Nerve Lacerations of the Hand

One of the common problems that we treat our lacerations to the hand which may produce lacerations two major nerves.  There are 3 major nerves in the hand: And the radial nerve, the ulnar nerve and median nerve.  At the level of the hands the radial nerve is purely a sensory nerve and supplies sensation to the back or dorsum of the thumb index finger and hand.  The median nerve is a mixed nerve, supplying sensation to the palm side of the thumb, index finger, little finger and half of the ring finger.  It also supplies motor power to the thenar muscles, or muscles of the thumb.  The ulnar nerve is also a mixed nerve, supplying sensation to the palm and dorsum of the small finger and half of the ring finger. the ulnar nerve also supplies motor power to the muscles of the little finger(hypothenar muscles) and the small intrinsic muscles in the hand.  Figure 1 displays the areas of sensation supplied by each nerve.

The symptoms of a nerve laceration are highly variable. there may be loss of sensation or numbness-total or partial.  There may be nerve irritability with hypersensitivity to touch or tingling over the distribution of the nerve.  There may be a partial laceration of the nerve which heals, producing a painful nerve scar or neuroma, creating a painful sensitive area.  Motor or muscle weakness may also result-either complete or partial.  There may be wasting or atrophy of the affected muscles.  This may result in weakness of grip. chronic weakness of certain muscles may result in an imbalance of muscle forces and produced a chronic deformity of the fingers such as the claw finger deformity which can result from the intrinsic weakness seen with an ulnar nerve laceration.

After nerve laceration the distal portion (end towards the fingers) begins to degenerate into process called Wallerian  degeneration. the nerve ends may retract from each other encases up a complete laceration and scar tissue forms at both ends.  In motor nerves the motor endplate, the attachment of the nerve to the muscle, may degenerate after a period of time.  All of these factors work against complete return of nerve function after repair.  The nature of the laceration is also important.  Dirty, jagged, ripping injuries such as chainsaw laceration damage a far bigger segment of the nerve then a clean sharp laceration from glass or a sharp knife.  A tearing or evulsion injury in which a segment of nerve is torn, damages a far bigger section then a simple laceration.  The condition of the tissue around the nerve(nerve bed) and any contamination of the area also affects nerve healing.  Finally the patient's age and overall health are important.  Several studies have shown that nerve repair results over the age of 50 do not compare to nerve repairs of younger adults.  Smoking and nicotine impair microcirculation which affects the results of nerve repair as do malnutrition and alcoholism.

Treatment of nerve lacerations in the hand requires a detailed complete assessment of nerve function and hand function. Complete evaluation of sensation  in cases of partial sensation loss may require sensory mapping with two-point discrimination(a tool to determine the amount of sensation that remains) in order to determine whether protective sensation is still present.  Electrodiagnostic studies they be required in chronic cases to determine exactly which muscles are affected encases a partial nerve laceration. these and other studies as well as a very detailed hand examination help to provide a complete picture of the functional loss caused by the hand nerve laceration. the level of injury is also important.  Lacerations that injure tiny small nerves and lacerations in mixed nerves or with both sensory and motor nerve branches are more difficult. This assessment is coupled with the decision on how much functional loss can be well tolerated in order to create a plan to restore function.  For example, numbness can sometimes be tolerated on the inner aspect of several fingers.  It usually cannot be tolerated on the thumb or outer aspect of the index and little finger due to risk of burns or injury to those fingers.  numbness is better tolerated than numbness and pain and hypersensitivity.  Partial weakness, motor loss or lack of coordination are better tolerated and some patient's than others(pianist, surgeon, artist).

Early treatment of lacerations easily consistent of cleaning or debris the surrounding area of laceration, repairing any other structures that were damaged and then repairing the nerves directly with microsurgical techniques.  This is either usually accomplished immediately after injury or approximately 2 weeks later.  Often the wounds have been cleaned and the skin repaired by the emergency room. The results in such cases are approximately the same. In this surgery, and operating microscope or loupe magnification is used to trim the nerve ends carefully and repair the nerve with several sutures that are smaller than a human hair.  If a large segment of nerve has been damaged and needs to be resected or is missing, a nerve graft(section of matching nerve taken from another donor area) may be used to bridge the gap between the nerve ends.  A newer technique is using a neural tube which is a small tube of collagen that surrounds both ends of the nerve repair and allows the nerve to heal down the tube, bridging the gap.  Both techniques can allow her function to return when there has been a missing segment of nerve or damaged nerve.  The results are not as good as a direct primary repair of the nerve ends.

For delayed repairs of the nerve laceration, the ends of both nerves must be found in the scar tissue of an already healed wound, freed up and the ends trimmed back to viable nerve.  Often the nerve ends have retracted, and cannot be reapproximated.  In these cases also a nerve graft or nerve tube are utilized.  In cases where a partial nerve laceration has healed, producing a painful neuroma and painful sensation(dysethesia), there is still partial nerve function.  A decision is made at the time of surgery whether to completely divide the nerve, take out the section of scar tissue and repair it were to simply take out a wedge of diseased nerve tissue and in repair that, leaving the more normal appearing nerve intact.  Finally in chronic cases with chronic weakness or deformity and where nerve repair is not felt to be possible. other surgical procedures such as a microvascular nerve transfer, tendon transfers or joint fusions are utilized to restore her hand function.  Each nerve laceration case and patient requirements are individual and unique, requiring a different approach.

Nerve repair surgery is usually performed under general anesthesia to avoid any patient motion which  is significant while operating under pain medication.  The repairs completed and the patient is often placed in a protective splint to avoid any tension on the nerve repair.  The actual nerve repair site takes 4 to 6 weeks to heal and avoid tearing.  Mobilization of the hand is then begun to regain motion.  Return to work and normal activities are usually allowed after the nerve repair site is healed and function and strength are within acceptable limits. Approximately 2 weeks after nerve repair, the nerve starts the slow process of regeneration at about the rate of an inch a month.  regeneration procedure quicker and younger healthier patient's.  Regeneration is faster in primary nerve repairs than with nerve grafts. it may be months before return of sensation as noted.  Return of muscle function often takes longer. it is important to remember that despite our best efforts and advanced microsurgical technique, all nerve function does not return in every patient.