The Anterior and Posterior Forearm

Question 1

Name the muscles of the anterior forearm.

Answer 1

Superficial:
Pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris
Intermediate:
Flexor digitorum superficialis
Deep:
Flexor digitum profundus, flexor pollicis longus, pronator quadratus

Question 2

Which nerves are found in the anterior forearm, and which muscles do they innervate?

Answer 2

Median- pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor pollicis longus, pronator quadratus and lateral half of flexor digitum profundus. Runs distally between FDS and FDP.
Ulnar- flexor carpi ulnaris and medial half of flexor digitorum profundus. Runs distally, deep to FCU (between FCU and FDP).

Question 3

Which arteries are present in the anterior forearm?

Answer 3

Brachial artery splits into:
Radial artery- travels distally and goes through anatomical snuffbox. Deep to brachioradialis, lateral to tendon of flexor carpi radialis.
Ulnar artery- travels distally upon flexor digitorum profundus. Gives off common interosseaous artery.

Question 4

Which veins comprise the deep venous drainage of the upper limb?

Answer 4

Brachial veins split into:
Forearm: radial veins, interosseous veins, ulnar veins.
Which split into:
Hand: deep venous arcade (associated with deep palmar arterial arch), accompanying veins of superficial palmar (arterial) arch.
Veins run alongside arteries.

Question 5

Describe the origin, insertion, action, innervation and blood supply of the flexor carpi radialis.

Answer 5

Origin: common flexor tendon from the medial epicondyle of the humerus
Insertion: base of second and third metacarpals
Action: flexes the wrist, abducts the hand (working with the extensor carpi radialis longus and brevis muscles)
Innervation: median nerve
Blood supply: ulnar artery

Question 6

Describe the origin, insertion, action, innervation and blood supply of the flexor carpi ulnaris.

Answer 6

Origin: common flexor tendon and ulnar head from medial border of olecranon and upper 2/3 of the posterior border of the ulna
Insertion: pisiform, hook of hamate and base of 5th metacarpal
Action: flexes wrist, adducts hand
Innervation: ulnar nerve (passes between the two heads of origin of the flexor carpis ulnaris)
Blood supply: ulnar artery

Question 7

Describe the origin, insertion, action, innervation and blood supply of the flexor digitorum profundus.

Answer 7

Origin: posterior border of the ulna, proximal 2/3 of medial border of ulna, interosseous membrane
Insertion: base of the distal phalanges of digits 2-5
Action: fine motor flexion of the fingers (flexes the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints
Innervation: median nerve via interosseaous branch (lateral half); ulnar nerve (medial half- acts on digits 4 and 5)
Blood supply: ulnar artery; anterior interosseous artery

Question 8

Describe the origin, insertion, action, innervation and blood supply of the flexor digitorum superficialis.

Answer 8

Origin: common flexor tendon (humeroulnar head); middle 1/3 of radius (radial head)
Insertion: shafts of the middle phalanges of digits 2-5
Action: flexion of the metacarpophalangeal and proximal interphalangeal joints
Innervation: median nerve (travels distally in the forearm on the deep surface of the flexor digitorim superficialis)
Blood supply: ulnar artery

Question 9

Describe the origin, insertion, action, innervation and blood supply of the flexor pollicis longus.

Answer 9

Origin: anterior surface of radius and interosseous membrane
Insertion: base of the distal phalanx of the pollex. Tendon of flexor pollicis longus passes through the carpal tunnel with the other long digital flexor tendons and the median nerve.
Action: flexion of the metacarpophalangeal and interphalangeal joints of the pollex
Innervation: median nerve via anterior interosseous branch
Blood supply: anterior interosseous artery

Question 10

Describe the origin, insertion, action, innervation and blood supply of the pronator quadratus.

Answer 10

Origin: medial side of the anterior surface of the distal 1/4 of the ulna
Insertion: anterior surface of the distal 1/4 of the radius
Action: pronation of the forearm (works with pronator teres.
Innervation: median nerve via anterior interosseous branch (same as pronator teres)
Blood supply: anterior interosseous artery
Deepest muscle in the distal forearm

Question 11

Describe the origin, insertion, action, innervation and blood supply of the palmaris longus.

Answer 11

Origin: medial epicondyle of humerus (common flexor tendon)
Insertion: distal half of flexor retinaculum and palmis aponeurosis
Action: vestigial muscle, but can help with flexion of hand at the wrist, and tightens palmar aponeurosis. Don’t really notice if missing (30% people don’t have it)- can take the tendon for a tendon replacement (also helps that tendon is very long)
Innervation: median nerve (good marker for median nerve)
Blood supply: ulnar artery

Question 12

Describe the origin, insertion, action, innervation and blood supply of the pronator teres.

Answer 12

Origin: common flexor tendon and medial side of coronoid process of the ulna
Insertion: midpoint of the lateral side of the shaft of the radius
Action: pronation of the forearm
Innervation: median nerve (passes between the two heads of origin of pronator teres)
Blood supply: ulnar artery; anterior ulnar recurrent artery

Question 13

What is the antebrachial fascia?

Answer 13

The deep fascia of the forearm, or antebrachium, forming a tubular investment around the forearm muscles.
Anterior and posterior thickening forming the extensor retinaculum; immediatel distal but deeper to the palmar carpal ligament, it forms the flexor retinaculum.
Clinical significance: formation of the carpal tunnel through which the median nerve and flexor tendons pass.

Question 14

What is the anterior component of the forearm?

Answer 14

Also called the flexor compartment.

Separated from the posterior compartment by the interosseous membrane.

Question 15

What is the posterior compartment of the forearm?

Answer 15

Also called the extensor compartment.

Separated from the anterior compartment by the interosseous membrane.

Question 16

What is the anatomical snuffbox?

Answer 16

At the base of the thumb; bordered laterally by the tendons of abductor pollicis longus and extensor pollicis brevis, medially by tendon of extensor pollicis longus.
Branches of superficial radial nerve cross the snuffbox; radial artery lies deeply in snuffbox; scaphoid can be palpated there in cases of suspected fracture.

Question 17

What is the extensor retinaculum?

Answer 17

A thickening of the antebrachial fascia at the wrist.

It holds the extensor tendons against the distal radius and ulna to prevent their bow-stringing.

Question 18

What is the interosseous membrane of the forearm?

Answer 18

A fibrous membrane that connects the interosseous borders located on the shafts of the radius and the ulna.
A syndesmosis; its fibres are oriented obliquely downward from the radius toward the ulna; the interosseous membrane is the classic example of a syndesmosis; proximally directed forces from the hand pass through the radius and are transferred to the ulna through the interosseous membrane; marked proximally by the oblique cord.

Question 19

What is the palmar carpal ligament?

Answer 19

A thickening of the antebrachial fascia over the palmar surface of the wrist.
The palmaris longus and ulnar neurovascular bundle pass deep to it, and the flexor retinaculum lies deeper and more distal.

Question 20

What is a synovial bursa?

Answer 20

Bursae are synovial sheaths that stretch along tendons and reduce the friction produced by their movements.

Question 21

Describe the origin, insertion, action, innervation and blood supply of the abductor pollicis longus.

Answer 21

Origin: middle 1/3 of the posterior surface of the radius, interosseous membrane, mid-portion of posterolateral ulna
Insertion: radial side of the base of the 1st metacarpal
Action: abducts the pollex at the carpometacarpal joint
Innervation: deep branch of radial nerve
Blood supply: posterior interosseous artery
Along with extensor pollicis brevis, makes the lateral border of the anatomical snuffbox

Question 22

Describe the origin, insertion, action, innervation and blood supply of the brachioradialis.

Answer 22

Origin: upper 2/3 of the lateral supracondylar ridge of the humerus
Insertion: lateral side of the base of the styloid process of the radius
Action: flexion of the elbow, assists in pronation and supination. Neutral position of muscle is half way between supination and pronation (elbow flexed, thumb up).
Innervation: radial nerve
Blood supply: radial recurrent artery

Question 23

Describe the origin, insertion, action, innervation and blood supply of the extensor carpi radialis longus.

Answer 23

Origin: lower 1/3 of lateral supracondylar ridge of the humerus
Insertion: dorsum of the second metacarpal bone (base)
Action: extension of the wrist, abduction of the hand (works with extensor carpi radialis brevis and flexor carpi radialis in abduction of the hand)
Innervation: radial nerve
Blood supply: radial artery

Question 24

Describe the origin, insertion, action, innervation and blood supply of the extensor carpi radialis brevis.

Answer 24

Origin: common extensor tendon (lateral epicondyle of humerus)
Insertion: dorsum of the third metacarpal bone (base)
Action: extension of the wrist and abduction of the hand (works with extensor carpi radialis longus and flexor carpi radialis)
Innervation: deep radial nerve
Blood supply: radial artery

Question 25

Describe the origin, insertion, action, innervation and blood supply of the extensor carpi ulnaris.

Answer 25

Origin: common extensor tendon and the middle 1/2 of posterior border of the ulna
Insertion: medial side of the base of the 5th metacarpal
Action: extension of the wrist and adduction of the hand (works with the flexor carpi ulnaris)
Innervation: deep radial nerve
Blood supply: ulnar artery

Question 26

Describe the origin, insertion, action, innervation and blood supply of the extensor digiti minimi.

Answer 26

Origin: common extensor tendon (lateral epicondyle of the humerus)
Insertion: joins the extensor digitorum tendon to the 5th digit and inserts into the extensor expansion. Appears to be the ulnar-most portion of extensor digitorum.
Action: extension of the metacarphphalangeal, proximal interphalangeal and distal interphalangeal joints of the 5th digit
Innervation: deep radial nerve
Blood supply: interosseous recurrent artery

Question 27

Describe the origin, insertion, action, innervation and blood supply of the extensor digitorum.

Answer 27

Origin: common extensor tendon (lateral epicondyle of humerus)
Insertion: extensor expansion of digits 2-5. The extensor expansion inserts via a central band on the base of the middle phalanx, while lateral and medial slips insert on the distal phalanx.
Action: extension of the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints of the 2nd to 5th digits; extension of the wrist
Innervation: deep radial nerve
Blood supply: interosseous recurrent artery and posterior interosseous artery

Question 28

Describe the origin, insertion, action, innervation and blood supply of the extensor indicis.

Answer 28

Origin: interosseus membrane and the posterolateral surface of distal ulna
Insertion: its tendon joins the tendon of the extensor digitorum to the second digit. both tendons insert into the extensor expansion
Action: extension of the index finger at the metacarpophalangeal, proximal interphalangeal and distal interphalangeal joints
Innervation:deep radial nerve
Blood supply: posterior interosseous artery
NB.extensor indicis is a deep forearm extensor, whereas extensor digiti minimi is in the superficial layer of extensors

Question 29

Describe the origin, insertion, action, innervation and blood supply of the extensor pollicis brevis.

Answer 29

Origin: interosseous membrane the the posterior surface of the distal radius
Insertion: base of the proximal phalanx of the pollex. Tendon of extensor pollicis brevis and abductor pollicis longus make the lateral border of the anatomical snuffbox.
Action: extension of the pollex at the metacarpophalangeal joint
Innervation: deep radial nerve
Blood supply: posterior interosseous artery

Question 30

Describe the origin, insertion, action, innervation and blood supply of the extensor pollicis longus.

Answer 30

Origin: interosseous membrane and middle part of the posterolateral surface of the ulna
Insertion: base of the distal phalanx of the pollex. Tenson of extensor pollicis longus hooks around the dorsal radial tubercle; it forms the medial border of the anatomical snuffbox.
Action: extension of the pollex at the interphalangeal joint
Innervation: deep radial nerve
Blood supply: posterior interosseous artery

Question 31

Describe the origin, insertion, action, innervation and blood supply of the supinator.

Answer 31

Origin: lateral epicondyle of the humerus, supinator crest and fossa of the ulna, radial collateral ligament, annular ligament
Insertion: lateral side of proximal 1/3 of the radius
Action: supinates the forearm
Innervation: deep radial nerve (passes through the supinator to reach the posterior compartment of the forearm)
Blood supply: recurrent interosseous artery

Question 32

Which arteries are present in the forearm?

Answer 32

Radial, ulnar, interosseous anterior, interosseus common, interosseus posterior

Question 33

Describe the radial artery (source, branches, supply).

Answer 33

Source: brachial artery (usually arises at elbow level)
Branches: radial recurrent artery, palmar carpal branch, superficial palmar branch, dorsal carpal branch, 1st dorsal metacarpal artery, princeps pollicis artery, radialis indicis artery, deep palmar arterial arch
Supplies: posterior elbow, posterior forearm, posterior hand, deep portion of palmar side of the hand, thumb

Question 34

Describe the ulnar artery (source, branches, supply).

Answer 34

Source: brachial artery (usually arises at elbow level)
Branches: anterior ulnar recurrent artery, posterior ulnar recurrent artery, common interosseous artery, palmar carpal branch, dorsal carpal branch, deep palmar branch, superficial palmar arterial arch
Supplies: medial side of the anterior forearm, posterior forearm, superficial palm, fingers

Question 35

Describe the anterior interosseous artery (source, branches, supply).

Answer 35

Source: common interosseous artery.
Branches: muscular branches, artery of the median nerve
Supplies: flexor pollicis longus muscle, flexor digitorum profundus muscle, pronator quadratus muscle, radius, ulna, carpal bones (Pierces the interosseous membrane at its distal end to reach the dorsal carpal anastomosis)

Question 36

Describe the common interosseous artery (source, branches, supply).

Answer 36

Source: ulnar artery
Branches: anterior interosseous artery, posterior interosseous artery
Supplies: deep structures of the forearm (the deep forearm flexor and deep forearm extensor muscles)

Question 37

Describe the posterior interosseous artery (source, branches, supply).

Answer 37

Source: common interosseous artery
Branches: interosseous recurrent artery
Supplies: muscles of the posterior (extensor) forearm compartment: supinator muscle, abductor pollicis longus muscle, extensor pollicis longus muscle, extensor pollicis brevis muscle, extensor indicis muscle. Passes proximal to the interosseous membrane to reach the extensor compartment of the forearm.

Question 38

Name the nerves of the forearm.

Answer 38

Ulnar nerve, radial nerve, superficial radial nerve, deep radial nerve, median nerve, anterior interosseous nerve, posterior interosseous nerve.

Question 39

Describe the anterior interosseous nerve (source, branches, motor function, sensory function).

Answer 39

Source: median nerve
Branches: none named
Motor function: flexor pollicis longus muscle, radial half of flexor digitorum profundus muscle, pronator quadratus muscle
Sensory function: none
NB. Courses along the anterior surface of the interosseous membrane

Question 40

Describe the posterior interosseous nerve (source, branches, motor function, sensory function).

Answer 40

Source: deep radial nerve
Branches: none named
Motor function: some authors say none, others say the deep posterior forearm muscles
Sensory function: proprioception to the wrist joint
NB. There is variability in the definition of this nerve; for some, deep radial and posterior interosseous are synonymous; others define this nerve as the articular branch to the wrist from the deep radial

Question 41

Describe the median nerve (source, branches, motor function, sensory function).

Answer 41

Source: lateral and medial cords of the brachial plexus
Branches: anterior interosseous nerve, palmar branch, recurrent (motor) branch, common palmar digital nerves (for digits 1-3)
Motor function: pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor digitorum profundus (radial half), flexor pollicis longus, pronator quadratus, abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, lateral 2 lumbrical muscles
Sensory function: skin of the radial half of the palm and palmar side of the lateral 3 1/2 digits (and nail bed for these digits)

Question 42

Describe the radial nerve (source, branches, motor function, sensory function).

Answer 42

Source: posterior cord of the brachial plexus
Branches: posterior brachial cutaneous nerve, inferior lateral brachial cutaneous nerve, posterior antebrachial cutaneous nerve, superficial and deep branches
Motor function: muscles of the posterior arm: triceps brachii, anconeus; muscles of the posterior forearm: brachioradialis, extensor carpi ulnaris, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, supinator, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, extensor indicis
Sensory function: skin of the posterior arm, forearm and hand

Question 43

Describe the deep radial nerve (source, branches, motor function, sensory function).

Answer 43

Source: radial nerve
Branches: posterior interosseous nerve
Motor function: extensor carpi radialis brevis, supinator, extensor digitorum, extensor digiti minimi, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, extensor indicis
Sensory function: none- no cutaneous branches
NB. Deep radial nerve passes through the supinator; some authors believe that the posterior interosseous nerve and the deep radial nerve are synonymous, others say that when the deep radial nerve emerges from the supinator in the posterior forearm it becomes the posterior interosseous nerve, and others say that the deep radial nerve does not become the posterior interosseous nerve until after its last muscular branch has been given off

Question 44

Describe the superficial radial nerve (source, branches, motor function, sensory function).

Answer 44

Source: radial nerve
Branches: dorsal digital branches
Motor function: sympathetic motor for the skin
Sensory function: skin of the posterolateral wrist and hand; dorsum of the lateral 2 1/2 digits (excluding the skin over the distal phalanx/nail bed)
NB. superficial radial nerve is located deep to the brachioradialis muscle

Question 45

Describe the ulnar nerve (source, branches, motor function, sensory function).

Answer 45

Source: medial cord of the brachial plexus
Branches: palmar cutaneous branch, dorsal branch, superficial and deep branches
Motor function: flexor carpi ulnaris, flexor digitorum profundus (ulnar half), abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi, ulnar 2 lumbrical muscles, palmar and dorsal interosseous muscles (motor muscle to most muscles of the hand)
Sensory function: skin of the medial side of the wrist and hand; skin of the medial 1 1/2 digits

Question 46

What is a Colles fracture?

Answer 46

Most common fracture of the forearm. The distal end of the radius is broken, and distal fragment is displaced dorsally and is often comminuted (broken into pieces). The fracture results from forced extension of the hand, usually as the result of trying to ease a fall by outstretching the upper limb.

Question 47

What is tennis elbow?

Answer 47

Also called elbow tendinitis, it is due to repetitive use of the superficial extensor muscles of the forearm. The pain is felt on the lateral epicondyle and radiates down the posterior surface of the forearm. Patients with this condition will often feel pain when they open a door or lift a glass. The repeated forceful flexion and extension of the wrist strains the attachment of the common tendon, producing inflammation of the periosteum of the lateral epicondyle and the common extensor attachment of the muscles.

Question 48

What is epicondylitis?

Answer 48

Inflammation of the epicondyle or of the tissues adjoining the epicondyle of the humerus. Lateral epicondylitis is also referred to as “tennis elbow”.

Question 49

Describe a scaphoid fracture/ avascular necrosis.

Answer 49

The scaphoid is the most frequently fractured carpal bone, and injury to this bone is the most common wrist injury. Pain occurs primarly during extension and abduction of the hand, and is felt on the lateral side of the wrist. Because of poor blood supply to the proximal part of the scaphoid, union of the fractured parts may take several months. Avascular necrosis of the proximal fragment of the scaphoid may occur and produce degenerative joint disease of the wrist. In some cases, it is necessary to fuse the carpals surgically.

Question 50

What is ‘wrist drop’?

Answer 50

Wrist drop is a sign of radial nerve injury that has occurred proximal to the elbow.
There are two common characteristic sites of damage:
Axilla – injured via humeral dislocations or fractures of the proximal humerus.
Radial groove of the humurus - injured via a humeral shaft fracture.
The radial nerve innervates all muscles in the extensor compartment of the forearm. In the event of a radial nerve lesion, these muscles are paralysed. The muscles that flex the wrist are innervated by the median nerve, and thus are unaffected. The tone of the flexor muscles produces unopposed flexion at the wrist joint – wrist drop.

Question 51

Name the muscles of the posterior forearm.

Answer 51

Superficial (7 muscles): extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, extensor digiti minimi, brachioradialis, extensor carpi radialis longus, aconeus.
Deep (5 muscles): supinator, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, extensor indicis.

Question 52

Describe the anconeus muscle (origin, insertion, action, innervation, blood supply).

Answer 52

Origin: lateral epicondyle of the humerus,
Insertion: posterior and lateral part of the olecranon.
Actions: Moves the ulna during pronation and extends at the elbow joint
Innervation: Radial nerve
Blood supply: Interosseous recurrent branch of the posterior interosseous artery; middle collateral artery from the deep brachial artery.
NB. The aconeus is situated medially and superiorly in the extensor compartment of the forearm. It is blended with the fibres of the triceps brachii, and the two muscles can be indistinguishable.