Nerve and tendon lacerations (i.e. deep cuts) of the foot and ankle region are a relatively common injury. Treating it appropriately is important to maintain long-term sensation and motor functions of the injured foot and limb.
Five nerves supply sensation and motor function to the foot:
Each of these nerves is composed of various sensory and/or motor nerve fibers, and are covered by an outer protective tissue layer noted as perineurium.
Following a nerve laceration, the distal portion (end towards the toes) of the nerve begins to degenerate in a process called Wallerian degeneration. The nerve ends may also retract from each other in cases of a complete laceration. Scar tissue then forms at both ends.
In motor nerves, the motor endplate (the attachment of the nerve to the muscle) may also degenerate after a period of time.
All of these factors can work against the complete return of nerve function after repair.
There are many types of lacerations that can contribute to the treatment needs of a patient:
These, other diagnostic studies (which are prescribed as needed), and a very detailed examination the injured foot will all help to provide a complete picture of the functional loss caused by any foot-based nerve laceration.
The original level of injury is also important for doctors to consider. For example, lacerations that injure small and/or mixed nerves (i.e. or both sensory and motor nerve branches) will be more difficult to treat.
Ultimately, all assessments must be coupled with a decision on how much functional loss can be well tolerated in order to create a plan to restore as much function as possible. 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 the risk of burns or injury. However, numbness is better tolerated than pain and hypersensitivity. Additionally, partial weakness, motor loss or lack of coordination are better tolerated in some patients than others (ex. pianist, athlete).
Early treatment of lacerations usually consists of:
Early treatment typically takes place either immediately after an injury or approximately 2 weeks later. In cases treated later, 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 listed above, 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 removed, or is actually 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 different, newer surgical technique involves using a neural tube - a small tube of collagen that surrounds both ends of the nerve repair. This allows the nerve to heal down the tube, bridging the gap.
Both surgical techniques can allow 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:
As you can see, each nerve laceration case and patient requirements are individual and unique, requiring a different approach.
All nerve repair surgeries are usually performed under general anesthesia to avoid any patient motion, which is important while operating under magnification. Afterward, the patient is often placed in a protective boot to avoid any tension on the repaired nerve. There is no weight-bearing allowed on the foot at that time.
The actual nerve repair site typically takes 4 to 6 weeks to heal. 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 surgery, the nerve starts the slow process of regeneration at about the rate of an inch a month. This process is often faster in younger, healthier patients. Regeneration is also faster in primary nerve repairs than with nerve grafts.
It ultimately may be months before the return of sensation is noted. Return of muscle function often takes longer. Additionally, it is important to remember that despite our best efforts and advanced microsurgical technique, all nerve function does not return in every patient.