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M01.03.028 Radial Nerve
The radial nerve is a major peripheral nerve of the upper limb, integral to motor and sensory functions. This guide explores its anatomical course, motor and sensory functions, and the clinical implications of its damage.
Overview of the Radial Nerve
| Feature | Details |
|---|---|
| Nerve Roots | C5–T1 |
| Motor Functions | Innervates the triceps brachii and extensor muscles in the forearm. |
| Sensory Functions | Provides sensation to the posterior forearm, lateral dorsum of the hand, and dorsal surface of the lateral 3.5 digits. |
Anatomical Course
The radial nerve originates as the terminal continuation of the posterior cord of the brachial plexus (C5-T1).
Key Steps in its Course:
- Axilla:
- Positioned posteriorly to the axillary artery.
- Supplies branches to the long and lateral heads of the triceps brachii.
- Exits via the triangular interval.
- Arm:
- Travels within the radial groove of the humerus alongside the deep brachial artery.
- Supplies the medial head of the triceps brachii.
- Forearm:
- Passes anterior to the lateral epicondyle of the humerus via the cubital fossa.
- Divides into two terminal branches:
- Deep Branch (Motor): Innervates posterior forearm muscles.
- Superficial Branch (Sensory): Provides sensation to the dorsal hand and lateral digits.
Motor Functions
The radial nerve controls muscles primarily responsible for extension and supination.
Innervated Muscles:
| Region | Muscles |
|---|---|
| Arm | Triceps brachii (long, lateral, medial heads) |
| Forearm (posterior) | Extensor carpi radialis longus, brachioradialis (via main branch); other extensors via deep branch. |
Note: After penetrating the supinator, the deep branch becomes the posterior interosseous nerve.
Sensory Functions
The radial nerve provides sensory innervation through four branches:
| Branch | Innervation |
|---|---|
| Lower lateral cutaneous nerve | Lateral aspect of the arm (below deltoid insertion). |
| Posterior cutaneous nerve of arm | Posterior surface of the arm. |
| Posterior cutaneous nerve of forearm | Midline of the posterior forearm. |
| Superficial branch | Dorsal surface of lateral 3.5 digits and associated dorsum of the hand. |
Clinical Relevance: Radial Nerve Injury
1. Injury in the Axilla
- Mechanism: Dislocation of the shoulder, proximal humerus fracture, or improper crutch use.
- Motor Deficits:
- Loss of extension at the elbow, wrist, and fingers (wrist-drop).
- Sensory Deficits:
- Loss of sensation over lateral and posterior arm, posterior forearm, and dorsal lateral digits.
2. Injury in the Radial Groove
- Mechanism: Humeral shaft fracture.
- Motor Deficits:
- Weakness in triceps brachii (some fibers unaffected).
- Wrist-drop due to posterior forearm muscle paralysis.
- Sensory Deficits:
- Loss of sensation in the dorsum of lateral digits.
3. Injury in the Forearm
| Superficial Branch | Deep Branch |
|---|---|
| Mechanism: Laceration or stab wound. | Fracture of radial head or dislocation of radius. |
| Motor: None. | Most posterior forearm muscles affected. |
| Sensory: Lateral 3.5 digits dorsum. | None. |
Points to Remember
- The radial nerve originates from C5–T1 and is a continuation of the posterior cord of the brachial plexus.
- It provides motor innervation to extensors of the arm and forearm.
- It supplies sensation to the posterior arm, forearm, and dorsal lateral hand.
- Common clinical presentations of injury include wrist-drop and sensory loss on the hand dorsum.
- The location of injury determines the extent of motor and sensory impairment.
Bibliography
- TeachMeSeries Ltd (2024). Radial Nerve Anatomy.
- Shoulderdoc.co.uk [CC BY-SA 2.0].