PERIPHERAL NERVE INJURY;CLASSIFICATION;ASSESSMENT OF PERIPHERAL NERVE INJURY

 PERIPHERAL NERVE INJURY

• A single peripheral nerve is composed of many nerve fibers or axons which are arranged in groups called fascicles. 

• The majority of nerve volume is composed of connective tissue and not axons although the amount of connective tissue differs from nerve to nerve and at different distances.

• These connective tissue consists of the endoneurium which covers a single axon.

• The perineurium which covers the entire fascicle. 

• The interfascicular epineurium that separates the fascicle from each other and then the outermost covering of the peripheral nerve is called the epineurium.

• The connective tissue layer helps in protecting and providing nutrition to the enclosed nerve fibers. 

• External to the epineurium is a transparent thin layer of mesoneurium which serves to secure nerve to adjacent structures such as tendons, vessels, muscles and fascial planes. 

• The neural structure is comprised of axons and their accompanying Schwann cells.

• Even the neural fibers and their Schwann cells are surrounded by collagen fibrils to bring about some degree of condensation.

• Schwann cells are placed along the longitudinal extent of the axon.

•  In between the Schwann cells there is the node of Ranvier which causes saltatory conduction of impulse.

•  The nerve fibers are of two types, the large fibers and the smaller fibers. 

• The larger fibers are more myelinated and concerned with muscles, touch, pressure and some pain. 

• The smaller diameter fiber is concerned with autonomic and most pain.

CLASSIFICATION

• There are two classifications of PNI which were put forth by Seddom and Sutherland. 

The Seddom classification of PNI is neurapraxia,axonotmesis and neurotmesis.

Sutherland classification

ASSESSMENT OF PERIPHERAL NERVE INJURY

• After collecting the demographic information, chief complaint, history from the patient, one should proceed with the evaluation in the following manner:

Observation

•  Attitude of the part (presence of wrist drop, claw hand etc) wasting, trophic changes in the skin (indicates either prolonged inactivity or involvement of fiber in the peripheral nerve regulating autonomic function), pilomotor response and edema.

Examination Sensory

• The therapist may evaluate the sensory function along the cutaneous distribution of that peripheral nerve. Thus, interpretation of the sensory dysfunctions is also with respect to the distribution of the peripheral nerve and not dermatomically.

Reflexes

• The deep and superficial reflexes should be checked only if the particular nerve or its muscular supply are involved in the reflex arc for any specific reflex. 

• Thus deep tendon jerks should be tested for musculocutaneous nerve involvement (biceps is supplied by musculocutaneous nerve) but can be avoided for ulnar nerve injury.

Tone

• Quick passive movement is done to examine tone. In PNI the patient has hypotonicity or atonicity.

MMT

• Individual MMT is to be done; the therapist should also have adequate knowledge about the types of trick movements to be noticed in patients with weakness or paralysis because otherwise the grading may be completely wrong.

Sweat Function Test

• This is one of the ways to check out for involvement of autonomous function in peripheral nerve injury. 

• There are four types of sweat function tests that may be used commonly. 

The Q-Sweat (Quantitative Sweat Measurement System) quantifies human skin sweat output. 

• This patented device precisely measures sweat rate and volume via a closed chamber that is affixed to the skin and displays the data in real time in an easy-to-read, Windows-based graphical user interface.

Ninhydrin Test

• Ninhydrin powder is sprayed over the skin. When this powder comes in contact with the skin it changes it’s color. If the color does not change then it means the area does not have sweat function. (To stimulate sweating the patient may be given an atmosphere that will stimulate sweat reaction).

Chinizarin Start Test

• Prepare a dry powder mixture of quinizarin (Chinizarin) sodium 35g, sodium carbonate 30 g, and rice starch 30 g. 

• Dust the reddish-grey powder over skin to be tested and place under a heat cradle for 15 to 45 minutes. 

• The powder will change its color when it comes in contact with sweat.

Galvanic Skin Resistance Test

• Sweating will decrease the skin resistance and will facilitate flow of current through skin, thus if the resistance offered by skin surface is more than the other areas in the body then it can be interpreted that there is sweat dysfunction which is contributing towards the increased skin resistance.

Investigations

• SDC should be done periodically. It may show a normal response till wallerian degeneration is complete but later will show signs of denervation. 

• EMG should be done and will show a typical neurogenic presentation. 

• NCV will show decreased conduction velocity across the lesion but proper interpretation is necessary to differentiate between neurapraxia, axonotmesis and neurotmesis.

• F latency can be done to confirm proximal lesion to the motor axon.