A new type of brachial plexus lesion has been defined to be added to the classical types, i.e. the upper (Duchenne Erb), the lower (Dejerine Klumpke) and the total type. This new type is the intermediate palsy. The lesion is a partial involvement of the plexus, the predominant lesion of which involves C7 with a variable involvement of the upper or lower plexus. By observations during operation, and in cadavers, three different mechanisms are considered responsible for the three different types of lesion. A trauma with downwards traction principally involves the upper plexus. Trauma in abduction first involves the lower plexus while a traumatic force acting from an anterior to a posterior direction involves firstly and predominantly the C7 spinal nerve which is in an anterior position and less oblique than the other roots. Avulsion from the cord or rupture are possible. 33 cases have been observed.
