The patient is asked to hold his fingers fully adducted with metacarpophalangeal joint (MCP), proximal interphalangeal joints (PIP), and distal interphalangeal joints (DIP) joints fully extended.
What does a positive Wartenberg Sign mean?
Wartenberg Sign is considered Positive if small finger drifts away into abduction from other fingers, indicating an injury to the ulnar nerve.
This due to the unopposed action of extensor digiti minimi that is innervated by the radial nerve.
This sign could be confused with Wartenberg Syndrome or Cheralgia Paresthetica, in which the Superficial radial nerve becomes compressed as it comes superficial at brachioradialis and ECRB interval in distal forearm causing sensory disturbance, it’s characterized by pain and tenderness 1 to 2 cm proximal to the radial styloid, and radicular pain distally along the course of the superficial radial nerve elicited by percussion.
Ulnar nerve (C8,T1) is a branch of the medial cord of brachial plexus.
It gives motor branches to:
Flexor carpi ulnaris muscle (FCU).
Ulnar half of flexor digitorum profundus muscle (FDP).
Abductor digiti minimi muscle.
Opponens digiti minimi muscle.
Flexor digiti minimi muscle.
3rd and 4th lumbricals muscles.
Adductor pollicis muscle.
And sometimes deep head of flexor pollicis brevis muscle.
Sensory distribution is over ulnar 1 ½ fingers and ulnar aspect of hand.
Kilgus M, Burg D, Loss M, Weishaupt D, Meyer VE. Das Wartenberg-Zeichen des Nervus ulnaris. Ein Beitrag zur Pathophysiologie und Differenzialdiagnose1 [Wartenberg’s Sign of Ulnar Nerve Lesion. A Contribution to Pathophysiology and to the Differential Diagnosis]. Handchir Mikrochir Plast Chir. 2003 Jul;35(4):251-8. German. doi: 10.1055/s-2003-42134. PMID: 12968223.