerve.

 

ULNAR NERVE: C7 – T1 (Netter 464)

Course: The ulnar nerve arises from the medial cord of the brachial plexus and passes posteriorly to the medial intermuscular septum and medial to the triceps.  It passes posterior to the medial condyle of the humerus (‘funny bone’) and into the anterior compartment of the forearm. The nerve passes through the flexor carpi ulnaris muscle, innervating it as it does so, and continues distally down the forearm. It travels adjacent to the ulnar artery between the flexor digitorum superficialis and profundus. The nerve enters the palm of the hand by passing superficial to the flexor retinaculum. In the hand, the nerve divides into superficial and deep branches. The superficial branch supplies cutaneous sensation and motor to the palmaris muscle. The deep nerve branch supplies motor to intrinsic muscles of the hand.

The ulnar nerve is a preaxial nerve, which innervates 1.5 FLEXOR MUSCLES of the FOREARM and most of the MUSCLES OF THE HAND.  The ulnar nerve innervates the flexor carpi ulnaris and 1/2 of flexor digitorum profundus muscle. There are several hand muscles innervated by the ulnar nerve, which include: the hypothenar eminence,  the 7 interossei, lumbricals 3 and 4, palmaris brevis, and adductor pollicis. The median nerve innervates the 3 thenar and 2 lumbrical muscles, and the ulnar nerve innervates the rest of the hand. The ulnar nerve provides sensory innervation to the dorsal and palmar aspects of the ulnar side of the hand.

Clinical Note: Injury: damage to the ulnar nerve may lead to impairment of: extension of middle and distal phalanges, 3rd and 4th fingers, due to loss of interossei and lumbricals adduction of the thumb (Adductor pollicis), adduction and abduction of the fingers (palmar and dorsal interossei) abduction and opposition of the little finger  (hypothenar muscles)

In the case of injury to the ulnar nerve, the palm may become hollow from atrophy of the interosseous muscles. The grip, especially of the ulnar two fingers, will become weak due to atrophy of the hypothenar eminence. The resultant imbalance of the musculature results in a clinical finding known as CLAW HAND. Claw hand refers to hyperextension of the metacarpophalangeal (MP) joints but flexion of the interphalangeal (IP) joints. The interossei and lumbrical muscles tend to flex the MP joint, and when they are lost, the extensors overpower the flexors leading to hyperextension of MP joints. The remaining long flexors, however, are innervated by the median nerve and pull on the IP joints, which gives the hand the “claw” appearance.

Occasionally, one sees the “Saturday Night Drunk Syndrome”, a paralysis (sometimes permanent) of the median and ulnar nerve territories. This often happens when an individual falls asleep with their arm over the back of a chair. Several hours of firm pressure on the medially placed nerves can cut off their blood supply and lead to avascular necrosis and tissue death.

Clinical Note: Cubital tunnel syndrome results from compression on the ulnar nerve in the cubital tunnel behind the mediall epicondyle causing numbness and tingling in the ring and little fingers. The tunnel is formed by the medial epicondyle, ulnar collateral ligemant and the two heads of the flexor carpi ulnaris muscle and transmits the ulnar nerve and superior ulnar collateral or posterior ulnar recurrent artery.

 

MUSCULOCUTANEOUS NERVE: C5 – C7 (Netter 462)

The musculocutaneous nerve is a preaxial nerve that innervates the THREE FLEXOR MUSCLES OF THE ARM.  It continues into the forearm as the lateral cutaneous nerve of the forearm.

Course: It arises from the lateral cord of the brachial plexus and immediately pierces the coracobrachialis muscle. It then travels deep to the biceps brachii, but superficial to brachialis muscle. When it reaches the cubital fossa, it is lateral to the biceps tendon. It passes down the lateral forearm providing cutaneous innervation, running all the way to the base of the thenar eminence Injury: If there is a musculocutaneous lesion, flexion of the forearm will be weakened. Flexion is not completely lost, because the arm can be weakly flexed by the brachioradialis. There will be a relatively small area of anesthesia on the lateral surface of the forearm.

 

AXILLARY NERVE: C5 – C6 (Netter 415, 420)

   This is a postaxial nerve that innervates the deltoid and teres minor muscles. The axillary nerve also controls sensory to the skin over the deltoid muscle.

Course: The nerve arises from the posterior cord of the brachial plexus and passes posteriorly, along with the posterior circumflex artery, through the quadrangular space to the deep surface of the deltoid muscle. (The quadrangular space is bounded by the long head of triceps medially, the lateral head of triceps, laterally, the teres major, superiorly, and the teres minor, inferiorly)

Injury: An axillary nerve lesion results in paralysis of abduction as well as weakness in external rotation of the arm. A patient will be unable to lift their arm to the horizontal plane and anesthesia would be seen over the prominence of the deltoid muscle. A small amount of abduction is possible from the intact action of the supraspinatus.

LONG THORACIC NERVE: C5 – C7 (Netter 413) 

This nerve innervates the serratus anterior muscle. A lesion in this nerve paralyzes the serratus anterior muscle, which results in the characteristic “Winging of the Scapula”. If a patient with long thoracic nerve damage does a push-up or stands facing a wall and pushes against it, the winged scapula will appear. Force on the shoulder girdle is transmitted to the scapula, whose medial edge is no longer firmly attached to the posterior rib cage; this causes the scapula to protrude and resembles a ‘wing’.

SUPRASCAPULAR NERVE: C5 – C6 (Netter 416, 413)

This nerve arises from the superior trunk of the brachial plexus and innervates the supraspinatus and infraspinatus muscles. It passes directly to and across the scapular notch, where it is occasionally damaged by pressure (e.g. carrying heavy loads on the shoulder). Damage to this nerve will cause paralysis or weakness of the supraspinatus and infraspinatus muscles. As a result, initiation of abduction (supraspinatus) and external rotation (infraspinatus) of the arm will be impaired. In order to abduct the arm, a patient must lean to the injured side and swing the arm out laterally. Since the supraspinatus acts to initiate abduction, a patient can use gravity to help initiate abduction enough so that the intact deltoid muscle can take over and abduct the arm as usual.

 

COLLATERAL CIRCULATION OF THE UPPER LIMB

There are three areas of the upper limb where effective and clinically important arterial anastomoses are formed. These are the anastomoses around the SCAPULA – see previous chapter (Netter 415), around the ELBOW (Netter 420), and in the PALM of the HAND and the DIGITS (Netter 453).

ELBOW

The BRACHIAL ARTERY bifurcates into the radial and ulnar arteries once it reaches the cubital fossa. This bifurcation point can be obstructed by thrombi (blood clots) or damaged by trauma (e.g., fracture of the distal humerus). If an obstruction occurs, blood must reach the distal portion of the forearm and hand through the various anastomotic routes (Netter 422).

Although there is biologic variability to the pattern, there is some logic to the blood flow around the elbow:

1) The vessels can be arranged in the corners of a square.

2) All ascending branches, originating distal to the elbow, are called Recurrents.

There are two recurrents from the ulnar artery, one from the radial artery, and one  from the posterior interosseous artery.

3) There are four medial vessels around the elbow joint that are all ‘ulnar’.

There are two descending collaterals from the brachial artery and two ascending  recurrents from the ulnar artery.

4) The superior ulnar collateral and posterior ulnar recurrent travel adjacent to  the ulnar nerve. The anterior branch of the profunda brachii artery and the radial recurrent artery travel close to the radial nerve.

 

 ARTERIAL SUPPLY IN THE PALM OF THE HAND AND DIGITS

In the hands, the interconnections of the arteries are so extensive that when an artery is transected, either by accident or during surgery, both ends must be ligated (tied off).  Note how extensive these anastomoses are in both the palm (the palmar arches) and at the tips of the digits (Netter 453).

The palmar arches are so well interconnected arterially that in the event of trauma or occlusion of either the radial or ulnar artery, sufficient supply to the forearm and hand will usually be maintained by the remaining arteries.

VEINS OF THE UPPER EXTREMITY (Netter 401 403)

The veins of the upper extremity can be divided into 2 categories: SUPERFICIAL and DEEP.  The deep veins accompany the various arteries of the extremity and take their names (vena comitantes). The superficial veins are found in the subcutaneous tissue and do not accompany arteries. The two major superficial veins are the CEPHALIC and BASILIC VEINS. The MEDIAN CUBITAL VEIN connects these two veins near the cubital fossa and is a common site for the drawing blood. Often in the treatment of breast cancer by either radiation or surgery, the axillary vein may be obstructed. If this occurs, the cephalic vein then becomes the principal outflow path from the limb.

LYMPHATICS OF THE UPPER LIMB (Netter 403)

The Superficial Lymphatic Vessels begin in the skin on the palm of the hand and drain into vessels located in the dorsum of the hand; thus, an infection of the palmar aspect of the hand may be observed by a dorsal swelling. The superficial lymphatic vessels ascend up the limb, following the prominent superficial veins to end in the Axillary Nodes. There are fewer DEEP LYMPHATIC VESSELS than the superficial. The deep vessels follow the arteries of the forearm to the brachial artery and drain into the AXILLARY NODES.

Although a few Epitrochlear Nodes are found in the cubital fossa just proximal to the medial humeral epicondyle, the only nodes of importance in the upper limb are the group that form the Axillary Nodes. The axillary nodes are divided into five sets, each draining different territories of the upper limb: anterior, lateral, and posterior chest wall. These nodes drain the entire chest wall above the umbilicus (belly button) as well as the upper limb. In some cases of breast cancer, these nodes are removed because they may contain cancerous cells, which have metastasized from original tumor.

From the axillary nodes all the lymph from the chest wall above the umbilicus and the upper limb drains into the Subclavian Duct. At this point, the lymph drains more or less directly back into the venous circulation.

THE ELBOW JOINT (Netter 422, 423, 424, 426)

The RADIAL and ULNAR COLLATERAL LIGAMENTS run from the lateral and medial humeral epicondyles to the radius and ulna, respectively.  The ANNULAR LIGAMENT holds the head of the radius firmly to the radial notch of the ulna, but allows it to rotate. The ulna is virtually immobile.  It is the rotation of the radius that is completely responsible for producing pronation and supination.

The OLECRANON PROCESS of the ulna acts as a lever arm for the action of triceps. It also prevents hyperextension by filling the olecranon fossa of the posterior humerus. Note the three olecranon bursae in Moore’s 6^th ed. Fig 6.10:

●Subtendinous olecranon bursa (deep to triceps tendon)

●Intratendinous bursa (within the tendon)

●Subcutaneous olecranon bursa (just under the skin of the elbow.

 

THE WRIST JOINT (Netter 439, 440, 441, 442)

The wrist joint is formed by 8 carpal bones. These carpal bones articulate proximally with the distal end of the radius and distally with the proximal ends of the 5 metacarpal bones.  The 8 carpal bones are arranged in roughly two transverse rows of four. It is helpful to regard the capitate bone as the ‘central’ bone and organize the others around it.

 On the palmar aspect of the hand, the carpal bones form a hollowing space. This space is bounded medially by the hook of the hamate and the pisiform, and laterally by the tubercle of the scaphoid and trapezium. These four marginal carpal bones anchor the flexor retinaculum to form the CARPAL TUNNEL. The carpal tunnel is an important region through which all the digital flexor tendons and the median nerve pass (see Blue Box p. 790 – Lesions of the Median Nerve).

Knowledge of the structures of the anterior wrist is important, particularly in emergency room work.  The tendons, vessels, and nerves crossing the wrist are compartmentalized.

On the flexor side, note:

• the flexor carpi ulnaris and radialis attach to the medial and lateral walls of the carpal tunnel
• palmaris longus is superficial to the flexor retinaculum and does not pass within the carpal tunnel
• The flexor digitorum superficialis tendons are superficial to and sequential with the flexor digitorum profundus.
• Ulnar artery and nerve pass deep to flexor carpi ulnaris, but superficial to flexor retinaculum as they enter the palm
• The 5 ‘carpi’ muscles move the hand at the wrist and may be thought of as acting on the corners of an oblong. Between the flexor carpi ulnaris and radialis, extensor carpi ulnaris and radialis (brevis and longus), it takes contraction of any of the adjacent two in order to produce a pure flexion, abduction, extension, or adduction. For example, the two flexors produce flexion and the two ulnaris muscles, flexor and extensor together, produce adduction.