Susan Mackinnon, MD, is a Washington University nerve repair specialist and chief of plastic and reconstructive surgery at Barnes-Jewish Hospital. And she is considered an international authority on nerve regeneration, nerve transfer and nerve transplant. Mackinnon says, “When I started my own practice in 1982, I asked a single question:
“How can we improve results for patients with nerve injuries?’”
Recently, the answer to that question came in the form of an innovative nerve-transfer procedure she performed that restored some hand function to a quadriplegic patient. The patient had sustained spinal cord injury at the C7 vertebra, the lowest bone in the neck. Instead of operating on the spine itself, Mackinnon and a team of surgeons rerouted working nerves in the upper arms.
Ida Fox, MD, assistant professor of plastic and reconstructive surgery at Washington University, explains the technique this way: “This procedure is unusual for treating quadriplegia because we do not attempt to go back into the spinal cord where the injury is. Instead, we go out to where we know things work—in this case the elbow—so that we can borrow nerves there and reroute them to give hand function.”
Although patients with spinal cord injuries at the C6 and C7 vertebrae have no hand function, they do have shoulder, elbow and some wrist function because the associated nerves attach to the spinal cord above the injury and connect, or “talk,” to the brain. Since the surgeon must tap into these working nerves, the procedure will not benefit patients who have lost all arm function due to higher injuries—in vertebrae C1 through C5.
This particular technique was originally developed by Mackinnon for patients with arm injuries specifically damaging the nerves related to flexion of the thumb and index finger. This is the first time she has used nerve transfer to return limb function after a spinal-cord injury.
Following surgery and a year of intensive physical therapy, the patient regained the ability to pinch his thumb and index finger together. As a result, he can now feed himself bite-size pieces of food and write with assistance. Mackinnon cautions that the technique does not achieve instantaneous results. The brain must be trained to understand that nerves once used to bend the elbow are now being called upon to do something quite different.
Laying the Groundwork
Treatment for nerve injuries has changed dramatically in the past 30 years. Traditional repair involved either joining the two severed ends of the nerve, called direct repair, or shortening limbs to bring the nerves together. These techniques put tension on the nerves, caused scarring and often yielded poor results.
In the early 1980s, nerve grafting, using nerves from cadavers, became a viable option. At that time, Mackinnon began training with a pioneer in this procedure: Alan Hudson, MD, chair of neurosurgery at the University of Toronto. She spent 10 years perfecting nerve-graft techniques. “While the outcomes were better than direct repair, I was still frustrated by the results,” she says. “But I learned a lot in that time and established a great lab with great people.”
Informed by her research, Mackinnon began performing her nerve-transfer technique—a novel procedure for the time—in 1991. “I received a lot of push-back from the medical establishment initially, but I worked hard and collaborated,” she says. “As a result, the medical community around the world has embraced nerve transfer. It’s now mainstream—but it’s taken us decades to get here.”
Mackinnon also is one of only a few surgeons in the United States who performs brachial plexus surgery, which involves the complex labyrinth of nerves branching off the spine at the base of the neck to the chest.
Currently, Mackinnon is working on a technique to treat patients with partial nerve injury. Treatment options for these patients have been limited for many years. This promising new procedure, called supercharge end-toside transfer (SETS), encourages nerve regeneration and increases function.
Mackinnon says, “Throughout my career, I’ve taken the knowledge I gained from lab research into the clinic with patients and then from the clinic back to the lab. This back-andforth over the years helped me come up with answers and changed the way we manage nerve injuries today.”
Sharing Knowledge
Despite advances in treatment, Mackinnon continues to worry that many believe not much can be done for nerve injuries. “We’re just on the other side of a big shift, but we have a lot of education to do with doctors and patients,” she says.
That need for education resulted in a website designed to train other physicians in nerve-repair surgery. “I want all surgeons to get superior results for their patients, no matter where they live,” she says.
The still-evolving site, developed by Ida Fox, MD, and senior research assistant Andrew Yee, was originally intended to train military surgeons who treat the nerve injuries of American soldiers in Iraq and Afghanistan. Since its inception, the website has grown to one that can help any surgeon anywhere learn the techniques Mackinnon has pioneered.
Career Highlights
In March, Mackinnon was one of three physicians in the United States to be honored with the Clinical Excellence Award by Castle Connolly Medical Ltd., which publishes “America’s Top Doctors” and other guides. Mackinnon says she is most humbled by being named the recipient of the 2013 Jacobson Innovation Award from the American College of Surgeons. This honor acknowledges surgeons who have been innovators of a new development or technique in surgery. In Mackinnon’s case, it recognizes her leadership in the field of nerve regeneration and peripheral nerve surgery.