Radial Nerve Palsy Test

Radial nerve palsy test is done by these special tests:

1. Wrist drop test
2. Thumb Extension Test
3. Supination Test.

See Also: Extensor compartments of the wrist

Wrist Drop Test

The patient is asked to extend his or her wrist with the elbow flexed 90°.

In radial nerve palsy affecting the wrist extensors, the patient will be unable to extend the wrist. The hand will hang down in a deformity commonly known as a “wrist drop“.

In a second stage of the test, the patient is asked to abduct the thumb. In radial nerve palsy, the patient will be unable to abduct the thumb because of the paralysis of the abductor pollicis longus muscle and, to a lesser extent, the extensor pollicis brevis muscle.

Radial nerve lesions usually occur secondary to humeral shaft fractures. Another cause is sleep palsy (“Saturday night palsy” or “park-bench palsy”) which has a better prognosis.

Thumb Extension Test

The patient is seated. The examiner grasps the patient’s wrist with one hand and presses the thumb into adduction with the other hand. Then the patient is asked to extend or abduct both the metacarpophalangeal and interphalangeal joints of the thumb.

Thumb Extension Test requires an intact radial nerve. Where this nerve is damaged, thumb extension will be weakened or impossible as a result of paralysis of the extensor pollicis longus and brevis.

In patients with degenerative joint disease or rheumatoid arthritis in the joints of the thumb, this test generally produces pain in addition to demonstrating weakness. Simple nerve palsy without degenerative changes will not produce any joint symptoms.

Supination Test

Supination Test Evaluates a compression neuropathy of the deep branch of the radial nerve.

The patient is seated, holding the elbow slightly flexed and the forearm pronated. The elbow is held alongside the trunk to minimize motion in the shoulder. The patient is then asked to supinate his or her forearm , at first normally and then against the examiner’s resistance.

Weakness or loss of supination of the forearm is a sign of paresis of the supinator muscle, which is supplied by the deep branch of the radial nerve.

Care should be taken not to flex the elbow too much during this test, because the biceps also participates in supination as elbow flexion increases. Despite the fact that both muscles are naturally involved in supination, increasing elbow flexion would lead to false-negative test results, because the biceps has more responsibility for supination when the elbow is significantly flexed, whereas the supinator has far greater influence on supination when the elbow is extended.

A supinator compartment syndrome occurs from hardening of the soft tissue, as a result of trauma such as dislocation of the radial head or Monteggia fracture, and rarely from an intramuscular injection.

Radial Nerve Anatomy

The radial nerve is the largest branch of the brachial plexus.

The radial nerve crosses the elbow immediately anterior to the radial head, just beneath the heads of the extensor origin of the extensor carpi radialis brevis (ECRB), and then divides, with the deep branch running through the body of the supinator muscle to the posterior aspect of the forearm.

The radial nerve in the arm supplies the triceps, the anconeus, and the upper portion of the extensor supinator group of forearm muscles.

In the forearm, the posterior interosseous nerve innervates all of the muscles of the six extensor compartments of the wrist, with the exception of the ECRB and extensor carpi radialis longus (ECRL).

The skin areas supplied by the radial nerve include:

1. the posterior cutaneous (brachial) nerve of the arm, to the posterior (dorsal) aspect of the arm;
2. the posterior cutaneous (antebrachial) nerve of the forearm, to the posterior (dorsal) surface of the forearm;
3. the superficial radial nerve, to the posterior (dorsal) aspect of the radial half of the hand.
4. The isolated area of supply is a small patch of skin over the posterior aspect of the first interosseous space.

See Also: Brachial Plexus Anatomy

References

1. Han BR, Cho YJ, Yang JS, Kang SH, Choi HJ. Clinical features of wrist drop caused by compressive radial neuropathy and its anatomical considerations. J Korean Neurosurg Soc. 2014 Mar;55(3):148-51. doi: 10.3340/jkns.2014.55.3.148. Epub 2014 Mar 31. PMID: 24851150; PMCID: PMC4024814.
2. Gragossian A, Varacallo M. Radial Nerve Injury. [Updated 2021 Aug 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537304/
3. The radial nerve (C6–8, T1). (Reproduced, with permission, from Waxman SG: Clinical Neuroanatomy, 26th ed,-Hill, 2010).
4. Clinical Tests for the Musculoskeletal System 3rd Edition.
5. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.