Q&A: Nerve Transfer Surgery
Q. What is nerve transfer surgery?
A. Nerve transfer is a surgical technique that’s used to restore muscle function or sensation after a serious injury. Employing the technique, surgeons select a redundant nerve — one that serves the same function as another nerve in the body — and connect it to a more important but damaged nerve that’s not working. The nerves must be in close proximity. The rewired nerve can restore muscle function or feeling to the target area, often a hand, arm or shoulder.
Q. How is nerve transfer surgery used to restore a quadriplegic’s hand function?
A. A quadriplegic is someone who has suffered a spinal cord injury that leaves them without the ability to use their hands or legs. Generally, the higher the spinal cord injury, the more profound the paralysis. Nerve transfer surgery has been used to restore some hand function in patients who have suffered spinal cord injuries at the base of the neck (the C6 and C7 vertebrae). These patients tend to have some shoulder, elbow and wrist function, which means they still have some working nerves in their arms.
Surgeons use a nerve transfer to bypass the spinal cord injury, which blocks signals to the brain. They engineer a detour around the injury by connecting a nerve that still communicates with the brain — it joins the spinal cord above the C7 vertebra — to one below the injury that has been rendered useless. The nerve below the injury is the one that controls the thumb and index finger.
The goal of the surgery is to restore a patient’s ability to lift and hold small things, such as a straw, fork, spoon, toothbrush and pen.
Q. How long will it take before the patients can use their hands again?
A. This is not a quick fix. It can take up to a year before patients have use of their thumb and index finger. There are two reasons for the delayed gratification. First, the brachialis nerve must grow down to the muscles that control the hand. Nerves can grow at 1mm per day, so it will be about six to nine months before a patient can expect to experience any kind of new movement. Then the patient has to do intense physical therapy to relearn how to trigger hand movement. That process is more difficult than it sounds because the individual will be using a nerve that used to bend the elbow to move the thumb and index finger. It takes time for the brain to adapt to this new reality.
Q. Why is this surgery important?
A. Quadriplegics lead difficult lives; most need help with daily activities, such as changing, washing and eating. Any measure that provides more movement confers more independence. Being able to manipulate the thumb and fingers allows quadriplegics to manage more small, daily tasks on their own.
The recent surgery at The Ottawa Hospital represents the first time that surgeons in Canada have used the nerve transfer procedure to restore hand function after a spinal cord injury. The procedure remains exceedingly rare and has been used in only 8 to 10 spinal cord patients in North America.
Q. Can it be used in other parts of the body?
A. Right now, the surgery has a number of limitations. First, it is limited by the number of redundant nerves in the body that surgeons can “borrow” to put to use elsewhere. Second, it is limited by the rate of nerve growth following a peripheral nerve injury. Surgeons essentially create a nerve injury when they cut the brachialis nerve and join it to the anterior interosseus nerve. Success is governed by time. The nerve must regrow to the target muscle within 12 to 18 months or else that muscle will become damaged. It means, for instance, that a nerve transfer in the leg is unworkable because of the required distance: By the time the nerve fibre reached its target, the muscle would no longer be responsive.
Researchers, however, are working to speed nerve growth and to preserve unconnected muscles so that they remain receptive to nerve growth for a longer period of time.