Axonotmesis is an injury to the peripheral nerve of one of the extremities of the body. The

axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action ...

s and their

myelin sheath Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be l ...

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 Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...

, 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 Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

performed after 3 to 4 weeks shows signs of denervations and fibrillations, or irregular connections and contractions of muscles.

Injury classification

There are two kinds of nerve injury classifications:

Sunderland's Stage II classification

Endoneurial The endoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber in the peripheral nervous system. Its co ...

tube remains intact * Emergence of Wallerian degeneration * Can be detected with

Tinel's sign Tinel's sign (also Hoffmann-Tinel sign) is a way to detect irritated nerves. It is performed by lightly tapping ( percussing) over the nerve to elicit a sensation of tingling or "pins and needles" in the distribution of the nerve. Percussion is usu ...

Sunderland's Stage III classification

* Endoneurial tube is damaged * Perineurium remains intact * Scarring occurs * Intrafascicular

fibrosis Fibrosis, also known as fibrotic scarring, is a pathological wound healing in which connective tissue replaces normal parenchymal tissue to the extent that it goes unchecked, leading to considerable tissue remodelling and the formation of permane ...

occurs due to

edema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...

Sunderland's Stage IV classification

* Perineurium is damaged * Epineurium remains intact *

Neuroma A neuroma (; plural: neuromata or neuromas) is a growth or tumor of nerve tissue. Neuromas tend to be benign (i.e. not cancerous); many nerve tumors, including those that are commonly malignant, are nowadays referred to by other terms. Neur ...

could occur * Surgery is required for treatment

Assessment

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...

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 The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

. * Motor fibers that allow movement of

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of m ...

. * 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.

Nervous plexus A nerve plexus is a plexus (branching network) of intersecting nerves. A nerve plexus is composed of afferent and efferent fibers that arise from the merging of the anterior rami of spinal nerves and blood vessels. There are five spinal nerve ple ...

injuries create more signs and symptoms from sensory-motor problems (such as brachial plexus injuries). In these cases, the prognosis depends on the amount of damage and the degree of functional impairment.

EMG and NCV findings

Changes in EMG

Electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

(EMG) is a medical test performed to evaluate and record the electrical activity (electromyogram) produced by skeletal muscles using an instrument called electromyograph. In axonotmesis, EMG changes (2 to 3 weeks after injury) in the denervated muscles include: # Fibrillation potentials (FP) # Positive sharp waves

Changes in NCV (nerve conduction velocity)

EMG test is often performed together with another test called nerve conduction study, which measures the conducting function of nerves. NCV study shows loss of nerve conduction in the

distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

segment (3 to 4 days after injury). According to NCV study, in axonotmesis there is an absence of distal sensory-motor responses.

Treatment

Schwann cell Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory ...

s provide the nerve with protection through the production of

Nerve Growth Factors Nerve growth factor (NGF) is a neurotrophic factor and neuropeptide primarily involved in the regulation of growth, maintenance, proliferation, and survival of certain target neurons. It is perhaps the prototypical growth factor, in that it was on ...

, and because these cells are intact this kind of nerve injury can be cured and normal feeling and sensations can be restored. Surgery can be done in order to help the nerve heal. The surgery will help with nerve regeneration, providing guidance to the nerve sprouts on where to attach on the

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position ...

side of the injury. Damaged nerve axons can reattach themselves after surgery. Treatment of axonotmesis also consists of: *

Physical therapy Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patie ...

or Occupational Therapy. Physical or Occupational therapy aims include: ** Pain relief ** Maintain range of motion ** Reducing

muscular atrophy Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Muscle atrophy leads to muscle weaknes ...

** Patient education * Use of assistive devices (Orthotic needs)

Prognosis

The prognosis is usually good in terms of recovery. Rate of recovery depends on the distance from the site of injury, and

regeneration Regeneration may refer to: Science and technology * Regeneration (biology), the ability to recreate lost or damaged cells, tissues, organs and limbs * Regeneration (ecology), the ability of ecosystems to regenerate biomass, using photosynthesis ...

can go up to 1 inch per month. Complete recovery can take anywhere from 6 months to a year.Otto D. Payton & Richard P. Di Fabio et al. Manual of physical therapy. Churchill Livingstone Inc. Page 24.

References

{{DEFAULTSORT:Nerve Injury *