UCI Researcher Offers New Hope in Surgical Repair of Severed Nerves

A new technique developed by UC Irvine researchers to reattach severed nerves appears to restore normal motor function significantly better than present methods.

So far, UCI neurobiology professor John Swett, the lead researcher, has demonstrated the technique only in rats. He said he may need three more years of study before he can try the technique on human volunteers.

But Swett said the “freeze-trim” technique, which involves freezing and hardening the ends of the nerves before they are reconnected, could “revolutionize” surgical repair of damaged nerves.

The technique typically restores 71% of motor function in a damaged limb, contrasted with about 18% recovery by traditional suturing, Swett said. The research is supported by a three-year $300,000 grant from the National Institute of Neurological and Communicative Disorders and Strokes.

Dr. Carmine Clemente, a UCLA anatomy professor and former director of UCLA’s Brain Research Institute, called Swett’s findings “a significant new development” that eventually may aid those with gunshot wounds or people injured in car accidents.

“Neurosurgeons have quite a problem in getting successful regeneration--in getting the alignment of fibers to regenerate in their former paths or to reach muscles,” Clemente said. “Dr. Swett has increased the possibility of successful regeneration of nerves.”

To study nerve repair, Swett and his research team cut a rat’s sciatic nerve, the nerve controlling the muscles of the foot, ankle and toes.

In traditional reconnection surgery, the damaged nerves would be sutured together. But Swett said that rat usually does not recover full motor function, because the fibers of the damaged nerve degenerate and nerve cells spray out in a mushroom-like shape.

When those nerve ends are pressed together, “they’re going to bend, like a bunch of wet spaghetti,” Swett said. If sutured together, some of the nerve endings will become scrambled and attach to the wrong nerve fibers, sometimes to those that control opposing muscles.

The result of this scrambling has been that the rat drags his injured foot and cannot walk properly after the surgery, he said.

Swett’s solution has been to freeze the damaged nerves for a minute or two at about 2.5 degrees centigrade or less, then neatly trim the hardened nerve endings and suture them together. The “freeze-trim” procedure prevents the nerves from bending and enables matching nerve endings to be sewed together.

The result is the rat recovers most motor function in the foot, Swett said.

He said his team is still working to devise a proper probe for freezing the nerve endings. Also, his team is studying how to track the recovery of damaged sensory nerve endings and can already reattach motor neurons.