69R. Birch, Peripheral Nerve Injuries: A Clinical Guide, DOI 10.1007/978-1-4471-4613-1_2, © Springer-Verlag London 2013


The conducting element of the nerve fi bre, the axon, responds to focal injury in a number of ways. There are two essential lesions. In the fi rst, the axon is intact but conduction at the level of lesion is blocked. This is conduction block ( CB). There is no Wallerian degeneration; this is the non degenerative lesion. Recovery will be complete if the cause is removed. In the second, the axon is transected. Wallerian degeneration ensues; this is the degenerative lesion. There are two types of degen-erative lesion. In the fi rst, the basal lamina of the Schwann cell envelope is intact and the axon can regenerate in an orderly fashion into the distal Schwann cell tube. In the second type the basal lamina has been interrupted and spontaneous regeneration will be imperfect, disorderly and may not occur at all. Seddon [ 32] introduced the terms neurapraxia for CB, axonotmesis for the degenerative lesion of favourable prognosis because of the intact basal lamina, and neurotmesis for the degenerative lesion of unfavourable prognosis because the basal lamina has been interrupted. In clinical practice neurotmesis usually represents severance not only of the axon and its Schwann cell envelope but also of the perineurium and the epineurium. The difference between CB and the unfavourable degenerative lesion, neurot-mesis, is exempli fi ed by two clinical situations which are common enough. Case report: Pure CB: A fi t 23 year old woman fell deeply asleep lying on her left side for about 2 h and awoke with a complete left sided radial palsy. She had no pain, there was no Tinel sign and there was some preservation of cutaneous sensibil-ity within the distribution of the nerve. She was fi tted with a dynamic extension splint and at 6 weeks the fi rst evidence of recovery into the extensor muscles of the wrist was apparent. Neurophysiological investigations were performed 9 weeks later which revealed normal conduction and a normal recruitment to a full pattern of motor units of normal appearance. Her recovery was complete by 12 weeks from the incident

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