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    Examining Orthopaedic Applications for 3D Printing

    As the technology of 3D printing improves, it has the potential to revolutionize the practice of orthopaedic surgery. An institution’s investment in this technology, the authors say, can allow its surgeons to preoperatively plan complex cases, develop implant designs, and enhance education of residents and fellows.

    Authors

    Jonathan Vigdorchik, MD, and Stephen Yu, MD

    Disclosures

    The authors have no disclosures relevant to this article.

    Introduction

    Three-dimensional (3D) printing technology has recently been introduced in medicine, with promising applications in nearly every specialty [1] including orthopaedic surgery. A range of clinical applications are undergoing extensive research and development.

    What Is 3D Printing?

    3D printing utilizes a unique manufacturing process from concept to real-world design. Thr an additive manufacturing process, a product is engineered de-novo using a wide array of materials.

    Traditionally, products have been fabricated using raw materials in a subtractive manner through machining processes, such as Computer Numerical Control (CNC) and Mill/Lathe machining. CNC manufacturing is advantageous in that its creations can be reliably produced with a high degree of tolerance.

    However, there are limitations to the subtractive manufacturing, including physical impediments in the design process. While there are effective solutions to this in the engineering world, often in medicine, biomaterials and complex anatomic designs are difficult to effectively replicate through subtractive manufacturing, especially on the micro scale.

    To fabricate a 3D-printed model, a concept must first be developed through drafting. Typically, computer-aided design (CAD) software is utilized to create a 3D geometric model. Next, the material(s) must be selected based on availability, workability, and cost.

    Several different types of 3D printers are available, and the application dictates which type of printer should be utilized. At present, Fused Deposition Modeling (FDM), stereolithography, and other additive manufacturing techniques are the major workhorses of 3D printing for medical applications.

    FDM is one of the earliest and the most basic 3D printing technologies, and it involves the melting of thermoplastics through a heated nozzle, quite analogous to glue gun technology. The nozzle deposits the material layer by layer, with no curing process required; the newly layered thermoplastic hardens and integrates itself into the previous material or scaffold. Other 3D printing processes may require a curing stage with an external energy source, such as UV light, lasers, or electron beams.

    Orthopaedic research laboratories currently utilize the FDM printing method for rapid prototyping and end-use product printing. It is well suited for applications in which plastic materials can be used, such as for fabricating parts for biomechanical testing or for creating custom saw guides.

    After a CAD design is imported and the desired materials are loaded, the 3D printer can output a product in less than a day. Some post-processing is usually required, such as removal of scaffolding or additional machining. Once finished, the 3D-printed product can be ready for immediate use, whether it is a prototype or an end-use product.

    3D printers are capable of printing a wide array of materials, from cobalt chrome and titanium to different forms of plastics. Some recently developed printers are capable of printing biomaterials, such as live bone tissue and soft-tissue scaffolds, thus broadening the applicability of 3D printing.

    As modern 3D printers become more compatible with materials relevant to orthopaedics, the integration of this technology into the field of orthopaedic surgery will only grow.

    Applying 3D Printing to Orthopaedic

    There are numerous examples of how orthopaedic surgery currently employs 3D printing technology. Some of the first orthopaedic innovations were large-scale designs that were still highly patient specific and fully customizable, such as fracture-specific casts and custom-fitted prosthetics.

    The concept of a fracture-specific cast is based on creating a predetermined mold that offers optimum stabilization for a case-specific fracture pattern. Customized 3D-printed prosthetics have been popularized for practical and creative reasons. Amputee patients, for example, can receive affordable, personalized prosthetics in which the designer can add a limitless amount of creativity – such as a fully functional and sleek “Iron Man” arm for a child. [2] Previously, a prosthetic of this nature would have been significantly expensive and challenging to manufacture. 3D printing allows for unique and affordable solutions.

    In the preoperative and surgical planning of orthopaedic cases, 3D printing can be used to construct highly accurate, anatomic models from a patient’s radiographic studies (Figure 1). These anatomic models can be produced quickly and affordably, allowing for enhanced visualization and physical interaction that can improve appreciation of anatomy and enhance surgical planning. [3,4]

    Figure 1. A patient-specific cutting guide was fabricated to fit the exact contours of the tibia. This “true-fit” principle ensures accurate guide placement and saw cuts.

    This is especially advantageous for technically challenging cases, such as deranged anatomic variants or complex fracture patterns. [3,5,6] The surgeon will not only be able to visualize a true-to-life model, but he or she will also be able to simulate, practice, and adapt the surgical approach and techniques planned for the procedure. This can help any surgeon, from new trainees to experienced surgeons with complex cases. In addition, teaching models can be produced on demand and in quantity, on a case-specific basis (Figure 2). [7,8,9]

    Figure 2. A 3D model was created using computer software (above), which then communicates with a 3D printer to fabricate the product. An example of an anatomical model is brought to life using 3D printing technology (below).

    These teaching models can replicate bony anatomy to mimic actual anatomic variants, including fabrication of cortices and trabeculae, and they have material properties and a feel that is similar to live bone. In many ways, 3D printing of anatomic models offers vast improvements over sawbones and other models traditionally used in resident education.

    One of the greatest advantages of this technology is its broad utility in orthopaedic research. Basic science research, particularly biomechanical testing, can directly and indirectly benefit from 3D printing capabilities. For example, orthopaedic research laboratories have been successful in fabricating trabecular bone analogs, mimicking similar structure and biomechanical properties of real trabecular bone. [10]

    In addition, the fabrication of proper testing structures and instruments is integral to the success of a biomechanical study, and 3D printing makes the production, availability, and customizability of these components feasible. Whether it is creating a construct for testing or designing modular tray inserts to simulate alignment, 3D printing technology offers unique solutions to the procedural details and methodology of an experiment.

    Such applications with closer-to-life accuracy enhance the quality and repeatability of orthopaedic biomechanics and biomaterials research and help bridge the translation of laboratory to clinical practice.

    Although the field of orthopaedic surgery has just begun to benefit from the many capabilities offered by 3D printing technology, it is interesting to imagine what the next stages of development will bring.

    For example, highly customized implants, including fracture-specific plates, are currently in their early stages of development, [10,11] and in tandem with computer modeling and templating systems, can be fabricated in a reliable and cost-effective manner. A plate can be manufactured to fit the bony contours to provide maximum fixation of a reduced fracture. Moreover, the screw holes can be customized to minimize the working distance across the fracture site on a fracture pattern-specific basis. A construct of highly customized design may have the strongest benefit in complex fracture patterns, as standardized plating may not provide adequate fixation options or possess adequate contours, which may compromise fit.

    There is great interest in patient-specific joint reconstruction due to the advantages and evolved capabilities of modern 3D printing. Using the patient’s radiographic studies, a customized prosthesis – complete with fitted cutting guides – can be fabricated (Figure 3).

    Figure 3. Using a patient’s prior CT studies, a scapula was modeled for preoperative planning, surgical decision-making, and operative simulation. Multiple iterations of a model were easily produced.

    This concept aims to:

    • Simplify the surgical procedure
    • Save on the number of trays necessary for the case
    • Provide a “true” fit to patient-specific anatomy and individualized pathology

    Long-term clinical outcomes of patient-specific instrumentation/implants have yet to be established. However, recent studies suggest that patient-specific instrumentation/implants, in their current state of development, can be equivalent to outcomes of conventional implants and instrumentation [12,13].

    The drawbacks of previous patient-specific instrumentation/implants designs were related to the costs of radiographic imaging, manufacturing, and processing. The application of 3D printing technology to patient-specific instrumentation/implants may result in cost savings and increased operating room efficiency, which may be the rationale needed to eventually use this technology in total joint arthroplasty (TJA) on a more widespread basis. [14]

    3D printing can potentially benefit complex revision TJA cases as well: Highly customized augments and reconstructive acetabular cages could be fabricated for patients with extreme osteolysis and bone loss. The custom implants could be preoperatively fabricated to provide an “exact” fit to fill the defect.

    In addition, an osteo-inductive material could be integrated within a porous construct to accept and structuralize bone grafts and further stimulate and promote union.

    Historically, we have had the capabilities to create such implants. However, cost and practicality of the manufacturing process often hindered their use and development. With 3D printing gaining traction, research and development of these customized implants is much more feasible. [15,16]

    As technology and applications continue to evolve, 3D printers can be adapted to construct end-use products with live biologic tissue. For example, the ligament-bone and musculo-tendinous junctions represent particularly difficult structures to successfully repair. Further, soft tissue applications, such as meniscal transplantation, have structural and intraoperative fixation challenges that currently lack viable solutions.

    These ongoing challenges could potentially be addressed through additive manufacturing and enhanced scaffolding interfaces offered by 3D printing. [15-17] It is envisioned that a bone-tendon-bone soft tissue scaffold can be manufactured through 3D bioprinting using material grown from a patient’s host tissue. Further, with reverse MRI technology combined with advanced scaffolding interfaces, a true-to-size osteochondral plug could be fabricated and implanted into a host joint.

    Soft tissue applications will be a challenging endeavor; however the prospective clinical implications are promising. [17,18]

    Economic Benefit of 3D Printing Technology

    In today’s cost-conscious healthcare environment, 3D printing can deliver customized solutions in a time-efficient, reliable, and cost-effective manner.

    There are, of course, considerable start-up costs for 3D printing technology, including overhead and dedicated staff. However, ongoing maintenance and operation, along with the materials required to fabricate products, can be affordable and the benefits of 3D printing can be realized without creating significant economic burden.

    Institutions with academic, teaching, and research interests may gain the most from 3D printing. In addition, resident training programs can experience a benefit from the capabilities of 3D printing, including the ability to provide real-world surgery simulation and anatomic models to trainees and faculty that were once costly and difficult to obtain.

    In the future, once it has gained a more solid foundation and further integration in medical practice, 3D printing has the potential to successfully address clinical problems to a highly patient-specific degree while offering a unique, personalized approach that solves many issues specific to orthopaedic practice. Investment in this technology may improve clinical outcomes, ease the burden of technically challenging cases, and even increase patient satisfaction, all the while being time and cost effective.

    Implications and Ethics of 3D Printing

    Although 3D printing capabilities have been available for many years, the evolution of modern technology and the increased amount of information on the process has propelled 3D printing technology into a more prominent role in medical fabrication and applications.

    For the hobbyist, several websites provide instruction on manufacturing anything from furniture to guns and ammunition. A person can easily access these open source websites, find and download a design of his or her choice, and within a few hours, have a 3D-printed product ready for use. With the proper materials, individuals may even be able to manufacture their own pharmaceuticals and medical devices.

    3D printing is currently an unregulated environment with serious ethical implications. We must be careful about how this technology develops and integrates into medical practice. The NIH has established a public domain where medical professionals and laboratory technicians can share reliably accurate 3D printing files. [19]

    Use of 3D printing technology should also be introduced to medical treatment with caution, as no high-level evidence has shown the effectiveness of any existing 3D-printed medical applications. Although current applications are limited and may seem promising at this time, the full implementation of these devices needs to be supported with research and used with scrutiny. More research is needed to support the utilization of 3D printing in orthopaedic practice to demonstrate safety and efficacy.

    Conclusion

    3D printing technology has revolutionized design engineering in orthopaedic surgery. An institution’s investment in this technology can improve its surgeons’ ability to preoperatively plan complex cases, develop implant designs, and enhance trainee education.

    With technology evolving in every aspect of medicine, 3D printing continues to improve and diversify as it integrates into the field of orthopaedic surgery. Challenging clinical and academic problems can be addressed with low-cost and efficient production, offering a new perspective on solutions to these issues.

    Author Information

    Jonathan M. Vigdorchik, MD, is an Assistant Professor of Orthopaedic Surgery and Associate Fellowship Director in Adult Reconstruction at NYU Langone Medical Center’s Hospital for Joint Diseases, New York, New York. Stephen Yu, MD, is an adult reconstruction fellow at NYU Langone Medical Center’s Hospital for Joint Diseases, New York, New York.

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