Editor’s note: This article is the second in a three-part series focused on novel technologies. The first installment appeared in the November issue, and the final article will appear in the January 2021.
Three-dimensional (3D) printing is defined as a process that builds 3D objects from a computer-aided model by successive addition of material layer by layer, in contrast to conventional forging, casting, or machining processes, in which material is poured into a mold and shaped by forceful impaction.
The 1980s saw the advent of 3D printers, which produced simple objects at high costs. In the four decades since its introduction, the complexity achieved by 3D printers has improved considerably, while the prices have dropped. These production methods are now used in a wide range of fields, including manufacturing, architecture, food, and medicine.
3D printing can be used to manufacture custom machine parts, auto bodies, firearms, airplane components, engines, and circuit boards. The heterogeneity of musculoskeletal anatomy and high cost of implant storage have led to the adoption of 3D printing within orthopaedic surgery.
The process of creating a 3D model in orthopaedic surgery typically begins with 3D imaging of bone, most commonly with CT. The image is then converted into a format recognized by the 3D printer software. The 3D printer then creates the 3D-printed model or implant layer by layer. Each 3D model can be made with a variety of materials, specifically chosen based on the intended application of the model; the most commonly used materials include ceramics and synthetic and natural polymers. For example, titanium is best used for implantation, and metals and bioceramics are best used for implants and bone restoration.
3D printing is now routinely used in orthopaedic surgery to print patient-specific anatomic models, implants, surgical instrumentation, external fixator splints, and surgical cutting guides. For example, surgeons use a patient’s two-dimensional images to create a personalized, 3D surgical plan. Surgeons can use these models to understand the often-complex 3D anatomy, especially in rare deformities and tumors, prior to surgery. The utility of preoperative 3D-printed templating was validated by a study comparing the surgical plans of residents who were given a 3D-rendered image versus a 3D-printed model. Residents who received the 3D-printed model had higher surgical plan scores compared to those who received the 3D-rendered image, demonstrating the potential value of 3D models for the education of patients, residents, and medical students.
As a second example of the use of 3D printing in orthopaedic surgery, consider that sarcomas of the calcaneus typically require below-knee amputation due to the difficulty in recreating a structural heel. In one study, orthopaedic surgeons created patient-specific 3D calcaneal replacements for tumors of the calcaneus. During 2.5 years of follow-up after surgery, patients’ CT results demonstrated no evidence of loosening or endoprosthesis failure, and both patients were satisfied with their functionality. Similar applications have been reported for surgery involving large tumors of the clavicle, scapula, and pelvis. 3D-printed implants can also be used to perform total talar replacement and delay or avoid hindfoot arthrodesis in patients with severe talar avascular necrosis that is not amenable to core decompression or vascularized grafts (Fig. 1).
Finally, 3D printing can be used to create patient-specific instruments designed to assist in guiding a saw or drill into a precise location for a specific patient. This method has been used in spinal surgery for pedicle screw insertion and for accurate placement of implants in total ankle, knee, and hip arthroplasty by application of the patient-specific instrument over its complementary bony topography, allowing for precise cuts.
At Rush University Medical Center in Chicago, an ongoing clinical study involves creating patient-specific 3D instruments for use in total shoulder arthroplasty (TSA). Accurate placement of the glenoid component remains a challenge in TSA and is highly predictive of wear patterns, implant failure, and stability. The study’s 3D-printed, patient-specific drill guides are theorized to improve the accuracy of glenoid positioning during TSA and subsequently lead to better patient outcomes.
Although 3D printing has ushered in a tremendous amount of excitement due to its potential contributions to surgical care, it is currently limited by a lack of long-term follow-up and pricing that remains cost-prohibitive for large studies. As 3D printing becomes more ubiquitous and less expensive, studies with well-powered sample sizes will be warranted to identify the true value of 3D printing versus predicate techniques.
The greatest potential advancements in 3D printing lie in tissue engineering and regenerative medicine. Tissue engineering is a growing field that aims to develop 3D printers with the function of creating biologically viable substitutes for living cells, growth factors, and other native human tissues or organs. The uses for such technology would be widespread, from reducing the need for animals in research to replacing damaged or diseased tissues in patients. Tissue engineering and its ability to allow for the production of complex tissues for patient-specific situations are promising.
However, bioprinting faces limitations and challenges. The first limitation in tissue engineering is the scarcity of biomaterials available for bioprinting. Scaffolds that are mechanically supportive and can maintain cell viability and function need to be developed for the field to continue to advance. Another critical challenge essential for long-term cell survival is vascularization. As the fields of bioengineering and bioprinting continue to develop, the ability to form vascular structures during the biomanufacturing process will become feasible.
Nasima Mehraban, MD, is a recent international medical graduate.
Daniel D. Bohl, MD, MPH, is a foot and ankle fellow at Baylor University Medical Center in Dallas. He is on the American Orthopaedic Foot & Ankle Society Research Committee and is devoted to furthering orthopaedic basic science and clinical outcomes research.
Stephen K. Jacobson, MD, is a foot and ankle orthopaedic surgeon at the University of Minnesota. He is a peer reviewer for the University of New Mexico Orthopaedic Research Journal.
Kamran S. Hamid, MD, MPH, FAAOS, is an orthopaedic surgeon specializing in sports ankle injuries and lower-extremity trauma at Loyola University Medical Center in Chicago. In his spare time, he is a musician, photographer, and startup company founder.
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