Nerve Lacerations of the Foot

Five nerves supply sensation and motor function to the foot.  The Saphenous nerve supply sensation to the inner or medial aspect of the ankle.  The multiple branches of the superficial peroneal nerve rundown knee anterior aspect or front of the leg and supply sensation to the majority of the dorsum or top of the foot.  The deep peroneal nerve runs down the anterior aspect of the leg also and supply sensation to the web space in between the big toe and second toe.  A small branch of the deep peroneal nerve also supplies motor power to the small extensor digitorum brevis muscle on top of the foot.  The sural nerve runs down the back of the leg, around the lateral or outer aspect of the ankle and supply sensation to the lateral portion of the foot and fifth toe.  The posterior tibial nerve runs down the back or posterior aspect of the leg, around the medial or inner side of the ankle and split into the medial plantar nerve and lateral plantar nerve before running around to the bottom or plantar aspect of the foot.  The medial plantar nerve supplies sensation to the big toe, second and third toe and motor function to the small intrinsic muscles of the big toe.  The lateral plantar nerve supply sensation to the fourth and fifth toe and motor function to the small intrinsic muscles of the fifth toe.  Each nerve is composed of various sensory and/or motor nerve fibers and is covered by an outer layer noted as perineurium.

After nerve laceration the distal portion (end towards the toes) begins to degenerate in a process called Wallerian  degeneration. The nerve ends may retract from each other in cases of 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 avulsion 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 foot 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 toes or on top of the foot.  .  It usually cannot be tolerated on the bottom of the foot  due to risk of burns or injury ..  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, athlete ).

Early treatment of lacerations usually consist of cleaning or debriding 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, an 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 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 magnification.  The repairs completed and the patient is often placed in a protective boot to avoid any tension on the nerve repair. there is no weight-bearing on the foot at that time.  What I donor with the talus until the The actual nerve repair site takes 4 to 6 weeks to heal and avoid tearing.  Mobilization of the foot 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.