Peripheral nerve surgeons can treat foot drop, which is caused by paralysis of the muscles below the knee that lift the front part of the foot, resulting in a foot that “hangs” at the ankle.
A person who has foot drop may have difficulty walking and may need to wear a brace on the leg. Possible causes of foot drop include lumbar disc herniation, damage to the peroneal nerve (usually near the knee) or damage to the nerve above the knee. A foot drop can begin after an injury to the back or leg, an operation on the knee, or even activities such as squatting for prolonged periods of time or crossing the legs.
When the weakness is due to compression of the peroneal nerve, a simple operation can be performed. The peroneal nerve runs around the neck of the bone on the outside of the leg (fibula) just below the knee. It then runs under a muscle that frequently has a tight fascial edge (the peroneus longus). At the point where the nerve runs under this muscle, this tight spot can be released and pressure eliminated. Many times, this is all that is required to restore function to the foot.
At times, these procedures will not be sufficient to restore the function of the foot. In such cases, nerve transfers can sometimes be used. This procedure involves taking nerves with less important roles, or branches of a nerve that perform redundant functions, and transferring them to restore function in a more crucial nerve that is severely damaged.
A nerve transfer for correcting foot drop may involve taking branches of the tibial nerve, which supplies muscles that push the foot down, and transferring them to nerves that supply muscles involved in pulling the foot up. Either the branches of the tibial nerve that innervate the muscles that flex the toes or those that contribute to flexing the calf muscles may be used as donor nerves.
After this procedure, patients will still be able to push the foot down. However, as they regain function from the nerve transfer, they also will be trained to use these muscles to pull the foot up. The brain then learns this process, and the patient is able to pull the foot up simply by thinking about pulling the foot up. This can be a difficult transfer to re-educate and may require a physical therapist to help patients learn this technique. Recovery of function after nerve transfer is a long process. Patients generally see small signs of recovery three to six months after the operation, but in most cases, return of movement takes six to 12 months.