Correction of abduction. Deformity of the small finger caused by avulsion of the insertion of the third volar interosseous muscle.

Wartenberg described the clinical sign of the abducted extended small finger that can result from ulnar nerve palsy. When this sign occurs in ulnar nerve palsy, it is a result of imbalance created by paralysis of the third volar interosseous muscle allowing the extensor digiti minimi to abduct the small finger as the finger is extended. If the third volar interosseous muscle is traumatically avulsed at its insertion and the ulnar nerve is intact, the abductor digiti minimi manus is an additional deforming force.