Brachial Plexus

Question 1

Draw the Brachial Plexus

Answer 1

Question 2

What are the upper/lower extremity dermatomes and myotomes

Answer 2

Question 3

C2 Dermatome and Myotome

Answer 3

Dermatome: Temple, forehead, occiput

Myotome: Longus colli, SCM, rectus capitus

Reflex: none

Question 4

C3 Dermatome and Myotome

Answer 4

Dermatome: Entire neck, posterior cheek, temporal area, prolongation forward under mandible

Myotome: Trapezius, splenius capitus

Reflex: None

Question 5

C4 Dermatome and Myotome

Answer 5

Dermatome: Shoulder area, clavicular area, upper scapular area

Myotome: Trapezius, levator scapulae

Relex: None

Question 6

C5 Dermatome and Myotome

Answer 6

Dermatome: Deltoid area, anterior aspect of entire arm to base of thumb

Myotome: Supraspinaturs, infraspinatus, deltoid, biceps

Reflex: BICEPS, brachioradialis

Question 7

C6 Dermatome and Myotome

Answer 7

Dermatome: Anterior arm, radial side of hand to thumb and index finger

Myotome: Beceps, supinator, wrist extensors

Relfex: biceps, BRACHIORADIALIS

Question 8

C7 Dermatome and Myotome

Question 9

C8 Dermatome and Myotome

Question 10

T1 Dermatome and Myotome

Question 11

T4 Dermatome and Myotome

Answer 11

Dermatome: Nipple Line

Myotome:

Question 12

T2 Dermatome and Myotome

Answer 12

Dermatome: Medial side of upper arm to medial elbow, pectoral and midscapular areas.

Myotome: Disk lesions at the upper two thoracic levels do not appear to give rise to root weakness. Weakness of intrinsic muscle of the hand is due to pther pathology (e.g, thoracic outlet pressure, neoplasm of ling, ulnar nerve lesion)

Question 13

Draw the Brachial Plexus

Answer 13

Question 14

Dorsal Scapular Nerve

Answer 14

Origin C5 nerve root of the brachial plexus

Sensory supply None

Motor supply

Levator scapulae (elevates scapula)

Rhomboid major and rhomboid minor (stabilise, retract and medially rotate scapula)

Question 15

Long Thoracic Nerve

Answer 15

Origin: C5, C6 and C7 nerve roots of the brachial plexus

Sensory supply: None

Motor supply: Serratus anterior (protracts and stabilises scapula)

Clinical significance

The long thoracic nerve often crops up in exam questions. An injury to the long thoracic nerve, for example as a result of a sports injury or damage during axillary surgery, results in “winging” of the scapula on examination. The deformity may be visible at rest, and a classic way to elicit or exaggerate it in an OSCE is by asking the patient to push against a wall and looking for abnormal posterior protrusion of the scapula on the affected side.

Question 16

Suprascapular Nerve

Answer 16

Origin: (C5/C6) Superior trunk of the brachial plexus

Sensory supply: Glenohumeral and acromioclavicular joints

Motor supply:

Supraspinatus (stabilises and abducts shoulder)

Infraspinatus (stabilises and externally rotates shoulder)

Question 17

Nerve to Subclavius

Answer 17

Origin: (C6) Superior trunk of the brachial plexus

Sensory supply: None

Motor supply: Subclavius (depresses clavicle and elevates the first rib)

Question 18

Lateral Pectoral Nerve

Answer 18

Origin: (C5/C6/C7) Lateral cord of the brachial plexus

Sensory supply: None to the skin, but it is thought to play an important role in the sensation of chest wall pain, for example after mastectomy or breast implant insertion, and is, therefore, a target for regional nerve blocks

Motor supply

Upper clavicular part of the pectoralis major (flexes, adducts and internally rotates shoulder)

Question 19

Upper Subscapular Nerve

Answer 19

Origin: (C5/C6) Posterior cord of the brachial plexus

Sensory supply: None

Motor supply

Subscapularis (stabilises and internally rotates shoulder)

Question 20

Lower Subscapular Nerve

Answer 20

Origin: (C5/C6) Posterior cord of the brachial plexus

Sensory supply: None

Motor supply

Subscapularis (stabilises and internally rotates shoulder)

Teres major (adducts and internally rotates shoulder, protracts and depresses scapula)

Question 21

Thoracodorsal Nerve

Answer 21

Origin: (C6/C7/C8) Posterior cord of the brachial plexus

Sensory supply: None

Motor supply

Latissimus dorsi (extends, adducts and internally rotates shoulder, externally rotates trunk)

Clinical significance

The thoracodorsal nerve is vulnerable to injury during axillary dissection, for example during lymph node clearance for breast cancer. This results in shoulder movement weakness, which is best elicited on examination by asking the patient to place the dorsum of their hand on the opposite buttock to test extension, adduction and internal rotation. Thankfully, most patients do not suffer from significant loss of function in terms of day-to-day activities, but elderly people may struggle to pull themselves up from a sitting position, and young climbers or bodybuilders are likely to notice significantly reduced performance on the affected side.

Question 22

Medial Pectoral Nerve

Answer 22

Origin: (C8/T1) Medial cord of the brachial plexus

Sensory supply: None to the skin, but may have a role in the sensation of chest wall pain following breast surgery

Motor supply

Pectoralis minor (stabilises scapula, raises ribs during inspiration)

Lower sternocostal part of the pectoralis major (extends, adducts and internally rotates shoulder)

Question 23

Medial Cutaenous Nerve of the Arm

Answer 23

Origin: (T1) Medial cord of the brachial plexus

Sensory supply: Skin of the lower third the of the medial arm

Motor supply

None

Question 24

Medial Cutaneous Nerve of the Forearm

Answer 24

Origin: (C8) Medial cord of the brachial plexus

Sensory supply: Skin over biceps muscle, antecubital fossa and medial forearm

Motor supply: None

Question 25

Musculocutaneous Nerve

Answer 25

Origin: (C5/C6/C7) Lateral cord of the brachial plexus

Sensory supply: Lateral forearm

Motor supply:

Anterior compartment of the arm:

Biceps (flexes elbow, supinates forearm)

Brachialis (flexes elbow)

Coracobrachialis (adducts shoulder, flexes elbow)

Clinical significance

Musculocutaneous nerve injuries are rare, but result in very weak elbow flexion and weak forearm supination which can be very disabling.

CLINICAL FEATURES OF MUSCULOCUTANEOUS NERVE PALSY

SENSORY LOSS

numbness over lateral forearm

MOTOR DEFICIT

paralysis of anterior compartment of arm – very weak elbow flexion and weak forearm supination

absent biceps reflex

DEFORMITY

wasting of anterior compartment of arm

elbow usually held in extension with forearm pronated

Question 26

Axillary Nerve

Answer 26

Origin: (C5/C6) Posterior cord of the brachial plexus

Sensory supply: “Sergeant’s patch” over the lower deltoid

Motor supply

Deltoid (abducts, flexes and extends shoulder)

Teres minor (stabilises and externally rotates shoulder)

Clinical significance

The axillary nerve may be injured by shoulder dislocations or proximal humeral fractures, resulting in numbness over the sergeant’s patch and profound weakness of shoulder abduction from 15-90°. Other examination findings include deltoid wasting and weakness of shoulder flexion, extension and external rotation.

COMMON INJURIES

fracture of surgical neck of humerus

stab wounds to posterior shoulder

anterior shoulder dislocation

pressure of crutches on armpits (“crutch palsy”)

CLINICAL FEATURES OF AXILLARY NERVE PALSY

SENSORY LOSS

numbness over “sergeant’s patch”

MOTOR DEFICIT

paralysis of deltoid – very weak shoulder abduction from 15-90°; weak shoulder flexion and extension

paralysis of teres minor – weak shoulder external rotation

DEFORMITY

wasting of deltoid muscle, making the bones of the shoulder joint very prominent and obvious

shoulder may appear adducted and internally rotated

Question 27

Radial Nerve

Answer 27

Origin: (C5/C6/C7/C8/T1) Posterior cord of the brachial plexus

Sensory supply

Posterior arm and forearm

Lateral ⅔ of the dorsum of the hand

Proximal dorsal aspect of lateral 3½ fingers

Motor supply

The radial nerve supplies the posterior compartment of the arm, which contains triceps (extends and adducts shoulder, extends elbow).

It also supplies the entirety of the posterior compartment of the forearm. This consists of:

Brachioradialis (flexes elbow)

Anconeus (extends elbow, stabilises elbow joint)

Supinator (supinates forearm)

Extensor carpi radialis longus and brevis (extend and abduct wrist)

Extensor carpi ulnaris (extend and adduct wrist)

Extensor digitorum

Extensor pollicis longus and brevis

Extensor indicis

Extensor digiti minimi

Abductor pollicis longus (abducts thumb)

Clinical significance

Radial nerve injuries are commonly due to compression, for example by leaning or lying on the arm for extended periods, excessively tight plaster casts or prolonged tourniquet use. It can also be damaged by fractures of the humerus or radius, or by stab wounds. Radial nerve injury results in loss of innervation to the muscles of the posterior compartments of the arm and forearm. This manifests as numbness in the radial nerve distribution and a “wrist drop” deformity with very weak extension of the elbow, wrist and fingers.

COMMON INJURIES

fractures of proximal humerus, shaft of humerus or radius

stab wounds to antecubital fossa, forearm or wrist

this includes blood tests and venflons!

pressure of crutches on armpits (“crutch palsy“)

the patient falling asleep with arm hanging over the back of a chair, classically whilst drunk (“Saturday night palsy“)

somebody else falling asleep with their head lying on the patient’s arm (“honeymoon palsy“)

excessively tight plaster casts, wristbands or handcuffs

prolonged tourniquet use on upper arm, for example during orthopaedic or plastics procedures

Question 28

Median Nerve

Answer 28

(C5/C6/C7/C8/T1)

Origin

Lateral and medial cords of the brachial plexus

Sensory supply

Thenar eminence, the lateral ⅔ of the palm of the hand

Palmar aspect of lateral 3½ fingers

Dorsal fingertips of lateral 3½ fingers

Motor supply

All muscles of the anterior compartment of forearm EXCEPT flexor carpi ulnaris and the medial two parts of flexor digitorum profundus.

The median nerve, therefore, supplies pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, the lateral two parts of flexor digitorum profundus, flexor pollicis longus and pronator quadratus.

These forearm muscles flex the wrist, the proximal interphalangeal joints of all four fingers and the distal interphalangeal joints of the index and middle fingers. They also pronate the forearm and abduct the wrist.

The median nerve also supplies the LOAF muscles of the hand:

The lateral two lumbricals

Opponens pollicis

Abductor pollicis brevis

Flexor pollicis brevis

The lumbricals flex the MCPJs and extend the IPJs of the index and middle finger.

The muscles of the thenar eminence flex, abduct and oppose the thumb.

Clinical significance

The median nerve is most commonly damaged by compression within the carpal tunnel at the wrist, resulting in numbness of the median nerve distribution to the hand, wasting of the thenar eminence, weak grip strength and a “hand of benediction” deformity due to an inability to flex the index or middle fingers. It can also be injured by supracondylar fractures of the humerus and stab wounds or lacerations to the forearm or wrist.

Question 29

Ulnar Nerve

Answer 29

Origin: (C8/T1)

Medial cord of the brachial plexus

Sensory supply

Hypothenar eminence

Medial ⅓ of the palm of the hand

Palmar aspect of the lateral 1½ fingers

Medial ⅓ of the dorsum of the hand

Dorsal aspect of the medial 1½ fingers

Motor supply

The ulnar nerve supplies just two muscles in the anterior compartment of the forearm

Flexor carpi ulnaris, which flexes and adducts the wrist

The medial two parts of flexor digitorum profundus, which flex the distal interphalangeal joints (DIPJs) of the ring and little fingers.

It also supplies all of the intrinsic muscles of the hand EXCEPT the LOAF muscles supplied by the median nerve. These can be remembered as the HILA muscles:

Hypothenar eminence

Interossei

Medial two lumbricals

Adductor pollicis

The hypothenar eminence consists of opponens digiti minimi, flexor digiti minimi brevis and abductor digiti minimi, which oppose, flex and abduct the little finger respectively.

The palmar interossei adduct the fingers, whilst the dorsal interossei abduct them.

The medial two lumbricals flex the MCPJs and extend the IPJs of the ring and little fingers.

Adductor pollicis adducts the thumb – it is worth noting that this muscle does not form part of the thenar eminence and actually lies deep beneath it as a separate structure.

Clinical significance

The ulnar nerve may be injured by supracondylar fractures of the humerus, medial epicondylar fractures, stab wounds to the forearm or wrist, or compression at either the cubital tunnel in the elbow or Guyon’s canal in the wrist. This results in numbness in the ulnar distribution to the hand, wasting of the hypothenar eminence and intrinsic muscles of the hand, a “claw hand” deformity due to an inability to extend the ring and little fingers, and weak finger abduction and adduction.

Question 30

Cutaneous Nerve supply of hand

Answer 30