MSK Nerves of the upper limb

Question 1

What are the roots of the brachial plexus?

Answer 1

The roots are formed by spinal nerves C5-T1
At each vertebral level the paired nerves leave the spinal chord via the intervertebral foramina
The roots of the brachial plexus are made up of the anterior divisions

Question 2

What are the trunks of the brachial plexus?

Answer 2

At the base of the neck the roots converge to 3 trunks:
Superior - C5 C6
Middle - C7
Inferior - C8 T1

Question 3

What are the divisions of the brachial plexus?

Answer 3

Each trunks divides into 2 branches - 1 division travels anteriorly and the other posteriorly
This results in 3 anterior and 3 posterior nerve fibres which pass into the axilla region

Question 4

What are the cords of the brachial plexus?

Answer 4

One the anterior and posterior divisions have entered the axilla they recombine to form 3 cords. These are named by their position relative to the AXILLARY ARTERY.

Lateral cord: anterior division of superior trunk, anterior division of middle trunk
Medial cord: anterior division of inferior trunk
Posterior cord: posterior division of superior trunk, posterior division of middle trunk, posterior division of inferior trunk

Question 5

What are the major branches of the brachial plexus?

just a list and roots

Answer 5

The cords give rise to the 5 major branches:

Musculocutaneous nerve C5 6 7 
Axillary nerve C5 6 
Median nerve C5 6 7 8 T1
Radial nerve C5 6 7 8 T1
Ulnar nerve C8 T1

Question 6

During dissection, how can you identify the brachial plexus nerves?

Answer 6

Look for the ‘M’ shaped structure
This is formed by the musculocutaneous, median and ulnar nerves and is arranged around the brachial artery
It can help you to get your bearings

Question 7

State the 2 major injuries that can occur to the brachial plexus and how they occur?

Answer 7

Upper brachial plexus injury - Erbs palsy
Occurs when there is an excessive angle between the neck and shoulder as a result of pulling a baby by the arm during birth, or shoulder trauma (e.g. falling off motor bike)

Lower brachial plexus injury - Klumpke palsy
Occurs from excessive abduction of arm e.g. person catching a branch as they fall from a tree (rarer than erbs)

Question 8

Describe Erbs palsy

Answer 8

The nerves damage are those derived from C5-6
There is paralysis of supra/infraspinatus, subclavius, BBC, deltoid and teres minor
Movements are lost or greatly weakened - shoulder abduction, lat rotation of arm, supination of forearm and shoulder flexion
There is loss of sensory function down lateral arm

The characteristic position is waiters tip, where the arm hangs limb and is medially rotated by unopposed action of pec major

Question 9

Describe klumpke palsy

Answer 9

The nerves damaged are those from T1 (median and ulna)
All the small muscles of the hand are paralysed
There is loss of sensation down the medial side of the arm

The MCP joints are hyperextended and the IP joints are flexed giving the hand a clawed appearance

Question 10

What is the motor and sensory function of the musculocutaneous nerve?

Answer 10

Motor functions: BBC

Sensory functions: skin of lateral forearm (gives rise to lateral cutaneous nerve)

Question 11

What is the anatomical course of the musculocutaneous nerve?

Answer 11

The musculocutaneous nerve leaves the axilla and pierces the coracobrachialis muscle, it then passes down the arm anterior to brachialis and deep to biceps brachii.

The nerve then emerges lateral to the biceps tendon and continues into the forearm as the lateral cutaneous nerve.

Question 12

What happens if there is a lesion to the musculocutaneous nerve and how does this occur?

Answer 12

Relatively uncommon because musculocutaneous nerve well protected within the axilla. Most common cause is stab wound to the axilla.

Paralyses BBC so shoulder flexion weakened (can still occur due to pec major) elbow flexion weakened (can still occur due to brachioradialis) supination greatly weakened (can still occur due to supinator)

Loss of sensation of lateral forearm

Question 13

What is the motor and sensory function of the axillary nerve?

Answer 13

Motor function: teres minor and deltoid

Sensory function: regimental badge area

Question 14

What is the anatomical course of the axillary nerve?

Answer 14

Axillary nerve lies posteriorly to the axillary artery and anteriorly to subscapularis. Exits axilla posteriorly by the quadrangular space (accompanied by posterior circumflex humeral artery)

Question 15

What are the boundaries of the quadrangular space and what structures pass through it?

Answer 15

Superior border - subscapularis and teres minor
Inferior border - teres major
Medially - long head of triceps
Laterally - surgical neck of humerus

The axillary artery and posterior circumflex humeral artery pass through the quadrangular space

Question 16

What happens if there is a lesion to the axillary nerve and how does this occur?

Answer 16

Most commonly damaged by a fracture to surgical neck of humerus

Paralyses deltoid and teres minor so patient unable to abduct arm

Loss of sensation to regimental badge area

In long standing cases the deltoid readily atrophies so the greater tubercle can be palpated

Question 17

What is the motor and sensory function of the median nerve?

Answer 17

Motor functions: flexor muscles of anterior forearm (except FCU and part of FDP). Thenar muscles and lateral 2 lumbricals

Sensory functions: lateral palm and lateral 3 1/2 digits (finger tips)

Question 18

What is the anatomical course of the median nerve?

Answer 18

Descends down arm lateral to brachial artery then half way down crosses artery to become medial. Enters anterior forearm via cubital fossa

Travels between flexor digitorum proudness and flexor digitorum superficial, gives rise to 2 branches - anterior interosseous nerve (supplies deep muscles) and palmar cutaneous nerve (skin of lateral palm) enters the hand via the carpal tunnel and divides into 2 branches - recurrent branch (thenar muscles) and palmar digital branch (fingertips of lat 3 1/2)

Question 19

What happens if there is a lesion to the median nerve and how does this occur?

Answer 19

Damaged at the elbow by supracondylar fracture of humerus
Flexors and pronators of forearm paralysed so constantly supinated with weak flexion. Thumb flexion prevented and lateral 2 lumbricals paralysed

Loss of sensation of palm and fingertips of lateral 3 1/2

Atrophy of thenar muscles, hand of benediction (when tries to make a fist)

Damaged at the wrist by lacerations just proximal to flexor retinaculum
Thenar and lateral 2 lumbricals paralysed so no opposition of thumb or flexion of index and middle fingers

Sensory and signs same as injury at elbow

Question 20

What is the motor and sensory function of the radial nerve?

Answer 20

Motory function: Tricpes, extensors in posterior forearm
Sensory function:
- posterior cutaneous nerve, posterior upper arm
- posterior cutaneous nerve of forearm, strip of posterior forearm
- superficial branch, dorsal surface of lateral 3 1/2 digits

Question 21

What is the anatomical course of the radial nerve?

Answer 21

The nerve arises in the axilla exiting posteriorly to the brachial artery. It descends down the arm in the radial groove of the humerus. During its course down the arm it is accompanied by the deep branch of the brachial artery.

The nerve moves anteriorly over the lateral epicondyle through the cubital fossa. In the forearm the nerve splits into 2 branches -deep branch (motor) and superficial branch (sensory)

Question 22

What happens if there is a lesion to the radial nerve and how does this occur? (hint there are 4 types)

Answer 22

Injury in the axilla:
Can occur from dislocation of humerus at glenohumeral joint or fracture of proximal humerus
Triceps and posterior forearm muscles paralysed resulting in flexed arms and wrist drop.
Loss of sensation over lateral and posterior upper arm, posterior forearm and dorsal surface of lat 3 1/2 fingers

Injury in the radial groove:
Occurs from a fracture of the humeral shaft
Triceps weakend, muscles of posterior forearm paralysed so wrist drop. Sensory loss of dorsal surface of lateral 3 1/2 digits

Injury to deep branch of radial nerve:
Fractures of radial head or radial dislocation
Muscles in posterior forearm affected (except extensor carpi radials longs and supinator, so no wrist drop)

Injury to superficial branch of radial nerve:
Stabbing of forearm.
No loss of motor function as it is a sensory nerve. Sensor loss of dorsal surface of lateral 3 1/2 digits

Question 23

What is the motor and sensory function of the ulnar nerve?

Answer 23

Motor functions: Hand muscles except thenar muscles and lat 2 lumbricals. Flexor carpi ulnaris and some flexor digitorum profundus
Sensory functions: anterior and posterior of medial 1 1/2 fingers with associated palm area

• palmar cutaneous branch, skin of medial 1/2 palm
• dorsal cutaneous branch, skin of medial 1 1/2 fingers and associated palm area
• superficial branch, palmar surface of medial 1 1/2 fingers

Question 24

What is the anatomical course of the ulnar nerve?

Answer 24

Descends down medial side of upper arm and passes posterior to medial epicon§dyle (easily palpable at this site and vulnerable to injury).
Ulnar nerve pierces the heads of the flexor carpi ulnas and travels alongside the ulna, gives rise to 3 branches.
Enters hand superficially to the flexor retinaculum

Question 25

What happens if there is a lesion to the ulnar nerve and how does this occur?

Answer 25

Damage at the elbow:
Most commonly due to fracture of medial epicondyle
FCU and some of FDP paralysed. Flexion can occur but hand also abducts. Interossei paralysed to no add/abd of fingers.
All sensory areas affected
Patient cannot grip paper between fingers

Damage at the wrist:
Due to lacerations at the wrist
Interossei paralysed so no add/abd of fingers. Medial 2 lumbricals paralysed so little and ring affected greatly
Sensory loss of palmar side of medial 1 1/2 fingers
Patient cannot grip paper between fingers, in long standing cases there is ulnar claw

Question 26

What is the ulnar paradox?

Answer 26

Occurs when the ulnar nerve damage occurs more proximally at the elbow
The medial 2 lumbricals are still paralysed, along with the medial half of FDP and FCU.
The ulnar claw develops with a key difference - there will only be flexion at the proximal IP joints producing a less evident claw