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Concept
Axonotmesis
Summary
Axonotmesis is an injury to the peripheral nerve of one of the extremities of the body. The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact. Motor and sensory functions distal to the point of injury are completely lost over time leading to Wallerian degeneration due to ischemia, or loss of blood supply. Axonotmesis is usually the result of a more severe crush or contusion than neurapraxia.
Axonotmesis mainly follows a stretch injury. These stretch injuries can either dislocate joints or fracture a limb, due to which peripheral nerves are severed. If the sharp pain from the exposed axon of the nerve is not observed, one can identify a nerve injury from abnormal sensations in their limb. A doctor may ask for a nerve conduction velocity (NCV) test to completely diagnose the issue. If diagnosed as nerve injury, electromyography performed after 3 to 4 weeks shows signs of denervations and fibrillations, or irregular connections and contractions of muscles.
There are two kinds of nerve injury classifications:
Endoneurial tube remains intact
Emergence of Wallerian degeneration
Can be detected with Tinel's sign
Endoneurial tube is damaged
Perineurium remains intact
Scarring occurs
Intrafascicular fibrosis occurs due to edema
Perineurium is damaged
Epineurium remains intact
Neuroma could occur
Surgery is required for treatment
A nerve contains sensory fibers, motor fibers, or both. Sensory fibers lesions cause the sensory problems below to the site of injury. Motor fibers injuries may involve lower motor neurons, sympathetic fibers, and or both.
Assessment items include:
Sensory fibers that send sensory information to the central nervous system.
Motor fibers that allow movement of skeletal muscle.
Sympathetic fibers that innervate the skin and blood vessels of the four extremities.
In assessment, sensory-motor defects may be mild, moderate, or severe. Damage to motor fibers results in paralysis of the muscles.
Official source
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