Styles

Stereolithography models enable surgeons to rehearse difficult surgeries and create cutting templates and exact bone grafts before the patient ever enters the operating room. Recently, through the use of stereolithography models, surgeries previously deemed "impossible" due to the complications and risks involved have been successfully performed.

When Graeme Tennick saw the stereolithography (SL) model of his disfigured skull, it gave him hope that one day his face would again assume a more pleasant appearance. Three years before, he had been badly injured in an accident on an English country road while driving back to his office. A drunk driver in a large sedan coming in the opposite direction rammed Tennick's subcompact head-on. The force of the crash shoved Tennick's body into his car's trunk.

Tennick suffered multiple injuries. An arm, ankle and femur, and several ribs and toes were broken, and a lung punctured. But the worst damage occurred to his face. "The whole of my face was pushed in," Tennick remembers. An optic nerve was severed, leaving him permanently blind in the left eye. His left eye socket and cheeks were crushed and his jaw and nose broken. He had a hole in the roof of his mouth.

Tennick was on life-support for six weeks. Though he will never be able to completely straighten his right arm, and his ankle won't ever be completely sound, most of his injuries eventually healed. But doctors counseled him that he might have to live the rest of his life with a disfigured face. His facial injuries were so extensive that no surgeon would attempt the complex operation. To do so could make matters worse.

Then Tennick's primary surgeon learned of stereolithography.

Bone Imaging Software
A nearby company, Styles Precision Components Ltd., was using its Stereolithography Apparatus (SLA) to model components for automobiles, computers, and aircraft. One day Styles Precision received a computer disk from Materialize, a Belgian company. Materialize was marketing software that could take a computer tomography (CT) scan of a human head and filter out the flesh, tissue, and brain, leaving only the image of the bone. With such software, Managing Director Gordon Styles knew his company could make an SL model of a skull, and he had a test model made on an SLA 250.

A local reporter learned of the test and described it to a friend, Keith Postlethwaite, attending surgeon at Newcastle General Hospital in Newcastle upon Tyne. Postlethwaite contacted Styles and asked if they could provide models of skulls for some of his difficult cases, one of which was Tennick's.

With the help of an SL model, Postlethwaite performed his first surgery on another automobile accident victim who, unable to open his jaw, had survived four years on a liquid diet. Basing the surgery on the SL model, Postlethwaite reconstructed the jaw so that the man can now eat some solid foods.

"Model" Surgery
Tennick's was Postlethwaite's third surgery using an SL model. "I saw the model before the operation was performed" recalls Tennick. "Keith explained to me what was going to be done, using the model to illustrate the surgery. It put my mind at ease when I could see just what Keith was going to do."

Postlethwaite had a CT scan of Tennick's head made and supplied the computer file to Styles. A CT scan takes more than a hundred X-rays of the head from different angles so that a complete and accurate three-dimensional image is obtained.

Overnight, a skull model showing minute detail of Tennick's injuries emerged from the SLA. Before the actual surgery, Postlethwaite performed every step of the operation on the model. He used the model as a guide to construct titanium plates to hold bone together and to decide where and how to position bone grafts.

Accurate Representation
"The model is such an accurate representation of the patient that when the plates are put on the patient, they assure that the bones will be positioned correctly," Postlethwaite says. "The model gives you more confidence that you can do the surgery.

"Normal CT scans are only two dimensional. The model being three-dimensional makes it easier to see what the injuries are. Had I not had the model, I would have said that the surgery was too difficult to attempt."

Because Postlethwaite can rehearse an entire operation on an SL model beforehand and use it to construct accurate replacement parts, he saves time during the actual operation, thereby reducing the cost of the surgery and lessening the danger to the patient of hours of anesthesia. Depending on the complexity of the operation, Postlethwaite estimates that modeling can reduce a ten-hour operation by as much as three hours with a cost savings of up to £3,000 (about U.S. $4,500) in the U.K. However, in the United States, several hours of operating room time could easily equate to tens of thousands of dollars.

Increased Surgical Success
Ian Wilkinson, Styles' medical applications manager, worked with Postlethwaite and says that the real importance of the SL model was that it increased the chances of success for the surgeon. "It released him from having to spend time on tedious parts of the surgery so that he could devote time to finer issues. The best surgeon in the world will get tired during such a lengthy operation and his workmanship will fall off."

Other surgeons are learning of Styles' ability to model skulls. The company has developed models for hospital sin London and Doncaster. Wilkinson says use of SL models is ideal for three types of skull deformities: car crash victims with severe injuries, congenital deformities to the jaw and other sections of the skull, and cancers of the jaw. Wilkinson noted that an SL model enabled a Doncaster surgeon to successfully operate on a woman who had jaw cancer. The once speechless patient can talk again.

No Comparison
Gordon Styles is so impressed with the ability of SL to provide accurate models - whether for surgical use or for industrial manufacture - he plans to add an SLA 500 in late 1995. He prefers SL over other rapid prototyping systems. One reason, he says, is that the low porosity of the SL 5170 epoxy resin permits more accurate silicone rubber mold tools. Rubber mold tool developed from other systems' models often are pockmarked. That's because rubber is left behind in air pockets that have developed in the model. To counteract that, Styles continues, other systems must employ an additional step of coating the model with resin to fill in any air holes, adding to the expense of silicone modeling.

"As far as I'm concerned, the only system you are going to get a decent return on is stereolithography," Styles maintains. "And I'm not saying that to get a discount."

But for Tennick and other people with critical head deformities, the major return on SL is not in monetary form, but in its ability to help them return to normal lives. No wonder Tennick calls the SL model of his skull a "godsend."