[Ulnar clasp failure or again "the nail file sign", a little known sign of disorders of the ulnar nerve].

Besides the well known signs of the ulnar palsy, there is a new sign, unknown till now: the "failing ulnar hook". It could be named the "nail file sign", because it was discovered from a woman who could not file the nail of her little finger. Practically, the patient is asked, in a first time, to roll his little and ring fingers around the index of the same hand of the examinator. As the patient is resisting, the other index of the examinator tries to extend these two fingers. If they cannot resist, there is an ulnar palsy at an upper level. The explanation is that the flexor profundus of the ring and the little fingers are commanded by the ulnar nerf, whereas those of the index and the middle finger are by the median nerve. So, when this sign is present, the block is located from the elbow to the brachial plexus. When it is absent, whereas other signs of ulnar palsy are present, it evoques a lower palsy. This sign is of great interest because it confirms the diagnosis of ulnar palsy and allows the localization of the block. It is very useful to search it in every neurologic examination of the hand. In a carpal tunnel syndrome, it allows to eliminate or not an ulnar participation without using of electrical tests.