February 20, 2018

3-Dimensional Printing in Veterinary Medicine

Used in human medicine for years, this technology is now changing the way veterinarians work and holds great promise for better patient care.
By Don Vaughan
This 3-D printed titanium mesh (placed here over a practice skull) replaced an excised portion of skull in Clubber, a dog with a non-neoplastic lesion.
In August 2017, attendants at Zoo Knoxville in Tennessee became concerned when they noticed that Patches, a female black-breasted leaf turtle, had an ugly wound on one of her nostrils, the apparent result of an encounter with a larger male. The injury stopped growing following treatment with antibiotics and topical ointments, but it left the 30-year-old endangered reptile with a hole on her face that filled with dirt and moss whenever she burrowed.

Zoo staff routinely cleaned the wound using saline, cotton swabs, and tweezers but realized they needed a more permanent solution. That’s when they reached out to the University of Tennessee College of Veterinary Medicine.

After examining the turtle, Andrew Cushing, BVSc, CertAVP(ZM), MRCVS, DACZM, and Kyle Snowdon, DVM, DACVS-SA, suggested a novel fix: a lightweight, 3-dimensional (3-D) printed face mask that would cover the hole without occluding Patches’ vision or interfering with her ability to retract her head.

Micro computed tomography (CT) was used to create a 3-D model of Patches’ head, on which Dr. Snowdon tested a variety of prototype resin masks. The best one, attached with adhesive, lasted just a few months but proved effective.

During the development of the mask, it was discovered that Patches also had a large hole in her hard palate, which presented problems when she ate. “We had to make something that filled the hole in the hard palate but would not fall out or degrade over time,” Dr. Snowdon said. “If the patient had been a cat or dog, we would have done some kind of skin advancement flap in the mouth. But in Patches’ case, there was no tissue we could bring into the area.”

The answer came in the form of a tiny titanium screw threaded through a hole in Patches’ face mask and into a piece of ultraviolet light–cured dental resin that replaced her hard palate. “The mask and the screw help keep the resin in place, and the resin keeps the mask from lifting up,” Dr. Snowdon explained. “It brackets both sides of the hole and seems to work well.”

The doctors wanted a semipermanent fix. “We wanted to make sure that we weren’t doing anything to harm Patches permanently,” Dr. Snowdon said. “We didn’t want something that was so permanent that we couldn’t remove it if needed. The materials in the mask may degrade over years, but replacing it won’t be a big process.”

The 3-D printing technology that saved Patches from a life of misery has been around for decades and is now integral to manufacturing because it can create items using materials ranging from plastic to titanium. In fact, it has become so ubiquitous that even the International Space Station has a 3-D printer on board to produce tools, replacement parts, and other items. “Stereolithography printing, which we used for Patches, was invented in the 1970s,” Dr. Snowdon said. “Titanium or other metals cannot be printed with that technology but, instead, are printed using selective laser sintering or electron beam melting.”

To make a 3-D model, the item must first be scanned—CT is used most often for medical models such as bones—and then the image is uploaded to a 3-D printer, which meticulously models the item, layer by layer, until an exact replica is produced. It can be a time-consuming process, taking several hours to print a bone and up to 24 hours—or more—to print a skull. (A full dog skeleton, created as a teaching tool at Auburn University College of Veterinary Medicine in Alabama, required more than 8 days of continuous printing.) But once a file is created, an infinite number of copies can be printed.

Human medicine has been using 3-D printing for years, and veterinary medicine is quickly catching up. “There are 3 areas in which 3-D printing has revolutionized how we do things,” Boaz Arzi, DVM, DAVDC, DEVDC, associate professor of dentistry and oral surgery at the University of California, Davis (UC Davis), School of Veterinary Medicine, said. “One is surgical planning, the second is resident and student education, and the third is owner communication.”

Surgical Planning
Some of 3-D printing’s greatest benefits are demonstrated in surgical planning, particularly in the treatment of angular limb and skull deformities, oral/maxillofacial fractures, and mandibular reconstructive surgeries. Before the development of 3-D printing, veterinary surgeons commonly relied on x-rays and CT for imaging, but the 2-dimensional representation limited what they could learn. Vital information about the injury and surrounding tissue sometimes remained unknown until the patient was in surgery.
Following a dog attack that left her jaw shattered, 4-month-old Loca was treated at UC Davis, where the team used 3-D models produced from CT scans (top) to print a customized resin exoskeleton of the dog’s face to serve as support for her healing bones (right). Loca recovered well and was eating soft food soon after surgery (left).

“The amount of information we can get from simple radiographs is somewhat limited with regard to our understanding of the exact nature of the deformity,” said Jonathan Dyce, VetMB, MRCVS, DSAO, DACVS, associate professor of small animal orthopedics at the Ohio State University Medical Center Hospital for Companion Animals in Columbus. “We can improve that understanding with CT and generate a virtual image in CT, but 3-D printing allows us to actually get it in our hands.”

Indeed, the ability to print a detailed, life-size model of a damaged bone has been a sea change for orthopedic surgery. Perhaps the greatest advance involves the ability to practice on a 3-D model of the damaged bone before surgery, as well as preselect and precontour titanium plates, a process that can save considerable time in the operating room.1 “Having rehearsed the surgery and appropriately contoured implants before we move into surgery simplifies the procedure,” Dr. Dyce said. “It allows us to do it through more minimal approaches, reduces surgery time and, hopefully, improves the quality of the end result.”

Another benefit of 3-D printing is the creation of custom cutting and drilling guides, which are specially contoured to fit over a bone to give a surgeon a more accurate cutting line. At the University of Tennessee College of Veterinary Medicine, cutting guides are commonly used in the treatment of angular limb deformities and spinal surgery, Dr. Snowdon said.

Thus far, most cases requiring some aspect of 3-D printing have involved dogs and cats, but other species have also benefited, as illustrated by Patches and her face mask. Another example is Pete, a blue-crowned mealy Amazon parrot owned by a family in Allentown, Pennsylvania. When Pete lost a leg to a hungry fox, his owners raced him to Ryan Veterinary Hospital of the University of Pennsylvania School of Veterinary Medicine (PennVet) in Philadelphia. Doctors there successfully amputated the damaged leg below the knee, but they knew that having only 1 leg could cause a host of medical issues for Pete, including painful arthritis. They decided to create a prosthetic leg via 3-D printing, enlisting the help of the Fabrication Lab at the University of Pennsylvania School of Design. The first attempt looked like a bird’s foot but couldn’t support Pete’s weight. A second leg, which looked more like a boot, proved more successful.

Doctors at PennVet also used 3-D printing to treat Clubber, a dog that developed a rapidly growing, non-neoplastic lesion on his skull that eventually pressed against his eyes and nose. Treatment required removing a portion of Clubber’s skull, so the Fabrication Lab printed a precise 3-D skull model on which surgeons could practice in advance. The surgery went well; prefit titanium mesh—commonly used in human brain surgery— replaced the excised section of skull, and Clubber made a full recovery.

“Literally the day after the operation, my coworkers and I were able to meet Clubber, which was pretty fascinating,” Stephen Smeltzer, the lab’s digital fabrication manager, said. “It was amazing to see how responsive he was after brain surgery. It blew my mind.” Smeltzer also helped create Pete’s artificial leg.

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