Radial Nerve Flashcards
What is the radial nerve?
A major peripheral nerve of the upper limb
What are the nerve roots of the radial nerve?
C5-T1
What is the sensory function of the radial nerve?
It innervates most of the skin of the posterior side of the forearm, and the dorsal surface of the lateral side of the palm, and lateral three and a half digits
What muscles does the radial nerve innervate?
The triceps brachii
The majority of extensor muscles in the forearm
What is the triceps brachii responsible for?
Extension at the elbow
What are the extensor muscles in the forearm responsible for?
Extension of the wrist and fingers, and supination of the forearm
What is the radial nerve formed from?
Continuation of the posterior cord of the brachial plexus, containing nerve fibres from all 5 roots (C5-T1)
What course does the radial nerve take?
Arises in the axilla, exiting posteriorly to the brachial artery. Here it supplies branches to the long and medial heads of the triceps brachii.
The radial nerve then descends down the arm
As it moves inferiorly, the radial nerve wraps around the humerus in a lateral direction, and gives a branch to the lateral head of the triceps brachii
Where does the radial nerve travel when descending down the arm?
In a shallow depression on the surface of the humerus known as the radial groove
What is the radial nerve accompanied by during its course in the arm?
The brachial artery
How does the radial nerve enter the forearm?
It moves anteriorly over the lateral epicondyle of the humerus, through the cubital fossa
Where does the radial nerve terminate?
Within the forearm
How does the radial nerve terminate?
By dividing into two branches
What two branches does the radial nerve divide into?
Deep branch
Superficial branch
What does the deep branch of the radial nerve do?
It is a motor branch, and so innervates the muscles in the posterior compartment of the forearm
What does the superficial branch of the radial nerve do?
It is a sensory branch, and so contributes to the cutaneous innervation of the hands and fingers
What muscles does the radial nerve innervate in the arm?
The three heads of the triceps brachii
What does the triceps brachii do?
Performs extension at the elbow
What muscles does the deep branch of the radial nerve innervate in the forearm?
Muscles in the posterior compartment of the forearm
What do muscles in the posterior compartment of the forearm generally do?
Extend at the wrist and finger joints
What branches of the radial nerve provide cutaneous innervation to the skin?
Lower lateral cutaneous nerve of arm
Posterior cutaneous nerve of arm
Posterior cutaneous nerve of forearm
Superficial branch of radial nerve
What does the lower lateral cutaneous nerve of arm innervate?
The lateral aspect of the upper arm, below the deltoid muscle
What does the posterior cutaneous nerve of the arm innervate?
Posterior surface of upper arm
What does the posterior cutaneous nerve of forearm innervate?
Strip of skin down the middle of posterior forearm
What does the superficial branch of the radial nerve innervate?
The dorsal surface of the lateral three and a half digits, and their associated palm area
What are lesions of the radial nerve broadly categorised into?
Four groups
What does the group that a radial nerve lesion is classified into dependant on?
Where the damage has occurred, and what components of the nerve have been affected
What are the four categories of damage to the radial nerve?
In the axilla
In the radial groove
Deep branch of radial nerve
Superficial branch of radial nerve
How does radial nerve damage in the axilla commonly occur?
Dislocation of the humerus at the glenohumeral joint
Fractures of the proximal humerus
Via excessive pressure on the axilla
What motor functions are affected by radial nerve damage in the axilla?
Triceps brachii and muscles in the posterior compartment are paralysed, and so the patient is unable to extend the forearm, wrist and fingers.
Unopposed flexion of the wrist occurs, known as wrist drop
What sensory functions are affected by radial nerve damage in the axilla?
All four cutaneous branches of the radial nerve are affected, and so there will be a loss of sensation over the lateral and posterior upper arm, posterior forearm, and dorsal surfaces of the lateral three and a half digits
How does damage to the radial nerve in the radial groove commonly occur?
Fracture in the shaft of the humerus, damaging the radial nerve when its bound in the radial groove
How does damage to the radial nerve in the radial groove affect motor function?
The triceps brachii may be weakened, but it’s not paralysed.
The deep branch of the radial nerve is affected, to muscles in the posterior compartment of the forearm are paralysed
Patient unable to extend wrist and fingers
Wrist drop
How does damage to the radial nerve in the radial groove affect sensory function?
Superficial branch of radial nerve will be damaged, resulting in sensory loss on the dorsal surface of the lateral three and a half digits, and their associated palm area
How does damage to the deep branch of the radial nerve commonly occur?
Fractures of the radial head, or posterior dislocation of the radius at the elbow joint
How are motor functions affected with damage to the deep branch of the radial nerve?
Muscles in the posterior compartment of the forearm are affected, except for the supinator and extensor carpi radialis longus
Does wrist drop occur in damage to the deep branch of the radial nerve?
No
Why does wrist drop not occur in damage to the deep branch of the radial nerve?
Because the extensor carpi radialis longus, which is unaffected, is a strong extensor in the wrist
How are sensory functions affected in damage to the deep branch of the radial nerve?
They are not, as it’s a motor nerve
How does damage to the superficial branch of the radial nerve commonly occur?
Stabbing or laceration of the forearm
How does damage to the superficial branch of the radial nerve affect motor functions?
It doesn’t, as its a sensory nerve
How does damage to the superficial branch of the radial nerve affect sensory functions?
There will be sensory loss affecting the dorsal surface of the lateral three and a half digits and their associated palm area
