Mechanical injury of peripheral nerves. Fine structure and dysfunction.

In summary we have examined the morphology of the normal peripheral nerve, presented the types of mechanical nerve injury and associated histopathology, and discussed possible mechanisms responsible for symptoms of pain, paresthesiae, and weakness associated with these lesions. Neurapraxia consists of intussusception of axon and myelin through the nodes of Ranvier resulting in prolonged nerve conduction block. Axonotmesis and neurotmesis describe more severe disruptions of nerve fiber architecture, are difficult to distinguish electrophysiologically, and have poorer prognoses for functional regenerative repair. Chronic entrapment lesions consist of telescoping myelin internodes and tapering of the sheaths with bulbous polarization of internodes away from the site of injury. Both acute and chronic lesions chiefly involve large myelinated fibers and both may create neuralgia, although the mechanism by which this occurs is poorly understood. Presently, increasing evidence suggests ectopic impulse generators and ephaptic transmission may be responsible for sensorimotor phenomena in these lesions.