[Reinnervation in obstetrical brachial plexus paralysis].

Post-paralytic associated movements ("co-contractions") in 16 cases with obstetrical brachial plexus palsy (OPP) were studied by a neurographic method. This consisted of stimulating a nerve and searching for heterogeneous motor axon reflexes (HAR) in the muscles of the upper limb and shoulder. HAR can be elicited when branches of a single axon reach two different muscles, even very distant from each other. The anatomy of the plexus and the fact that regenerating axons maintain direction determine the frequency with which two muscles are connected. Most HAR are recorded in muscles innervated by the same nerve or roots. More than 800 of them were recorded, mainly in muscles with associated movements. Motor fibers were also detected in sensory nerves. The synkinesis can be explained by a complexe misdirection ("fausse route complexe"): the branches of a single axon reach several muscles. There is no need to propose a simple misdirection ("fausse route"), implying that an axon simply changes direction to innervate another muscle, nor to call upon modifications of the central motor patterns. The proposed mechanisms of associated movements in the OPP explains the impossibility of suppressing them by reeducation.