Rapid prototyping in the form of both additive and subtractive technologies is being put to good use in operating rooms as well as design labs. For example, it's providing such good guidance for surgeons that they are spending less time in the OR. In addition, RP tools can precisely machine real bone for implants, as well as assist in the design of functional surgical tools. Here are a few examples.

Presurgical planning

The 3D Medical Applications Center at Walter Reed Army Medical Center in Washington, D.C., doesn't use its 3D printer from Z-Corp., Burlington, Mass., (zcorp.com) to manufacture a new product. But the creative ways the lab does use the machine shows the many possibilities of additive fabrication. The lab has several different kinds of RP machines. A particular project dictates which printer or sterolithography machine the center uses. In general, the lab takes fine-resolution CT scans and runs them through special software to export STL or Z-Print files. These files can be built into 3D objects.

The center says the Z-450 machine comes in handy to print anatomical models for presurgical planning, as well as for implant design, prosthetic design for facial prosthetics, and the prebending of fixation devices. For example, the center has printed models of the main arteries inside one patient's skull. The Z-450 machine prints in color, which the lab says clearly separates the vessels from the surrounding skull and gives a surgeon a better view of problems such as aneurysms and arterial venus malformations, than would a 2D X-ray.

The machine is also useful in printing what the lab calls facial “masks.” This project, which is in conjunction with The National Naval Medical Center in Bethesda, Md., uses the masks in the construction of facial prosthetics, such as for an eye or nose region that may have been removed due to cancer or injury. Here, instead of a CT scan, a special camera takes 3D images. These can be rotated and include a face's color-texture. Some computer manipulation adds thickness behind the image so the Z-450 prints a solid. Basically, the solid is a color copy of the person's face in 3D. The lab then makes the prosthetic on the copy of the person's face.

In the past, this procedure would have entailed having the patient lie down. A nurse would then put plaster over the patient's face. The patient would breathe through straws in his nostrils. Accuracy, however, is affected by the weight of the plaster, which can change the contours of the person's face. Also throwing things off was the gravitational effect from lying down, as opposed to sitting or standing as he would be once the prosthetic were in place.

In another example, a patient with bony tumors from a genetic disorder had a tumor in his knee and growing too close to an artery and nerve. The lab printed a model with the tumor and the nerve in different colors. The surgeon used the model to align his osteotome, a surgical chisel. He then took the tool directly to the patient, while holding the same alignment.

Finally, the lab also uses the RP machine in facial-reconstruction surgeries. Some patient's facial injuries produce complicated cases, such asfrom gun-shot wounds or blasts where metal has penetrated their faces and broken bones. The lab prints a face using little cylinders to support bone fragments. This helps the surgeon see breaks and free-floating bones in relation to the rest of the facial bones. After surgery, the lab can print a post-operative model, which features titanium fixations holding the fractures and bone fragments together. The lab prints the fixations in a different color so the surgeon can see exactly where they were placed. Some surgeons say this capability has cut one to six hours off operating time, depending on the nature of the wound.

Spine implants from bone

AlloSource, Centennial, Colo., (allosource.org), a non-profit bone and tissue provider, machines custom implants out of bone with desktop milling machines from Roland DGA, Lake Forest, Calif., (rolanddga.com). The MDX-540 machines quickly produce parts used in spine-fusion surgeries.

“The desktop mills work well for making custom spine implants,” says AlloSource president and CEO Thomas A. Cycyota. “The machines come complete with CAM software that provides a seamless workflow with 3D CAD. The machines are also resistant to our extensive sanitation procedures, a feature vital to us. The mills are a big improvement over current clinical processes, such as mass-producing one-size-fits-all parts, or tediously hand-sculpting custom parts. And a wide range of FDA-approved materials is available for other implant applications.”

Surgical prototypes, to go

It's no secret that doctors no longer make house calls. But in a new twist, spinal and cranial surgeons can “make house calls” to a prototype lab — not to see patients, but to watch their ideas for new surgical devices take form. Labs in Memphis, Tenn. and Rossi, France let engineers working with Medtronic's Sofamor Danek, (sofamordanek.com) build working prototypes with an in-house FDM machine from Stratasys Inc., Eden Prairie, Minn., (stratasys.com).

“The lab usually sees one or two surgeons daily,” says design engineer Richard Franks. “Each surgeon would explain a concept to an engineer, who models the idea in ProEngineer. The CAD model is then exported to the FDM machine and the doctor often has a prototype in his hands by the next morning. Sometimes he gets it on the same day.”

In a recent design, lab engineers helped a surgeon prototype a ratcheting counter-torque instrument intended to fasten set-screws to a corrective implant on a patient's vertebrae. After the tool fixes the screws in place, the screw heads shear off at a pre-set torque level. The idea is to eliminate surgeons having to use two separate tools, working them in opposing directions and with both hands. This complex activity caused abrupt movements that might harm the patient.

“The prototype combines two existing tools into a single unit,” says Franks. “As the surgeon squeezes the handles together, the ratchet tightens the screws. Surgeons can be rough on prototypes while trying them out, so a tough material is needed. FDM uses polycarbonate, which provides the required strength and durability.”

Prototypes also reduce miscommunication, says Frank. “After sending the ratchet to three hospitals, Sofamor Danek learned that the tool design could be improved by rotating its handle 90°, information the lab might not have learned without a working prototype,” he says. “The FDM machine makes it easy to refine designs before cutting metal, which cuts our costs exponentially.”

The RP lab also produces prototypes for Medtronic's several divisions. “Each has a dedicated engineering staff with different modeling requests,” says Frank. “Almost everything that comes off the FDM machine is for functional evaluation. Building prototypes in-house saves the company a lot of money versus sending the work out.”