A nerve injury can result in weakness or paralysis of a muscle or in numbness of an area of skin. In some people,
it also causes pain. To understand nerve injury and recovery, it is important to understand the different types of
nerve injury. The type of nerve injury will determine the type of treatment.
Nerve Injury Classification System
Nerve injuries are classified as follows:
- A first-degree injury, or neurapraxia, will recover within days after the injury, or it may take up
to three months. The recovery will be complete with no lasting muscle or sensory problems.
- A second-degree injury, or axonotmesis, also will recover completely; however, the recovery will
take much longer than with a first-degree injury.
- A third-degree injury also will recover slowly; in addition, only partial recovery will occur.
- A fourth-degree injury occurs when there is dense scar tissue within the nerve, completely blocking
any recovery. Surgery is required for recovery.
- A fifth-degree injury involves complete separation of a nerve, such as a cut nerve. Surgery is
required for recovery.
- A sixth-degree injury is a combination of other types of nerve injury. Recovery and treatment
will vary depending on which types of nerve injury are present.
Diagrammatic Representation And Cross Section
Text and illustrations from Surgery of the Peripheral Nerve
by Mackinnon and Dellon,
reprinted with permission of Thieme Medical Publishers, Inc.
- a. Diagrammatic representation of the cross section of a normal peripheral nerve demonstrating the
connective tissue and nerve tissue components.
- b. The cross section of the peripheral nerve demonstrates a
mixed, or sixth degree, injury pattern. This fascicle (bundle of nerve fibers) at 11 oâ€™clock is normal.
Moving counterclockwise, the adjacent fascicle demonstrates a first degree injury (neurapraxia) with
segmental demyelination (loss of the myelin that covers many nerve fibers).
The next fascicle demonstrates a second degree injury (axonotmesis). This injury involves both
the axon and the myelin. The endoneurial tissue (delicate connective tissue network that holds
together the individual fibers of a nerve trunk) is not damaged.
The central two fascicles demonstrate a third degree injury, with injury to the axon, myelin and
endoneurium. The perineurium (sheath of connective tissue that surrounds a bundle of nerve fibers)
is intact and normal.
The fascicles demonstrate at 12 and 1 oâ€™clock a fourth degree injury with marked scarring across
the nerve, with only the epineurium being intact.
In a fifth degree injury pattern, the nerve is not in-continuity but is transected. The surgeon will
separate the fourth and fifth degree injury patterns, which will require reconstruction from the normal
fascicles and the fascicles demonstrating first, second and third degree injury patterns. These latter
patterns of injury require, at most, neurolysis (destruction of nervous tissue).
Nerve Recovery and Regeneration
After nerve injury, the nerve will try to repair itself by sprouting regenerating nerve units. These regenerating
units will then try to grow down the nerve to reinnervate (restore nervous function to) muscle or skin. If they make
a correct connection â€” motor nerve to muscle or sensory nerve to skin â€” then recovery of muscle function and skin
sensation will occur. However, if the regenerating nerve fibers do not make a correct connection, then no recovery will occur.
Peripheral Nerve Surgery
If surgery is necessary, there are several types of surgery that may be recommended.
For nerve regeneration, the regenerating nerve fibers need the guidance of the nerve for direction to the muscle
or sensory unit. If the nerve has been cut, a nerve repair is used to sew the two ends of a nerve together. This
usually is possible when the nerve has been cut sharply. However, in cases with more extensive damage, it may not
be possible to sew the two ends of the nerve directly together once the damaged nerve has been trimmed away.
In these cases, a nerve graft
is used. A small piece of donor nerve is used to bridge the gap
between the two nerve ends, and the nerve will regenerate across this â€śbridgeâ€ť to provide recovery. The donor
nerve is taken from other areas of your body using small, noncritical sensory nerves.
In some cases in which sensory or muscle recovery is not anticipated for a very long time, a nerve transfer
may be used. Nerve transfers use functioning nerves that are close to the target muscle or sensory area, and the nerves are
transferred to the injured nerve.
A neurolysis (or nerve decompression) refers to the removal of scar or compressive structures (including
fascia or tendonous edges of muscles) from the nerve and may be undertaken if external impediments (or
tight "tunnels") are pinching the nerve, limiting the ability of the regenerating unit to pass through
on its way to its target.
Other techniques to restore muscle function, tendon transfers
and free functional muscle transplants
also are covered on our web site.
Patient information on nerve injury