[Misinterpretation of nerve damage to the hand and forearm due to variations in the motor innervation].

A 21-year-old man served his ulnar nerve at the level of the left elbow. After nerve suturing only a slight loss of strength in two ulnar intrinsic hand muscles was found. Electromyographic examination revealed the crossing of some motor nerve fibres in the forearm from the median nerve to the ulnar nerve, innervating most of the first dorsal interosseous and the abductor digiti minimi muscle. One and a half years later there was still a loss of strength in the other ulnar muscles and a reduced sensitivity of the ulnar area, without a loss of function. Variations in the motor nerve supply of the hand, in particular connections between the median nerve and ulnar nerve in the forearm and hand are common. A complete transection of the ulnar nerve without complete paralysis of the ulnar intrinsic hand muscles can occur. If these variations are not considered, such a transection can be overlooked.