Clinical features

The clinical features of radial nerve palsy depend upon the site of the injury.

Lesions in or above the axilla result in paralysis and wasting of all the muscles innervated. Clinically, this is manifest as:

• weakness of forearm extension and flexion - triceps and brachioradialis
• wrist drop and finger drop - paralysis of the extensors of the wrist and digits
• weakness of the long thumb abductor and extensor muscles
• sensory loss on the dorsum of hand and forearm appropriate to the cutaneous distribution - see radial nerve anatomy

Lesions around the humerus often do not affect the triceps and may also spare brachioradialis and extensor carpi radialis longus. The picture more closely resembles posterior interosseous palsy.

Posterior interosseous palsy results from entrapment of the nerve at its point of entry into the supinator muscles. It is often due to a dislocation or fracture of the elbow. Presentation is with weakness of finger extension, and of thumb extension and abduction. There is little or no wrist drop, and usually, no sensory loss.

Investigation of extension of the thumb and fingers must be done carefully since the interossei - ulnar nerve - produce extension of the middle and distal phalanges.