Question-3: Describe Radial Nerve Under
Table of Contents
1. Radial Nerve Root value,
2. Radial Nerve Course and Relations,
3. Radial Nerve Branches, and
4. Radial Nerve Applied Anatomy.
Answer:
Radial Nerve Introduction:
It is the nerve of the extensor compartment of the arm and forearm, supplying the skin over them and on the dorsum of the hand. It is the direct continuation of the posterior cord of the brachial plexus. It is the largest branch of the whole brachial plexus.
1. Radial Nerve Root value
It arises from the posterior cord of the brachial plexus carrying fibres from the ventral roots of spinal nerves C5, C6, C7, C8 and T1.
Read And Learn More: Anatomy Notes And Important Questions and Answers
2. Radial Nerve Course and relations
It arises from the posterior cord of the brachial plexus. The posterior cord lies posterior to the 2nd part of the axillary artery and the radial nerve lies posterior to the 3rd part of the axillary artery. It lies medial to the axillary nerve.
1. Course of the radial nerve in the lower part of the axilla. The nerve passes downwards. It crosses the lower border of the posterior axillary wall. It includes crossing of the glistening tendon of latissimus dorsi, and subscapularis. Here it has the following relations.
- Anteriorly: Axillary artery and pectoralis major.
- Posteriorly: Subscapularis, teres major and latissimus dorsi.
- Medially: Axillary vein
- Laterally: Coracobrachialis muscle.
It passes through lower lar space and enters the radial groove along with the profunda brachial artery.
2. Course of the radial nerve in the arm: It enters the arm. It has the following relations. It is
- Posterior to the brachial artery,
- Medial to the humerus, and
- Anterior to the long head of the triceps.
3. Course of the radial nerve in the radial groove
- The nerve passes obliquely across the back of the humerus.
- The course is from medial to lateral in a shallow groove and between the long and medial heads of the triceps. It passes along with the profunda brachial artery.
- At the lower end of the radial groove, it pierces the lateral intermuscular septum and enters into the anterior or flexor compartment of the arm.
- In the flexor compartment of the lower arm, it descends in the intermuscular slit.
4. Course and relations of the radial nerve in the intermuscular slit
- In the upper part, it lies between the brachialis medially and brachioradialis laterally.
- In the lower part, it lies the brachialis medially and extensor carpi radialis longus laterally.
5. Course of the radial nerve in the forearm: At the level of the lateral epicondyle, it gives off two terminal branches. The branches are
- Superficial terminal branch, and
- Deep terminal branch. It is called the posterior interosseous nerve.
1. Superficial terminal branch. It is entirely cutaneous in its distribution. It supplies to the dorsum of the hand and fingers.
1. Course of the superficial terminal branch of radial nerve
In front of the forearm:
- It leaves the cubital fossa and enters the lateral side of the forearm.
- In the upper 2/3rd, it is accompanied by radial vessels.
- At the junction of the upper 2/3rd and lower 1/3rd, it runs laterally and reaches the posterolateral aspect of the forearm.
In hand
It reaches the wrist and travels in the roof of the anatomical snuffbox
2. Posterior interosseous branch.
1. Course of posterior interosseous nerve: This leaves the cubital fossa by piercing the supinator muscle. It enters the back of the forearm.
At the cubital fossa, it runs downwards on the surface of
- Supinator,
- Pronator teres, and
- Flexor digitorum superficialis.
At the forearm, it runs on the lateral side of the forearm under the cover of the brachioradialis.
In the middle 1/3rd of the forearm, it lies lateral to the radial artery.
In the extensor compartment of the lower part of the forearm.
It then leaves the flexor compartment of the forearm and winds around the lower end of the radius deep to the tendon of the brachioradialis. It crosses the structures forming an anatomical snuffbox. They are
- Abductor pollicis longus,
- Extensor pollicis brevis, and
- Extensor pollicis longus.
Note: On the posterior surface of the interosseous membrane, it enlarges into a pseudo-ganglion. It breaks into 2 or 3 branches which can be rolled on the surface of the tautened tendon of the extensor pollicis longus. They are distributed to the radial 2/3rd of the dorsum of the hand and proximal parts of the dorsal surfaces of the thumb and lateral 21/2 or 31/2 fingers.
3. Radial Nerve Branches of the radial nerve can be described as
- Collateral branches
- Terminal branches
1. Collateral branches
- Branches above the radial groove,
- In the radial groove, and
- Below the radial groove.
Branches above the groove are motor, sensory and articular.
1. Motor branches are to the
- Long, and
- The medial head of the triceps. It is called the ulnar collateral nerve.
2. The sensory branch is the posterior cutaneous nerve of the arm.
3. The articular branch supplies the elbow joint.
Branches in the groove are motor and sensory.
1. Motor branches are to
Lateral, and
The medial head of the triceps. The branch to the medial head of the triceps goes deep and supplies the anconeus.
2. There are two sensory branches given in the groove: To the skin of
- Arm, and
- Forearm.
1. The cutaneous branch given in the arm is called the lower lateral cutaneous nerve of the arm. It pierces the lateral head of the triceps to supply the skin over the lateral surface of the arm up to the elbow.
2. The cutaneous nerve of the forearm is called the posterior cutaneous nerve of the forearm. It runs straight behind the elbow to supply a strip of skin over the extensor surface of the forearm up to the wrist.
The branches given below the groove are
1. Motor to
- Brachioradialis and
- Extensor carpi radialis longus,
2. Proprioceptive to the lateral part of the brachialis.
2. Terminal branches: The radial nerve divides at the level of the lateral epicondyle into superficial and deep terminal branches (posterior interosseous nerve).
The superficial branch is the continuation of the main nerve. It is purely cutaneous and is distributed to the skin of
1. Lateral 1/2 of the dorsum of the hand
2. Proximal parts of the dorsal surface of the
- Thumb,
- Index fingers, and
- Lateral ½ of the middle finger.
A deep branch is motor and is called the posterior interosseous nerve. It supplies
1.Muscles in cubital fossa
Extensor carpi radialis brevis, and
Supinator
2. Muscles in the extensor compartment (7 muscles). They are conveniently divided into two groups for easy recollection.
1.1st group includes
Extensor muscles reaching wrist, index finger, digits and little finger. They are
- Extensor carpi ulnaris,
- Extensor indices,
- Extensor digitorum, and
- Extensor digiti minimi.
2.2nd group
The muscles form an anatomical snuffbox. They are
- Abductor pollicis longus,
- Extensor pollicis brevis, and
- Extensor pollicis longus
Note:
The symbol ” ” at the end of the nerve signifies the branch
The symbol ” ” at the end of the nerve signifies the cutaneous branch
Note:
- The radial nerve is also sensory to the wrist and carpal joints.
- The Dorsum of the hand proximal to 1st web space is an autonomous area for the radial nerve. The autonomous sensory area is part of a dermatome that has no overlap with adjacent nerves.
4. Applied anatomy of the radial nerve
The radial nerve is very commonly damaged in the region of the radial groove. The common causes are:
1. Saturday night palsy: When an intoxicated person falls asleep with his arm hanging over the edge of a chair. The prolonged pressure causes damage to the radial nerve as it is in the radial groove. As a result, in the morning, he finds that he is suffering from a wrist drop.
- It is characterized by flexion of the wrist and flexion of the metacarpophalangeal joint.
- The interphalangeal joints are not affected by wrist drop. They remain straight. This is because of the actions of interossei and lumbrical.
- Testing: This can be detected by testing elbow extension.
- It is purely a transient condition.
2. An interesting term, bridegroom’s paralysis, has been coined for the compression of the radial nerve in the radial grove. It results when the head of the spouse is lying on the arm of the other spouse.
3. The other causes of radial nerve injury include crutch paralysis and fracture of the shaft of the humerus.
4. All these conditions result in weakness and loss of power of extension of the wrist joint. This is called wrist drop.
5. There is minimum sensory loss which is confined to 1st dorsal interosseous. This is because there is an overlap of the nerve supply by the median and ulnar nerves. In addition to wrist drop, there is sensory loss over a narrow strip on the back of the forearm and the lateral side of the dorsum of the hand.
Injury to the superficial branch results in small sensory loss over the root of the thumb.
The integrity of the radial nerve can be confirmed by testing the sensations over the dorsum of the hand proximal to 1st web space.
Surgical approach
- Exposure of radial nerve.
- First, the radial nerve may be exposed from the back by developing an interval between the long and lateral head of the triceps. Here the nerve crosses the upper part of the medial head.
The superficial and deep branches of the radial nerve can be exposed by retracting the brachioradialis and extensor carpi radialis longus.
The deep branch is exposed by incising the deep part of the supinator muscle.
Distribution of radial nerve.
The keyword for the muscles supplied by the radial nerve is BEST.
The letter B represents Brachialis.
The letter E stands for Extensors of the forearm.
The letter S denotes Supinator.
The letter T represents the Triceps.
Applied Anatomy Of Radial Nerve
Applied Anatomy:
Injury to the radial nerve at different levels.
Injury to the radial nerve at various sites and the effects of sensory and motor nerves
Wrist Drop
Wrist Drop Introduction:
It is loss of extension of the wrist due to paralysis of the extensor muscles of the wrist joint.
1. Wrist Drop Nerve Involved
It is produced by the lesion of the radial nerve and/or posterior interosseous branch of the radial nerve.
2. Wrist Drop Causes Of The Injury
In the axilla
- Saturday night palsy, and
- Crutch palsy.
In the middle of the arm
- Fracture of middle 1/3rd of the shaft of humerus, and
- Injection in the radial groove.
In the proximal part of the forearm: Fracture of proximal 1/3rd of radius
3. Wrist Drop Muscles paralysed
1. Extensor carpi radialis brevis
2. Supinator,
3. Muscles forming anatomical snuffbox.
- Abductor pollicis longus
- Extensor pollicis brevis
- Extensor pollicis longus
4. Other muscles
- Extensor indices,
- Extensor digitorum,
- Extensor digiti minimi, and
- Extensor carpi ulnaris.
4. Wrist Drop Clinical manifestations
1. Motor:
The patient is unable to extend the wrist which results in wrist drop.
2. Sensory:
A variable small area of anaesthesia is present over the dorsal surface of the hand and dorsal surface of the roots of the lateral 3½ fingers.
Profunda Brachii Artery
1. Profunda Brachii Artery Origin
It is the largest and deepest (profound-deep) branch of the brachial artery.
2. Profunda Brachii Artery Course and relations
It accompanies the radial nerve in the lower lar space and radial groove. It pierces the lateral intramuscular septum and divides into branches.
3. Profunda Brachii Artery Branches
- Deltoid branch: It ascends between the long and lateral head of the triceps and anastomoses with the descending branch of the posterior circumflex humeral artery.
- Nutrient artery to the humerus.
- The radial collateral artery is one of the terminal branches and represents the continuation of the profunda artery. It ends by anastomosing with the radial recurrent artery.
- The middle collateral artery is the larger terminal branch. It ends by anastomosing with the interosseous recurrent artery.
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