3-D printing: Revolutionizing preoperative planning, resident training, and the future of surgical care

When members of the surgical team at Boston Children’s Hospital, MA, opened the skull of 18-month-old Violet Pietrok in October 2014 to correct her congenital facial malformation, they referred to a three-dimensional (3-D) mold created from computerized tomography (CT) images of Violet’s head to perform the delicate procedure.¹ 3-D printing technology, also known as “additive manufacturing” because its production method adds very thin layers of material upon one another to create 3-D objects, allows surgeons to plan where to cut down to the millimeter and to practice complex operations on patient-specific rubber or plastic molds.²

Although 3-D printers have been used in the last couple of decades to create surgical tools, laboratory equipment, and prosthetic limbs, only recently has software been developed to translate a patient’s magnetic resonance imaging (MRI) or CT scan images into a replica of a patient’s organ. Estimates suggest that as of 2015, 75 U.S. hospitals and 200 worldwide have access to a high-level 3-D printer, and that number is expected to grow.³

Fellows of the American College of Surgeons (ACS) are actively using this technology, not only at Boston Children’s Hospital but at other institutions around the country, including Washington University School of Medicine, St. Louis, MO, where surgeons used a 3-D model of Myah McWilliams’ skull to fix the five-year-old’s severe facial asymmetry in December 2015.⁴

In this article, members of the College describe their experiences with 3-D printing models, identify its benefits and limitations, and consider future applications for this technology.

Preoperative planning with 3-D printing

Adnan Siddiqui, MD, PhD, FACS, FAHA, neurovascular surgeon and vice-chair, neurosurgery, Jacobs School of Medicine and Biomedical Sciences, University of Buffalo, NY, has been using 3-D printers as an aid in operations for complex aneurysms for the last few years.⁵ He uses the technology to help him gain a deeper understanding of a patient’s unique vasculature in a way that traditional imaging alone cannot provide, as well as to develop a preoperative surgical plan.⁵

“When you do an angiogram and you take a blood vessel picture or snapshot, a CT angiogram, an MRI angiogram, it looks like, ‘There’s the problem, there’s where I need to go,’” said Dr. Siddiqui, chief medical officer, The Jacobs Institute, Buffalo. “The fact of the matter is, when you try to perform the procedure in reality, the impediments are such that you can’t make your way up there with the tools you have or there is less space in the artery than you originally thought, and you need to make adjustments on the fly.” For example, the surgeon may need to abandon the first approach and try something else, such as entering through the neck rather than the groin to reach an aneurysm.

“What this translates into is multiple procedures, multiple variations, longer procedures, [and] more possibilities for complications,” Dr. Siddiqui said. Employing a patient-specific 3-D model preoperatively may be able to alleviate some of those problems.

Dr. Siddiqui and his colleagues at The Gates Vascular Institute and University at Buffalo, including scientists, clinicians, and trainees, meet weekly to discuss what cases would be best served by the technology. “[Then] we say, hold on, this looks like a complicated case. Let’s 3-D print this entire vascular anatomy, put it in the lab, attach it to a flow pump, and let’s do the whole procedure, from groin to vertex, artificially on the 3-D printed model and work out the kinks,” he said. The advantage of practicing on a 3-D printout is to shift any trial-and-error element for a procedure from a patient to a replaceable model, with the goal of achieving improved outcomes and safer patient care.

“With 3-D printing, we are now able to take some of the most complicated cases—specifically those with lots of nuances to their anatomy that really aren’t appreciable on a computer screen—and generate a model that you can turn around in your hand,” said Albert S. Woo, MD, an Associate Fellow of the ACS and chief, pediatric plastic surgery, and director, craniofacial program, division of plastic surgery, Warren Alpert Medical School of Brown University, Providence, RI. Dr. Woo and Steven Couch, MD, FACS, oculofacial plastic surgeon and assistant professor of ophthalmology, Washington University, used 3-D modeling to carefully reconstruct Myah McWilliams’ orbital deformity while protecting the young patient’s tear ducts.⁴ (At the time of Myah’s procedure, Dr. Woo was associate professor, Washington University, and chief of pediatric plastic surgery, St. Louis Children’s Hospital.)

Dr. Couch noted that a 3-D printed model made preoperative visualization a more tangible experience. “The standard is, you look at a 2-D screen and look at multiple views on the area—so in my case, you look at coronal, axial, sagittal images—and you try to develop a 3-D model in your mind,” he said, and the repositioning or canting of the bone were done mentally. Dr. Couch acknowledges that while surgeons have been doing this conceptualization for a long time, “3-D printing potentially improves our ability to accurately visualize in the preoperative setting.”

A 3-D-printed model was especially useful in Myah’s case, in which a multidisciplinary team needed to work together. “A model allows us to say, ‘My goal is to change this portion, this portion, and this portion. How will that affect your portion of the surgery? Is there a better way to expose this area?’” Dr. Couch explained.

Use across subspecialties

More than a year ago, Washington University obtained a grant to purchase a professional grade 3-D printer, and since then Dr. Woo and colleagues have used the printing lab to optimize the results of several of their patients.

“Initially, I had anticipated that the people who would be the most interested in 3-D modeling would be those who deal with bone deformities—plastic surgeons like myself, or oral maxillofacial surgeons, neurosurgeons, and orthopaedic surgeons. The interesting thing is that the greatest enthusiasm for this technology has actually been from surgeons who don’t work on bones, so to speak, but actually on the soft tissues,” said Dr. Woo.

“Not too long ago, a cardiac surgery colleague was working on a case with an aortic deformity and we were able to model-out not only the heart but the aorta for this young infant who was less than a year old,” said Dr. Woo. “When the cardiac surgery team was trying to decide whether the child needed open-heart surgery versus a cardiac catheterization, we were able to not only print a 3-D model for them, we were able to give the interventional cardiologist the opportunity to choose the texture and the softness of the printed materials so that the model was as close to a normal infant’s [heart] as possible. They could actually practice the surgery on a model that was much more true to life.”

“For orthopaedic and craniofacial surgery, the hard tissue simulation is excellent…because the plastic is roughly the same consistency as bone, so you have a fairly realistic simulation,” said John G. Meara, MD, DMD, MBA, FACS, plastic surgeon-in-chief, Boston Children’s Hospital, MA. In fact, Dr. Meara and his team used several 3-D models to plan the operation on Violet Pietrok. “We had a couple of 3-D-printed models made because I wanted to have the ability to do the procedure on those heads and to develop a couple of osteotomy patterns as backups. We revised the pattern three times before we got to the point where I could see exactly where the cuts needed to be.”

This exacting preparation was a key element in correcting the young girl’s rare facial deformity. “Violet had a complex Tessier cleft, and we did a facial bipartition—we moved the two halves of her face closer together,” Dr. Meara said. “The preoperative planning was very helpful because we actually did the surgery on the 3-D printed models to give us an idea of how the orbits would come together,” he added, explaining that he and his surgical team made subtle changes in the way they had initially planned to cut the bones based on potential interference in the affected area. Similar to Dr. Siddiqui’s experience, Dr. Meara found that he “didn’t have to revise things in the OR [operating room] because we were able to make those adjustments on the model beforehand.”

A tactile understanding of the procedure translates into increased confidence for the surgeon going into that nonstandard operation, and, according to Dr. Meara, the 3-D-printed models also are useful inside the OR.^1,6 “Even in Violet’s case, there were times I would have someone bring the models over to me while operating just for me to take a look from different angles, to get my bearings in terms of where the orbit was, where the optic nerve was,” he said. “You might be making a bone cut that is five millimeters away from a fairly important anatomic structure, so it’s nice to have someone be able to spin that around in front of you to get a much clearer 3-D image in your head of what you need to do on the patient.”

As general surgery and the surgical subspecialties continue to move toward minimally invasive techniques and as these procedures become more sought after by patients, surgeons are facing new challenges that can be alleviated, in part, through 3-D modeling. “With the rising demand for minimally invasive procedures, surgeons are no longer able to fillet open the anatomy and see everything they need to,” said Dr. Woo. “Frequently, you are looking at the anatomy through a very tiny incision or through an unusual angle and with a limited view of what exactly is going on. With a 3-D model on hand, it really helps the surgeon get his or her bearings by having a millimeter-to-millimeter exact correlation from model to patient.” These models can also be sterilized so that the surgeon can manipulate the model on the operative field while performing the procedure.

Surgical education and training benefits

For surgeons—whether the user is an experienced surgeon, a resident, or a medical student—there is no replacement for the knowledge afforded by holding a solid object and understanding its nuances.

“We are a major teaching center, and education and training are typically at the core of what we do,” said Amar Singh, MD, FACS, a urologist with Erlanger Health System, Chattanooga, TN. “A very useful part of resident education is having [trainees] hold a model in their hands and look at the 3-D contour of the tumor and consider how they can approach it surgically.” Surgeons who have done thousands of organ-preserving kidney operations, for example, know the pitfalls of the procedure, “and communicating that knowledge base to a resident is so much easier when you have something tangible,” Dr. Singh said.

In a panel session titled Emerging Technologies in Simulation presented at the ninth annual meeting of the Consortium of ACS-Accredited Education Institutes (ACS-AEI) in March 2016, Robert Sweet, MD, FACS, executive director of the Institute for Simulation Healthcare (formerly the Institute for Simulation and Interprofessional Studies), University of Washington, Seattle, underscored the pedagogic benefits of 3-D printing technology, particularly for resident education. “You can do these cases that you might not normally see during residency [with 3-D printed models],” said Dr. Sweet, a professor of urology. “If we’re going to credential people to do things that they’ve never seen, that’s problematic. 3-D printing offers us the ability to essentially immortalize these rare cases and create a library of opportunities for students for things that they might see during their residency or training program.”

Katherine A. Barsness, MD, MSCi, FACS, pediatric surgeon; director, surgical simulation at Ann and Robert H. Lurie Children’s Hospital of Chicago; and associate professor of surgery and medical education, Northwestern University Feinberg School of Medicine, Chicago, IL, said she has been using 3-D printers at Northwestern Simulation since 2011 to create new tools to train surgeons in her specialty.⁷ Dr. Barsness also spoke at the ACS-AEI Emerging Technologies in Simulation panel session on the topic of hybrid simulation—the use of surgically modified real tissue placed into 3-D printed thoracic and abdominal cavities. In an interview, Dr. Barsness said, “Specifically, it started in pediatric surgery. It was used to work with the size limitations inherent to neonatal surgery—when you’re trying to simulate that small space, 3-D printing is the most accurate way we’re able to do that. It has allowed us to create size-appropriate, anatomically correct teaching aids, so that no longer is a newborn infant exposed to the risk of the learning curve; rather, the learning curve is borne on the back of the simulation,” which is especially meaningful with the fragile tissue at play in neonates.

The educational and training benefits of the technology also extend to experienced surgeons. “There’s a technology called flow diversion, which is used to treat complex brain aneurysms. There are physicians who have done a few cases as a part of their training, but the condition is relatively rare,” Dr. Siddiqui said. To enhance their understanding of the condition, he and his colleagues at The Jacobs Institute have developed an advanced users course, in which physicians from all over the world fly into Buffalo and spend a couple of days at the institute watching surgeons perform live demonstrations of complex cases. “Then we 3-D print some of those cases and have the physicians practice on the 3-D models to gain a stronger familiarity with what they will have to do to be successful with those procedures on patients,” he said.

The ability to customize a 3-D printed model also is a useful feature, Dr. Siddiqui noted. “If you have a patient with a perfect aneurysm that would be great for training, you print out that model, and then it can be easily modified in the future to include different complications,” he said. “A bend here, an additional aneurysm there—you can represent any additional problem you want to a student, fellow, or even yourself, in order to work in a variety of training scenarios. That’s a unique advantage of how this all gets done.”

Quality metrics as a key to reimbursement

While 3-D modeling is beneficial in the areas of education and training, the measurable value of 3-D modeling on improved surgical outcomes is yet to be determined. However, anecdotal evidence suggests this technology can reduce the risk for complications and lessen the time the patient spends under anesthesia.

“We’ve done some early work showing a decrease in OR times as a result of the models,” Dr. Meara said. “If you can cut an hour off a 10-hour case, each hour in the OR is extremely expensive, so maybe a $500 or $800 model is not terribly expensive if you are cutting an hour or an hour-and-a-half of OR time,” he said, adding that he was able to save approximately one to two hours on Violet’s case because he had a clearer idea what he and the surgical team were going to do in the OR. So while the infrastructure costs in acquiring an on-site 3-D printer are considerable—the high-quality model at Boston Children’s Hospital costs $400,000, and printers in use at other hospitals can run upward of $100,000—with efficient use, the technology has the potential to save money over time.¹

A pilot study—reportedly the first in the world to review 3-D modeling in a hospitalwide setting—was launched by the Erlanger Health System in October 2015, to examine how 3-D printing can be used to improve surgical outcomes and the challenges—including costs—involved in using this technology in a large public hospital system.^8,9 The study was conducted in partnership with the University of Tennessee College of Medicine-Chattanooga and 3D Operations, Inc. (3D Ops), a provider of patient-specific 3-D printed models.

“During the first six months [of the study] we are trying to figure out how to create these models accurately and what is the most cost-effective way to do this so that every surgeon has access [to this technology],” said Christopher Keel, DO, a urologic surgeon, Associate Member of the ACS, and the first surgeon at Erlanger to use a 3-D model for surgical planning.¹⁰ To prepare for that operation, which involved a kidney with multiple large tumors, a model was created using a 3-D printer that costs approximately $250,000, including software.

“We are doing this in a research setting in collaboration with industry because there is no reimbursement currently for 3-D printed models,” explained Dr. Singh. “We do believe this technology helps us provide better outcomes, but there is no way to quantitate that in dollars and cents right now. If I am a hospital or health system or university, unless there is a grant or philanthropic money, it might not make sense to purchase a high-end printer. This is an extremely dynamic technology—the printers that are out there could be outdated within the next two years. However, you do see situations where organizations are leasing the technology and equipment or partnering with another entity,” said Dr. Singh.

Drs. Singh and Keel emphasized the importance of quality metrics as a key to reimbursement, particularly if 3-D printing technology can be linked to better outcomes and enhanced efficiency.

Hurdles to adoption

At least three primary limitations are associated with 3-D printing technology for use in surgical models—slow build times, a lack of autonomy, and expensive equipment and software costs. Build times for a single model can last from a few hours to an entire day and can vary depending on whether the 3-D printer is housed on-site or with an outside company. “Speed is one of the things that developers are currently working on,” Dr. Keel said. “It depends on the type of organ you are printing. They’ve printed a whole brain before, and obviously, that takes more time than it does to print a kidney, particularly if it’s a smaller kidney.”

Another challenge to wide adoption of 3-D printing is the training involved in mastering the scan conversion software; as a result, surgeons must typically rely on experts in printer technology to generate models.¹¹ “A lot of these printers need babysitters to sit and watch as they are printing because there can be errors [or because] you have to switch out the materials,” Dr. Sweet said.

“The reality is that there is a huge amount of infrastructure that needs to be developed [by a hospital] before the first case,” Dr. Woo added. “Not only do you need to have a 3-D printer available, which is a significant cost in and of itself, you also need the technical expertise to be able to manipulate the data in order to create the model that you want, and generally that’s not something that surgeons can do themselves.”

Furthermore, medical-grade printers are expensive and cover a range of price points. According to Dr. Sweet, high-end 3-D printers can cost up to $850,000 depending on the scale, number of inks, and performance capabilities of the device. At the low end of the market, namely the consumer market, 3-D printers sell for as low as $140. “Most of the market right now is either on the low end or the high end, but what’s interesting is the merging [of the two markets] right in the middle,” said Dr. Sweet. “This emerging middle market is where you are getting some of the capabilities of the high-end machines, but with lower costs driven by scale and so on, and this is what we need.”

“You don’t necessarily need the most expensive printer to do what we want to do, although the higher-grade printers have much higher resolution and have more flexibility and allow you to use not just one material but multiple materials,” said Dr. Woo. “I can mix a plastic type of material with a rubber material and find the perfect mix so that we are able to get the texture or the flexibility in the material that we want to allow us to achieve our goals.”

Future applications

Although 3-D printing already has affected surgical practice and training, the technology has even greater potential going forward. The future of 3-D printing in health care will likely revolve around bio-printing, which entails creating biological structures through a layered manufacturing method, similar to the one used today, but instead of using a resin polymer, bio-printing uses a stem cell base—tissue grown in a lab. “That is the next step in evolution. We might even see both those types of models merge together,” according to Dr. Singh.

Work already is under way to merge the field of artificial materials and biologics in 3-D printing, Dr. Sweet said, through the use of advanced inks and embedded sensor technology. “When you’re dealing with electronics, they’re two dimensional, they’re hard, rigid, and brittle, and they have very high processing temperatures from a manufacturing standpoint, where biological structures are three dimensional, soft, flexible, stretchable, and are temperature-sensitive,” he said. “So what is nice about 3-D printing is that it can actually solve both those problems and you can start embedding electronics with biological structures.”

Intertwining organic and inorganic materials also may create new possibilities in functional human tissue and organ generation. “There is a core printing and a shell around it, and what you can actually do is implant drugs, small growth factors, and those can be activated and released when you want them to be released using laser or mechanical energy,” Dr. Sweet added. “So imagine that—imagine being able to print an organ with little beads of growth factors embedded in it that may be released over time slowly or when you activate them for release. This opens a whole new world for us, not only in training, but for organ replacement and healing as well.”

The usability of 3-D printed materials inside patients is still in its early stages, but surgeons already are considering the potential. “I guarantee you that someday, you will be able to print 3-D pieces of, for example, orbital bones, which you’ll be able to feed stem cells into and have it turn into bone,” Dr. Meara said.

Dr. Siddiqui believes that the ability to print functional organic components would be a benefit to vascular surgery. “In vascular surgery, we’re always looking for the best grafts, whether that is a radial artery graft, or a saphenous vein graft, or a cephalic vein, or an internal mammary artery—it’s a perpetual issue with trying to the find the right graft, the right diameter, with properties that will allow it to serve as an effective conduit and not cause spasms,” he said. “Being able to print artificial vessels would be a major step forward in any vascular surgery.”

Ultimately, the goal is to one day be able to print entire functional organs for use in human transplantation; these organs, created from a patient’s stem cells, could avert the need for immunosuppressive drugs and alleviate the ever-growing need for donor organs.¹² Achieving that aim is years away. The complexity of replicating a biologically viable liver or heart via 3-D printing is beyond the current scope of the technology, but the science is continuously improving.

As the capabilities of 3-D technology advance and lead to improved patient safety and outcomes, the surgeons interviewed for this article predict that 3-D printers will be as common in hospitals as CT scans within a decade. “It’s the same thing I told a medical student last week,” said Dr. Singh. “I’ve been in practice for nine years, and I don’t do a single operation the same way I did nine years ago. The ultimate goal is to provide equivalent or superior care and outcomes for your patients and minimize their complications, and if you have a technology that is affordable or that will become affordable as it continues to be developed, you can resist it all you want, but the wave is going to sweep over you, and we have seen that with every sort of minimally invasive approach.”

“There are some incredible benefits of this technology for the surgeons who are willing to get out of their comfort zone,” Dr. Woo added. “I firmly believe that 3-D printing is here to stay and it’s actually going to revolutionize not just the practice of surgery, but really the practice of medicine.”

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References

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