3-Dimensional Printing in Veterinary Medicine

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.”

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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. At UC Davis, Dr. Arzi and colleagues recently worked with the College of Engineering to create a protective 3-D printed resin mask, known as Exo-K9, for Loca, a 4-month-old Staffordshire bull terrier. A severe bite by another dog fractured her right zygomatic arch and mandible and extensively damaged her temporomandibular joint. The mask fit Loca’s head perfectly, offering an extra layer of protection as she healed from surgery.

The Auburn University Veterinary Teaching Hospital also has turned to 3-D printing for help with difficult cases. One involved a horse that had been kicked in the face, resulting in a complicated eye fracture. Faculty created a 3-D printed model of the horse’s head to determine which implants to use, among other critical decisions.

The holy grail of veterinary 3-D printing is the modeling of specific body parts for implantation. This is a fascinating area of research, especially on the human side, but high manufacturing costs, problems with rejection, and other issues must be resolved before veterinary surgeons can put it to practical use, experts say. “Custom-shaped implants will likely be part of the future, but we still need to refine [the process] from a biomechanical and biological perspective,” Dr. Arzi said. “It must be more biologically acceptable. Soft tissue is not going to be attached to metal, so we need to understand this much better.”

Evelyn Galban, DVM, DACVIM, clinical assistant professor of neurology and neurosurgery at PennVet, sees an especially bright future for 3-D printing in the treatment of spinal problems in dogs. “A lot of our patients have a spinal malformation in which the vertebrae did not form normally, resulting in instability,” she said. “Many different surgeries can be performed to try to correct that instability, but often we need to find some way to stabilize the spine. With 3-D printing, we should be able to print a stabilizing device that will fit exactly to the abnormal curvature, and pin it into place.”

Student Education

Student education is another area that has benefited greatly from the growing use of 3-D printing in veterinary medicine, instructors say. Rather than relying solely on

A red wolf skull being printed on a Zortrax M300 printer.

textbooks, simulations, and other 2-dimensional materials, students can physically hold and practice on modeled bones and other body parts.

“3-D printing allows me to teach people who are tactile learners or who need that tactile information to be better at their jobs,” said Dr. Galban said. “I can print out whatever piece I want them to understand, and they can hold it in their hands and look at it from every angle. If they break it, we can make a new one.” The result: better, more in-touch doctors. “I think that being able to understand things in a more realistic and 3-dimensional way improves [students’] performance,” she said.

Dr. Dyce agrees. “I think students much prefer having something that looks like a bone in their hands,” he said, as opposed to “plumber’s pipe” sawbones traditionally used for practice. In addition, 3-D models are extremely helpful in custom building surgical solutions for deformities. “For example, we can rehearse total hip replacement and see exactly what size and orientation of implant we may be placing into dogs that have a complex deformity around the pelvis, a spinal anomaly that causes pelvic torsion, or chronic dislocation of the hip,” he said.

According to Christopher Walker, PhD, assistant professor of anatomy at North Carolina State University (NCSU) College of Veterinary Medicine in Raleigh, 3-D models are especially useful from a teaching perspective because they are “durable, replaceable, recyclable, and customizable.”

“In the anatomy lab at NC State, we have a lot of fantastic teaching models, like plastinated organs and wire constructions showing nerves and blood vessels, many of which were made in the late 1980s,” Dr. Walker said. “They are fragile and not easily reproducible, so if something breaks, you have to remake the whole thing or spend a considerable amount of time repairing it. My lab has been 3-D scanning a lot of these older models to create a digital archive. Now, if something breaks, we can simply print it out again.”

Like most veterinary schools, the NCSU College of Veterinary Medicine has “bone boxes” containing complete dog and cat skeletons that students use as learning resources. Because of anatomic variations across breeds, however, the bones are not interchangeable. “If something breaks in one of the bone boxes, you can’t just substitute a bone from another breed, because it’s not going to match,” Dr. Walker said. “So, we just completed scanning a domestic dog skeleton, which can be found on the website morphosource.org, a repository for 3-D anatomic data that is free to access. Now our students can go to this website, download an entire dog skeleton as needed, and study it on their computer or print out specific bones in the library.”

Dr. Walker and colleagues have used 3-D prints for other applications, as well, including an inner ear model that he sectioned from a CT scan and then magnified. “Inner ears are so tiny that they are not something you can easily appreciate in the anatomy lab,” he said. “It’s very difficult to dissect out the inner ear structures; 3-D printing makes the anatomy much more accessible for our students.”

Client Education

Using 3-D models also helps veterinarians educate pet owners, advocates say, especially when explaining a complex case or potential treatment. “Now we can create a 3-D model of their pet and show them what needs to be done,” Dr. Arzi said. “It’s much easier for us to deliver the message and for them to understand what we are going to do or what the limitations are. In some cases, it may help them decide that [a procedure] is not what they want for their pet.”

Adds Dr. Galban: “We want every client with whom we speak to be fully on board with how we’re treating their pet. Most of the time we’re drawing sketches and trying to get them to understand anatomy, which very often they have never been exposed to. However, if we can physically show them via 3-D models what happened to their pet and what we’re going to do for it, it invites them to be part of the treatment discussion, which I think is really important.”

Looking to the Future

Most 3-D printing in veterinary medicine is being done primarily at medical schools, teaching hospitals, and specialty practices such as those with a focus on orthopedics. Few, if any, general practitioners rely on the technology to any significant extent because of its cost, required computer expertise, and limited scope in general practice. However, that could change as the cost of commercial 3-D printers comes down and the next generation of practitioners enters the profession with greater computer knowledge.

“When color flat-panel televisions started gaining traction with consumers in the 1990s, a 40-inch plasma screen display cost tens of thousands of dollars. Now, you can buy a 60-inch LED HDTV that is much higher quality for $500,” Dr. Walker noted. “I think that is what we’re going to see with 3-D printing. The quality is going to be better, the cost is going to go down, and perhaps the speed will also improve. I see all of those things leading to a greater use of the technology in multiple venues."

Reference:

• Winer JN, Verstraete FJM, Cissell DD, Lucero S, Athanasiou KA, Arzi B. The application of 3-dimensional printing for preoperative planning in oral and maxillofacial surgery in dogs and cats. Vet Surg. 2017;46(7)942-951. doi: 10.1111/vsu.12683