The Ulnar Nerve

Fig 1: Claw Hand

The ulnar nerve (usually) supplies sensation to the skin of the fifth and the ulnar side of the fourth finger, front and back. There is sympathetic interruption, with absence of sweating in the affected area. The thenar muscles are supplied by the median nerve and are therefore spared. Although the fourth and fifth digits are held in the clawed position when the nerve is injured at the wrist, a high lesion paralyses the long flexors to these two fingers and results in the loss of this sign. A test for paralysis of the palmar interossei, supplied by the ulnar nerve, is the inability to adduct the fingers and thus to be unable to grip a sheet of paper between them. 

Fig 2: Entrapment of Ulnar Nerve

Fig 3: Cutaneous Innervation of Right Upper Limb

Further Reading