Going Out on a Limb
Nerve surgeon Susan Mackinnon has new ways to save arms and legs
Lynn was in surgery the next day. First, there was a patch job. Mackinnon took pieces of a nerve from the back of Lynn's leg--it carries sensation from the back of the heel, something Lynn was willing to sacrifice--and laid them into the gap between the cut nerves in his shoulder. Acting like a trellis, the leg nerve provided support and direction for Lynn's own nerves to regrow from the shoulder back down to the remnants in the arm.
Mackinnon also did some rewiring in Lynn's arm, called a nerve transfer. "It's a tricky idea," she says. "It's like having a broken wire for your kitchen light, but instead of bringing a new wire to it from some central junction box, you run an extension cord in from the nearby pantry, where the wiring still works." For instance, if the nerve that bends the elbow is broken up high, near the shoulder, there's a way around it. There's another nerve nearby that makes a complete run down to the hand. Delicately, Mackinnon can divide that nerve, take a branch, and sew it into the elbow nerve. It takes a while, but the brain eventually learns that the nerve, which used to lead to one muscle, now has branches that lead to two, and it can select which branch to signal. Then it can clench the hand, and also bend the elbow. Surgeons have done transfers for many years, but Mackinnon has come up with new splices, particularly in the upper arm. All Lynn knows is "she gave me my arm back."
That kind of restoration is what Mackinnon has always wanted to do. "I got interested in nerves when I was a med student in Canada studying neurology, back in the 1970s," she says. "Figuring out what was wrong with them was a fabulous intellectual challenge." But diagnosis was a long way from treatment. "We couldn't really do anything for patients," says Mackinnon. "So I switched from neurology to something that had more 'doing': general surgery." That led her to a job at a hospital in Toronto, where she met a neurosurgeon named Alan Hudson who was interested in nerve regrowth. He pushed her to solve the problem. "So I came full circle, back to peripheral nerves. But this time," says Mackinnon, "I could actually do something." It was with Hudson that she did the first nerve transplant.
Excellent results. While transplants get the headlines, "nerve transfers are really where it's at," Mackinnon says. "With transplants, I have to put my patients on immunosuppressive drugs for years so they don't reject the donor nerves, and that's scary. There's too much risk of infection." Hoping to avoid these drugs, Mackinnon runs a lab funded by the National Institutes of Health--one of only a few surgeons to get such support--that's developing methods to neutralize donor nerves so the recipient's immune system doesn't react to them. She does about one donor transplant per year, when a patient doesn't have enough nerve left for any other procedure. But she's much happier doing grafts and transfers. She has performed such transfers on nearly 350 patients over the past decade. "And they have excellent results almost all the time. I'd like to say 'all the time,' but surgeons don't like to jinx themselves," she says. "These people recover normal movement, regain strength, and can use their arms and hands."