Rod Bender: Building a better tool for spinal surgeries

by Kathleen McCoy  |   

UAA is probably not the place where you imagine sophisticated new surgical tools being invented. But the ingenuity of some mechanical engineering students and their professor resulted in exactly that.

First, a little background.

When human spines go bad, surgeons stabilize them with long metal rods that they actually attach with screws into bones up and down the spine. The rods hold the backbone stable for up to a year or more while parts fuse or mend.

Human spineBending this rod, typically made of stainless steel or a lighter-weight but strong alloy, happens right in the middle of surgery. The doctor shapes delicate curves that match those of the spine he's working to save, then secures the compromised spine to the supporting rod.

Tools to shape the rod are few and limited. One type requires two people to operate. The other type forces the surgeon to leave the patient's side and shape the rod at a table vise across the room. He may need to go back and forth many times.

Mechanical engineering professor Anthony Paris Anthony Paris had a better idea. He teaches mechanical engineering at UAA and does research on designing new or smarter tools.  A better rod bender would be light enough for a surgeon to use with one hand while standing at the patient's side, yet strong enough to bend metal.  It would need to be made of something you could sterilize.

"I'd been carrying around the idea of a Vise-Grip in my head for a long time," Paris said. "It just seemed like a doable problem, creating something with a compound mechanical advantage."

That means a tool that is designed to amplify the force a user applies, advances in incremental steps without slipping backward, and is light enough not to fatigue the hand.

Paris can remember his big ah-ha moment. He was in Boise, Idaho where he lived at the time. He stopped to chat with his neighbor. "He was out in his yard, working on his sprinkler system," Paris recalled. "And he had to cut a piece of PVC pipe."

Watching the man squeeze a simple, hand-held device and slice right through that pipe, Paris thought, "WHOA, that's exactly it!"

The mechanics in a pipe cutter amplify the force the user applies so that the blade can actually sever the pipe. The blade moves forward incrementally and locks, then advances on the next squeeze.

Just like the surgeon with the better rod bender, Paris's neighbor could hold the pipe cutter in one hand, and the PVC pipe in the other. It was a one-person, one-handed job.

Rod bender prototyleIn 2009, he challenged three of his mechanical engineering students to create a working prototype of a rod bender. Their design uses insights Paris and his students gleaned from everyday tools like the ratchet, the Vise-Grip, the PVC pipe cutter and the locking mechanism found on a steel strapping tensioner.

When the student engineering team succeeded, they and Paris filed a technology disclosure form with the University of Alaska, and the students went on to their careers at BP.

Fast-forward a few years to August 2011 and the arrival of a new vice provost of research at UAA. As part of an initiative to commercialize intellectual property, her office began scoping the university for projects that might be patent-worthy. The rod bender was one of them; it now has a patent pending. The university, the students and Paris stand to benefit financially if the device gets licensed for manufacture.

As talks move forward, Paris continues to tinker with the prototype. He's shortening the handle for less weight and better leverage, and adding a spring so the tool can re-open automatically. Each new design modification is rendered at UAA's rapid prototyping lab, a fast iteration in plastic for look and feel.

"It's been great to see them first in 3D," Paris says, "before we mess with cutting a prototype in stainless steel."

Fall semester has been very busy for Paris. In addition to teaching engineering statics and fracture mechanics, he advises students, works on curriculum reform and continues other engineering research projects.

But the rod bender has been keeping him awake at night, thinking and tinkering. He has enough new ideas to generate a third and fourth prototype, and probably even more.

"It's always so hard to know when to stop," he said.

Creative Commons License "Rod Bender: Building a better tool for spinal surgeries" is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.