MRCS Part B (OSCE) - Online Resources

The radial nerve originates from the posterior cord of the brachial plexus.

"Roots C5, C6, C7, C8 and T1. "

"

• Enters the posterior compartment of the arm through the triangular interval (lower triangular space) with the profunda brachii artery.
• Descends medial to lateral and lies in the spiral groove of humerus below the lateral head of triceps.
• Gives off branches to triceps before it winds around the spiral groove.
• Emerges from the spiral groove on the lateral aspect of the humerus.
• Pierces the lateral intermuscular septum and lies beneath brachioradialis.
• In the forearm, once the radial nerve passes through the two heads of the supinator muscle, the posterior interosseous nerve (deep nerve) branches from the radial nerve and the radial nerve continues as a sensory nerve (commonly referred to as superficial or cutaneous branch of radial nerve) undercover of brachioradialis.

"

"

The muscles innervated by the radial nerve and its branches are:

• Triceps.
• Anconeus.
• Brachioradialis.
• Extensor carpi radialis longus
• Brachialis (predominantly supplied by the musculocutaneous nerve except for proprioception which is supplied by the radial nerve).
• Sensation over the posterior aspect of the arm and dorsum of the forearm via the posterior cutaneous branch.
• Supinator.
• All extensor muscles of the forearm:

1. Extensor carpi radialis brevis.
2. Extensor digitorum communis.
3. Abductor pollicis longus.
4. Extensor indices.
5. Extensor pollicis longus.
6. Extensor pollicis brevis.
7. Extensor digiti minimi
8. Extensor carpi ulnaris.

"

"

• Test extension of triceps.
• Test brachioradialis (flex the elbow in mid-prone position against resistance).
• Test supinator (with the elbow extended test supination against resistance).
• Test wrist extension (ask patient to extend the wrist against resistance).
• Test finger extension.

"

"Extensor pollicis longus (EPL) tendon is tested by the retropulsion test. With the patient’s hand palm down on a flat surface, ask them to lift their thumb up towards the ceiling against resistance and also palpate the integrity of the EPL tendon in this position. "

"

• In the axilla: Such as following surgery to the axilla, direct trauma and ill-fitting crutches.
• At the level of the mid-humerus: The nerve vulnerable to injury at the level of the spiral groove following mid-shaft fractures of the humerus.
• At and below the level of the elbow: The nerve is at risk at this level following elbow dislocations, Monteggia fractures, ganglions, iatrogenic injuries and trauma.
• Supinator tunnel (‘Arcade of Frohse’): The deep branch of the radial nerve is most susceptible at this level.

"

"Injury to the radial nerve below the spiral groove presents with wrist drop (inability to extend the muscles of the forearm and hand) but no loss of elbow extension as branches to triceps remain intact proximal to this level. Loss of elbow extension (triceps) and wrist drop indicates a higher lesion above the spiral groove. "

"Injury to the posterior interosseous (deep) branch presents with inability to extend the metacarpophalangeal joints. Injury to the PIN does not result in complete wrist drop as the extensor carpi radialis longus remains receives its innervation directly from the radial nerve. The patient will be able to extend the wrist weakly albeit with radial deviation. "

"The superficial radial nerve travels underneath the brachioradialis in the proximal forearm. As it descends distally, it passes over the aponeurotic border of the brachioradialis before dividing into several sensory branches supplying the radial aspect of the dorsum of the hand (radial 3½ digits to the level of the proximal phalanges; autonomous zone: skin overlying the 1st dorsal webspace). "

Motor deficits following radial nerve injury include decreased wrist and finger extension and, decreased thumb abduction and extension. Common tendon transfers to address these deficits include:
 Pronator teres to extensor carpi radialis brevis tendon.
 Flexor carpi ulnaris to extensor digitorum communis tendon.
 Palmaris longus to extensor pollicis longus tendon.
 Superficialis transfers (FDS of middle finger to EDC; FDS of the ring finger to EIP and EPL; FCR to APL and EPB).