[N. interosseous anterior syndrome. Study in 4 cases of our own and in 49 cases from the literature (author's transl)].

The anterior interosseous nerve branches off from the median nerve distal of the pronator radii teres. It lies on the interosseous membrane, always innervates the flexor pollicis longus, usually the portion of the deep flexor belonging to the second, sometimes also the portion belonging to the third finger, then runs to the pronator quandratus. In 4 cases of our own and in 49 cases from the literature we could show that an isolated lesion of the motor division of the median nerve has been seen after fractures and in connection with dull traumas, unusual activities, pressure and medical procedures. A mechanical origin can be assumed also in the so-called "spontaneous" cases of paresis without any indication of exogenous influence. It is described twice as often on the right as on the left side and in 15 of 17 cases of operative revision fascial bands, adhesions, and similar compressions were found. Frequently, the only sign of the syndrome is paresis of the flexor pollicis longus. The diagnosis becomes clearer, when the flexor digitorum profundus is also affected, since the extension of the first two or three end phalanges during flexion of all fingers constitutes a characteristic clinical feature. Occasionally, pain is present on the outside of the forearm, and this can lead to differential diagnostic reflections. In spite of the convincing operative findings we find that the experience to date is not sufficient to give a general recommendation for operative treatment. The prognosis is favorable, apparently even without operative revision; in some cases, however, as in one of our patients, the paresis does not improve until the second year after onset.