By Meghan Sullivan, DVM, DACVS
The technology of 3D printing has made tremendous strides in regard to materials and techniques used by medical and veterinary professionals allowing new applications in everyday procedures. Additive 3D printing works by laying down material in thin layers on top of each other which, when cured, form a full model. Imagine a simple desktop printer: if it printed a single square on a page, it would be a 2D printer. If it were able to print numerous squares on top of each other, these squares would stack up into a cube. This is the basic premise of additive 3D printing.
Figure 1: Image of 3D printed hearts with color coding for different working attributes used in teaching
There are a wide variety of materials available including rubbers, plastics, ceramics, metals, and glass. The plastics can range from soft and flexible nylon that allows for dynamic functionality to plastics with glass fibers inside for increased rigidity and structural strength. Adding color and fillers allows for specific blends and unique applications such as training models, functional prosthetics, and lab fixtures and equipment.
In order to make a 3D model, the 3D data is acquired (such as from MRI or CT), processed, numerically modeled, and printed. One study found that 3D models of bone were more accurately represented when data was acquired using CT versus MRI.1 The medical information from the CT or MRI is exported as a DICOM (digital imaging and communications in medicine) file to be used in a software that is compatible with the printer which helps to create the 3D model. The cost of imaging for CT or MRI can be quite high but the cost of making the 3D model can be low in comparison; often the materials are less than $50 depending on the materials used.
Figures 2 & 3: https://tripawds.com/2015/10/21/pet-prosthetics/
In human medicine, 3D models have been reported to be used in spinal surgery, maxillofacial surgery, oncologic, cardiovascular and visceral surgery, and pelvic surgery. The models have been shown to improve the diagnosis and treatment of pathology. They also help surgeons to prepare for complex and risky operations and allow them to have a chance to practice on a patient-specific model which is to scale. It can help the surgeon be prepared for the potential risks and complications prior to the actual live surgery.2 Several papers have shown that 3D printers/models may reduce operation times, complications, and the cost of surgery rooms overall.1 In Japan, the cost of a 3D printed model used for surgery is covered by insurance.2
Having a model in advance can help to customize instruments and devices such as plates that will be used for that specific surgery. Models can also be used in bone replacement or prosthetic devices. They have also been shown to help train veterinary students/medical students to allow training prior to working on live patients.3 3D printing can also aid in the position of radiation for cancer treatment and to create implants to be used for jaw fractures and prostheses. Bioprinting is the printing of live cells and tissues which are then implanted into the body.
One of the most common surgical applications for 3D printing in veterinary medicine is for angular limb deformities. CT is useful for angular limb deformities but does not give the full picture of complex multiplanar deformities. 3D printers can help the surgeon physically examine the angular deformity and make an accurate treatment plan. Once an angular limb deformity model is created, surgeons can practice the correction in advance. This will help to ensure the best surgical approach and fixation, facilitate shorter anesthesia time and potentially reduce infection rates. Once the model is created, the angular deformity is measured and a wedge is cut from the bone and a bone plate and screws or an external fixator is placed to allow stability for the bone to heal. For example, DICOM data from CTs were used by the surgery team at Angell to create 3D models for angular limb deformities. The model is then used to practice surgery and plan for the correction in advance.
Figure 4: The above picture is a 3D printed model of a canine forelimb which was printed at Angell Animal Medical Center in preparation for angular limb correction surgery.
On occasion, a patient will present with a more complex disease process causing lameness such as a malunion from an old trauma. In this situation, often radiographs are not sufficient to completely evaluate the severity of the injury and abnormal conformation. A 3D printed model in these cases might help to decide if there is a surgical correction option and the prognosis. Another example of a challenging case is a young, year-old Labrador who presented for lysis of the patella from infection which caused severe destruction and irreversible damage of the patella. A 3D printer was used to create an implantable patella prosthetic for the dog using a PC-ISO based polycarbonate polymer. After aggressive physical therapy, the patient has been walking increasingly well since surgery. (See figures 5&6 of the lysis on radiographs and the 3D printed model).4
Figures 5 & 6: The picture on the left is of a lateral stifle radiograph which shows aggressive lysis of the patella and also of the distal femur. The picture on the right shows the 3D printed bone model of the same case to prepare for surgical implantation of the patella into the patient. Case and pictures courtesy of Dr. David Hummel at Skylos Sports Medicine, MD.
3D models can also be performed to help assist with neurologic surgery. For example, a model was created on a two pound Yorkshire-Terrier with an atlanto-axial subluxation.1 This could also be used for a vertebral fracture to assess the fracture configuration and complexity and to properly plan the type of repair needed for stabilization. Practicing complex brain surgery in advance can also be facilitated by having a 3D printed model of the particular brain tumor prior to the actual surgery.
Printing a 3D printed skull in advance can help in numerous ways for maxillofacial surgery. It can help to accurately determine the extent and location of a cancerous mass or trauma/injury. It can determine resectability or see how close lesions are to the patient’s brain or eyes in order to plan the best possible approach/repair. Similarly to orthopedic surgery, it can also help to choose implant or plate sizes prior to the procedure. 3D printing is also extremely helpful for maxillofacial surgery such as a horse with a comminuted orbital fracture and TMJ which was assisted by evaluating a 3D model preoperatively.5 Printing 3D models helped in one study of three dogs with orbital and peri-orbital masses. The authors found that this helped to improve surgical planning and provided another modality to visualize the full extent of the disease.6
Figure 7: The above picture is a 3D printed model of a canine skull which was printed at Angell Animal Medical Center.
3D models have also been evaluated for assisting veterinary students’ education. One study compared the efficacy of textbooks, computerized models, and 3D printed models in teaching anatomy in MRI images of the distal equine limb. The results found that 3D models help students to perform better and have a better learning experience.1 In human medicine, a study found that surgeons were able to practice procedures on 3D models in a standardized format which may help to minimize the need for cadavers.7
Some of the main limiting factors of 3D printing are the size limitations and time limitations for creating a 3D model. Most often, the largest size that is able to be printed is a 6” cube. For example, Angell’s current 3D printer can print a model which is about the size of a canine skull. But in order to print and practice for an angular limb deformity, the limb would be printed in two sections (if it is a large patient) and then placed together to create one specimen. The biggest limitation for 3D printing currently is the amount of time required to print the model which can be almost 24 hours depending on the printer. For this reason, the main application of 3D printing to veterinary medicine is for elective planned surgeries to study in advance. It will not be useful for emergent cases which do not allow for enough time to print the sample model. 3D printing is a technological tool that can help doctors to fully assess pathologic disease in order to plan surgical cases, create or prepare implants, study and practice surgical technique and many other goals to help our animal patients.
With clinical help from David Elentukh and Megan Kudzma.
1 Hespel A-M, Wilhite R, Hudson J et al. Invited Review-applications for 3D printers in veterinary medicine. Vet Radiol Ultrasound Vol 55. No 4, 2014, 347-358.
3 Waran V, Narayanan V, Karyppiah R et al. Injecting Realism in Surgical Training- Initial Simulation Experience with Custom 3D Models. Journal of Surgical Education. 2014. 193-197.
4 Case in progress- case and pictures courtesy of Dr. David Hummel at Skylos Sports Medicine, MD.
5 McMaster M, Caldwell F, Gillen A et al. Reconstruction of a complicated orbital depression fracture with medial wall and globe repositioning in a horse: a collaboration across disciplines and specialties. Veterinary Surgery 2016. 45; 529-535.
6 Dorbandt DM, Joslyn SK, and Hamor RE. Three-dimensional printing of orbital and peri-orbital masses in three dogs and its potential applications in veterinary ophthalmology. Veterinary Ophthalmology 2017. 20:1, 58-6.
7 Waran V, Narayanan V, and Karuppiah R et al. Injecting realism in surgical training- initial simulation experience with custom 3D models. Journal of Surgical Education 2014.71:2, 193-197.