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Models help doctors plan surgery
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Them bones, them bones, them extruded plastic bones.
A collaboration among Boise State Kinesiology, Engineering and Radiology Departments is helping doctors plan complicated spine and joint surgery before they ever touch a scalpel.
Using the rapid prototyping machine located on the fourth floor of the engineering building, mechanical engineering professors Steve Tennyson and Joe Guarino create precise models of the knees, hips, spines and other body parts about to be operated on.
“We’ve been doing this on an experimental basis with Idaho orthopedics,” said Tennyson.
Ron Pfeiffer, a Boise State kinesiology professor who provides anatomical expertise, said the models allow surgeons to rehearse surgery before they actually begin.
“It helps the surgeons prepare, which can improve the outcome for the patient,” he said.
The process begins with data from computerized tomography (CT) and magnetic resonance imaging (MRI) scans of patients, which create individual cross-sectional pictures that look like slices of the body.
This data is then electronically transferred from Intermountain Medical Imaging.
According to Tennyson, MIMICS software uses these sections to create a virtual model. At this stage, the image can be viewed and manipulated in the computer.
This model is made into layered files for the rapid prototyping machine, each containing information for the interior and exterior of the bones.
“The machine actually has greater accuracy than the scan,” Tennyson said. “So we’re not losing any resolution when we’re making the model.”
The machine creates the models by extruding plastic from a set of nozzles one layer at a time.
Tennyson said the plastic is soft when it is first extruded, so the machine must also provide a support structure for any overhanging pieces.
He said this support is made from a brittle plastic extruded from another nozzle, building from the ground up, if necessary.
“It took the software a lot of time to figure out how to add support for these models,” Tennyson said.
The plastic is then washed away in an ultrasonic soapy bath after the model is completed.
Tennyson said an experimental half-scale pelvis took the machine 50-60 hours to complete.
The prototyper was originally purchased in 2000 with a $308,000 two-year matching grant through the Economic Development Administration and the university to provide modeling capability for industrial engineers.
“25 to 30 percent of the machine usage is for industry,” Tennyson said.
Prototyping is a regular part of most manufacturing. Instead of time-consuming methods involving clay, wood and metal, rapid prototyping can save time and cut costs.
“A problem is that the machinery is expensive,” Tennyson said.
He said only a handful of companies manufacture the equipment worldwide, and do not mass-produce it, keeping costs high.
Mechanical engineering students use the machine to flesh out some of their own designs, and have become critical in the prototyping process, Tennyson said.
“We hired some students, who have become experts. We rely on them now,” he said.
While industry is slowly beginning to see the benefits of the prototyping technology, Tennyson said using the process in medicine is still in the experimental stages.
“None of the insurance companies offer coverage for this,” Tennyson said.
There also seems to be some reluctance to modeling on the part of surgeons who pride themselves on being able to read two-dimensional scans prior to operating, he said.
“It’s kind of a macho thing, like pilots flying blind through clouds,” he said. “They take pride in their skill.”
However, Boise orthopedic surgeon Kevin Shea, who specializes in pediatric surgery and assists the group, said he has used the models to prepare for six patients since last year.
“There are certain risks associated with spinal surgery. Having a model of the spine allows us to plan the surgery more completely and do it more safely,” he said.
Matt Neznanski
