Nerve Injury and Repair
Learn more about nerve injury and repair.
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Nerve injuries are most common in the upper (hand and arm) and lower (leg) extremities. These can be caused by either blunt trauma, such as an impact from a fall or from traction injuries from motor vehicle accidents, or sharp trauma, such as occurs from a direct cut from a knife. In either case, significant nerve injuries require expert evaluation and treatment. In some cases, where the nerve remains partly intact, careful observation and time may be all that is required to achieve recovery. However, in many instances, these injuries will require surgical reconstruction.
Initial evaluation of the patient’s injury will focus on an assessment of the sensory and motor function in the affected nerves. Once the severity of injury is determined, the next step will be either continued observation or evaluation with nerve conduction studies and electromyography (EMG). These studies will be performed by a neurologist to evaluate the electrical function of the nerves and muscles and to determine the location and the extent of the injury. In some cases, MRI may be used to directly image the nerve as well. Serial electrical studies may be performed at bimonthly intervals to look for signs of early recovery. If recovery fails to occur at this point, surgical reconstruction is usually necessary.
Surgical nerve repair involves exploration of the injured nerve and removal of injured tissue or scar from the nerve endings. After that, a nerve can be directly reconnected if there is enough length on the ends to allow for a good quality repair without tension. Repairs are performed with the assistance of an operating microscope to allow for the best alignment of the fiber bundles, called fascicles, inside of the injured nerve. In some cases when a larger amount of tissue has to be removed from the nerve endings, there is too large a gap to allow for direct repair. In those cases, a non-essential nerve will be sacrificed from a separate location on the body (usually from the leg or upper arm) and used to bridge the nerve gap. This procedure is known as nerve grafting. Other approaches for repair such as a conduit, an artificial tube connecting the nerve endings, may be used in particular circumstances when grafts are not possible. Nerve graft substitutes, derived from donated nerve tissues, are also appropriate instead of nerve grafting for some patients.
After a nerve is repaired, the fibers within the nerve begin to grow from the repair site toward the lost target tissues of skin and muscle to restore sensation and movement. This process occurs slowly over several weeks to months, at roughly a rate of 1mm/day (1inch/month) until the nerves reach the intended target. The progress of recovery can be followed by the location of a sensitive area within the reconstructed nerve which will tingle when tapped. These are the advancing nerve fibers within the recovering nerve. Patients will undergo periodic exams after nerve repair to follow the progress of these regenerating nerve fibers. Physical therapy will be done to maintain flexibility and motion in the joints and muscles while the nerve is recovering. When the patient shows signs of recovery with returning muscle tone and contraction, the therapist will begin exercises to strengthen those muscles and restore voluntary movement. As sensation returns, the therapy will also concentrate on retraining the patient to use their sense of touch for better function.
In certain nerve injuries, the damage to the nerve occurs too far away from the affected muscles for recovery to be possible with nerve repair alone. In these cases, additional procedures are available for reconstruction to restore lost function. Tendon transfer procedures are used to take working muscles adjacent to a paralyzed muscle, and substitute the movement of one muscle for another by reconnecting the tendons from the uninjured muscle to the injured one. Therapy will be initiated after the tendons have healed to learn the new movement from the transferred muscle and maximize function.
In an alternative procedure known as a nerve transfer, working nerve branches from adjacent uninjured nerves are reconnected to an injured nerve close to its connection to muscle to restore function. By moving the recovering nerve endings much closer to the target muscles, the nerve transfers are able to restore function to muscles before the damage becomes irreversible. After the nerve recovers, therapy is initiated to maximize the functional gains, as with standard nerve repairs. Sensation can also be restored with nerve transfers of working sensory nerves to nonfunctioning sensory nerves in a related procedure.