Intact myelinated fibres in biopsies of ventral spinal roots after preganglionic traction injury to the brachial plexus. A proof that Sherrington's 'wrong way afferents" exist in man?

Bell-Magendie's law of separation of spinal function states that afferent a nd efferent fibres join the spinal cord separately in ventral and dorsal sp inal nerve roots. For over 100 years there have been reports that challenge the exclusiveness of this law in mammals; very few studies have referred t o man. We conducted a prospective morphological study in patients with preg anglionic traction injuries of the brachial plexus to address this question . Avulsed ventral and dorsal roots were examined after variable intervals f rom the injury for histological anti ultrastructural evidence for myelinate d afferent fibres entering the cord via the ventral roots. Intact myelinate d fibres were found in all ventral root specimens, but the majority of fibr es in later biopsies are regenerative. A small number of fibres could be de monstrated that are likely to be 'wrong way ventral afferents'. Their numbe r is falsely low due to wallerian degeneration of dorsal and ventral effere nts following the mechanical and ischaemic effects of traction injury. Our findings are the first morphological evidence in human material that Bell-M agendie's law might not entirely be correct and they underline the difficul ties in comparing traumatic with experimental rhizotomy.