BME students design 3D printed mask as cast for fractured dog skull
Loca, a 4-month-old female Staffordshire bull terrier, was bitten by another dog so severely that her right zygomatic arch (cheekbone) and mandible (jawbone) were fractured, and her temporomandibular joint (TMJ) suffered extensive damage. In addition, there were multiple puncture wounds on her face and neck.
Faculty members Drs. Frank Verstraete and Boaz Arzi and resident Dr. Colleen Geisbush of the UC Davis veterinary hospital’s Dentistry and Oral Surgery Service (DOSS) knew this would be a challenging surgery due to the extent of the damage, but there were promising aspects to the case. First, Loca was young, which meant there was a good chance that the damage to the TMJ could correct itself with natural bone regrowth – something that may occur in dogs of Loca’s early age. Second, this case offered them the opportunity to utilize a new face mask they developed with biomedical engineering students.
Designed to be used as a cast for a fractured skull while it heals, the mask was the result of a long-standing collaboration between the oral surgeons and the UC Davis College of Engineering (COE). To assist with surgery preparation, DOSS has utilized COE’s Biomedical Engineering (BME) Department many times over the years to 3D print skull models in BME’s Translating Engineering Advances to Medicine (TEAM) Laboratories.
Recently, DOSS has been working with BME students to design an apparatus that could help the healing process of maxillofacial fractures, much like a traditional cast helps leg fractures heal. Drs. Verstraete and Arzi began working with biomedical engineering seniors Patrick Foster, Matthew Ho, Christian Lu, Jennifer Nguyen, Anthony Sorbera about a year ago. BME Professor Anthony Passerini, BME graduate student Christina Rohlf, and TEAM manager Steven Lucero acted as mentors for the project. For the veterinarians, it was a chance to solve a longstanding problem and improve outcomes for injured dogs. For the students, it was a chance to create a senior design project that might make a big difference for veterinary medicine.
The students met with their vet school clients for 4 or 5 months to understand the dimensions of the problem. They did background research and analyzed existing solutions. They incorporated client needs with engineering metrics to come up with a list of benchmark specifications that the solution would aim to meet.
For the next 2-3 months, they brainstormed possible solutions while frequently meeting with the clients for feedback. The team decided to pursue the concept of a 3D printed cast, and developed and refined the process through which to create the virtual model of the cast based on CT scan data. After careful consideration of possible fabrication methods and materials, they decided to use multi-material 3D printing technology from the TEAM lab.
The result was the Exo-K9 Exoskeleton – a custom, 3D printed exoskeleton for dogs with maxillomandibular injuries. This innovative approach to harnessing the capabilities of 3D printing at the TEAM lab could lead to helping dogs with severe fractures where internal fixation is not a possibility due to various limitations.
As soon as Loca arrived at the hospital, Dr. Arzi notified the BME students to be ready to print an Exo-K9 if a CT scan showed that she would be an ideal initial case. School had only been out for one week, and the students, who had graduated, prepared for the real life test of their exoskeleton.
Loca was placed under general anesthesia for a cone-beam CT scan to fully characterize the extent of her injuries. The scan showed the extent of the injuries to her facial bones, jawbone, TMJ, and also a small fracture in the vertebrae of her neck. A salvage surgery was then performed to remove bone fragments from her right zygomatic arch and right caudal mandible.
While Loca was recovering from surgery, the senior design team reassembled and got to work in the TEAM lab printing the first Exo-K9 to be used on a patient. Based on Loca’s exact specifications from her CT scan, the mask’s dimensions would precisely fit her head, and could help optimize the healing process. Located just a quarter mile walk across campus, the TEAM lab is an ideal partner for the UC Davis veterinary hospital. As soon as the mask was finished printing the next morning, the students delivered it to the hospital, where Loca was eagerly waiting to become its first recipient.
Loca did extremely well throughout her 3-day hospitalization. She almost immediately began eating soft food and remained comfortable on her pain medications. In addition to the Exo-K9, Loca was fitted with a padded neck bandage to provide stabilization of her neck fracture and limit her range of mobility during the healing process.
For the next month, Loca was not allowed access to any toys, bones, or anything else hard to chew. Her mask and neck collar remained on at all times except to allow her to eat and drink. She was fed a soft diet until her injuries healed.
Loca returned to UC Davis for a 1-month recheck appointment that involved another cone-beam CT scan to characterize her fracture healing and further assess for any evidence of dental trauma to her permanent developing teeth. As suspected, new bone was forming in the place of her former TMJ. While positive, it would now be necessary for Loca to move her jaw routinely by eating hard kibble to encourage the new formation to become a semi-functional joint instead of a fusion with her skull.
Additionally, she had two developing molar teeth that appeared to be malformed on her right lower jaw. It was unclear at that time if the teeth would erupt normally or if they would need to be extracted. Based on an initial interpretation, the latter was more likely.
Almost three months later, Loca received her third cone-beam CT scan which revealed that her previous surgery sites healed well and that the new TMJ formation was progressing nicely. The CT scan and full-mouth dental radiographs showed that her first and second molars on her right mandible were indeed malformed. Those teeth were extracted without complication.
Loca continues to recover well from her injuries, and all indications show the Exo-K9 to be a viable component to maxillofacial injury healing.