Three-dimensional printing modeling: application in maxillofacial and hand fractures and resident training
Imaging techniques in reconstructive surgery are of great assistance not only in diagnosis but also in preoperative planning; however, they are often limited to interpreting three-dimensional structures on flat surfaces. Three-dimensional (3D) printing has made it possible to overcome these limitations by allowing the creation of customized 3D anatomical models. We set out to create 3D printed models to demonstrate its application in maxillofacial and hand fractures and resident training.
Ten patients with hand and craniofacial fractures of different types were studied. Computed tomography was performed; the image files were processed digitally, and 3D models were subsequently printed. The quality and accuracy of the obtained models were rigorously evaluated, and the models were then used by plastic surgery teachers and residents in the preoperative planning.
The comparative measurements confirmed that the models are at real scale with a 1:1 ratio; the pre-cast osteosynthesis plates were perfectly matched to the patient’s anatomy intraoperatively, and the lengths of the pre-selected screws were accurate. The anesthetic surgical time was reduced by 20%. Teachers and residents were satisfied with the use of models for clinical discussions of patients and for preoperative planning and the advantages of manipulating physical models were highlighted.
We have created low-cost, good quality, reliable, and accurate 3D printed models for the preoperative planning of reconstructive surgeries of maxillofacial and hand fractures, reducing the operative times and providing a new academic teaching tool in the training of residents of plastic surgery.
Level of Evidence: Level IV, therapeutic study.
KeywordsThree-dimensional printing Computer-assisted surgery Plastic surgery Maxillofacial injuries Fracture fixation Hand injuries
Within plastic surgery, the main objective of reconstructive surgery is to restore or improve morphology that determines the physical appearance and function of abnormal areas of the body that have been altered by various lesions or pathologies in congenital or acquired forms. Reaching the objectives proposed for a complex reconstruction often translates into great technical difficulty, demanding skills and abilities that represent a real challenge for the acting plastic surgeon, who very often performs preoperative planning in which photographic documentation and paraclinical images are studied, which are very helpful not only in diagnosing but also in planning the surgical strategies to be executed for each patient in an individualized manner.
Traditionally, the assessment of patients with maxillofacial fractures, hand fractures, deformities, and tumors includes imaging studies such as conventional X-rays, computed tomography, magnetic resonance, and other technologies. The passage of time and a series of great advances have made it possible to improve the resolution of the images obtained, giving the doctor an increasingly close-fitting visual reality of the patient that is easy to interpret. Initially, only low-resolution images in a two-dimensional plane obtained with X-rays were possible; however, today, the resolution achieved and the possibility of obtaining three-dimensional (3D) images have made these methods almost indispensable tools in diagnostic evaluation, in planning, and in the execution of the treatment of this type of patient. However, they still have the limitation of being represented on a two-dimensional surface or on a flat screen and they are sometimes insufficient for obtaining detailed perceptions of complex anatomical structures [1, 2].
The ever-growing science of innovation and constant advances have allowed us to go a step further, achieving the realization of design images for the creation of 3D physical objects in a range of unimaginable applications. The applicability in medicine has been quickly investigated and applied with wonderful results, with the creation of real anatomical models that not only provide the most visual information but also allow dynamic interaction with a real-scale physical model of the patient’s anatomical structures .The most innovative technique oriented in this field is represented by 3D printing. The birth of this revolutionary technology has its beginnings in 1988 , when Chuck Hall, inspired by existing inkjet printers, created the stereolithography apparatus (SLA) coined by its creator and patented on that date ; two years later, he founded the company 3D Systems and began to market the first 3D printers in the world.
The stereolithography patent prompted the development of new printing methods, faster and cheaper, such as printing by depositing liquid material (fused deposition modeling; FDM) created by Scott Crum in 1990 ; other more complex and expensive technologies include selective laser sintering (SLS), electron beam melting (EBM), selective head sintering (SHS), binder projection (direct shell production casting; DSPC), and laminated object manufacturing (LOM), to mention the best known, thus expanding the variety of techniques for creating 3D models. However, it was not until 2009 that the expiration of the FDM technology patent  generated a global commercial explosion, with the manufacture of printers of different models at very accessible costs.
Currently, the most commonly used 3D printing technologies or rapid prototyping, as they are also known, are stereolithography and FDM. The FDM has been very advantageous for providing greater accuracy, faster printing, and lower cost. At present, an increase in accessibility, a decrease in processing times, and a decrease in costs have resulted in an increase in the use of rapid prototyping technologies in the medical field.
Stereolithography is usually expensive; the cost of photo-curable resin ranges from 80 to 100 dollars per liter, and the price of the equipment exceeds 80,000 US dollars. The high costs of the equipment and the materials in the manufacturing process have made this technology poorly accessible and scarce in our environment.
Three-dimensional printers using FDM technology work by melting the input, which is a strand of 3- or 1.75-mm filament and may be from different materials and colors. The most widely used materials are ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid); however, there are other materials on the market, such as polycarbonate, PCL (polycaprolactone), PPSU (polyphenylsulfone), PEI (polyetherimide), PVA (polyvinyl acetate), and nylon, among others. The filament is pushed through a hot nozzle, producing a small melted plastic thread that is deposited on the machine platform in cross-sectional layers, from layer to layer, until the piece is created. This type of technology is very low cost and, based on quality, it can vary between 500 and 3500 US dollars [8, 9], which makes it accessible to virtually anyone, allowing 3D printing to be brought into homes and offices.
Three-dimensional printing uses computer-aided virtual design plans (computer-assisted design or CAD) or 3D image files as guides for printing; the tomographic images are stored in DICOM (Digital Imaging and Communication in Medicine) format and contain information of both bone and soft tissue volumes so that they can be analyzed digitally by selecting the desired structures, cleaning artifacts, and creating a final piece that is stored in STL (STereoLithography) format. The standard interface data between CAD software and the printer are in STL format. An STL file contains visual information in three dimensions, allowing it to be recognized by the printer and to perform the printing of the model (computer-assisted modeling or CAM). To print, the machine reads the file and establishes successive layers of material that must be deposited to construct the model from a series of cross-sections. The main advantage of this technique is its capacity to create almost any geometric shape. The resolution of a 3D printer is described by the thickness of the layer and the X-Y resolution in dpi (dots per inch). The average thickness of each layer is 0.1 mm (100 μm), although some machines can print layers as thin as 16 μm (0.016 mm) .
The use of 3D printing in medicine is gaining more ground. The increase of scientific publications on the use of this technology applied to the different branches of medicine, especially in surgical specialties, has proved to be very useful and advantageous. The aim of this study is to evaluate the applicability of 3D printed models obtained with FDM technology in different areas of plastic surgery as well as its contributions to the training of residents.
Materials and methods
Classification of patients by age, gender, and type of fracture
Ages between 18 and 25
Ages between 26 and 35
Ages up to 36
In mandibular fractures, the models, by simulating the surgical process, allowed for the pre-casting of titanium plates to be adapted to the patient’s anatomy and for the selection of the accurate type and length of each screw according to the thickness of the cortical bone.
In orbital fractures, besides the aforementioned, the models allowed for the direct visualization of the bone defects of the orbital walls, as well as the actual size, shape, and exact location. Furthermore, the pre-casting of the titanium mesh used to repair these bone defects made the surgery much easier, given that the manipulation of the mesh in the models is much better than the manipulation of the mesh in the patient, where the soft tissues interfere with the process. The printing of a model “mirroring” the healthy orbit allowed for the creation of a practically exact model of the orbit before fracture, which resulted in an exact pre-casting of the mesh with lower morbidity.
In carpal fractures, the models allowed for the detail evaluation of the characteristics of the fracture lines and its relation with the adjacent bones. Besides, models made it possible for the preoperative calculation of the type of osteosynthesis screw to be used, its length and direction, minimizing error possibilities in intraoperative calculation.
In pseudarthrosis of scaphoid bone, 3D models allowed for the planning of the bone fragment reduction and the characteristics of the required bone graft, for its size and shape, which resulted in an exact adjustment to the defect (Figs. 6 and 7).
The 3D haptic modeling have made it possible to take a giant leap in the evaluation of patients with maxillofacial and hand fractures, providing not only visual but also tactile information and allowing dynamic interaction with a real-scale physical model of the anatomical structures of the patient . Stereolithographic models have been widely used in the planning of surgeries. The advantages of these models have been widely disseminated, as they are very useful in the diagnosis and treatment planning [4, 11, 12, 13].
Three-dimensional printing technology has emerged in medicine; it includes the printing of organs [14, 15, 16, 17], body parts [18, 19], custom implants [20, 21, 22, 23], and prosthetics [24, 25, 26]. In plastic surgery, these tools offer various prospective applications, including 3D preoperative models for surgical planning and student’s education and training [27, 28]. Researchers from various surgical disciplines have demonstrated the usefulness of 3D printing in academic training, such as in neurosurgery [29, 30, 31], cardiothoracic surgery [32, 33], urology [34, 35], and general surgery .
Computer-assisted surgical planning, combined with patient-specific surgical guides, is a very powerful technology that has the potential of improving the accuracy and consistency of orthopedic surgery, for example, in performing osteotomies for malunited upper extremity fractures. The use of patient-specific surgical guides allows the surgeon to perform precise and relatively easy corrective osteotomies techniques that result in satisfactory clinical outcomes [37, 38, 39, 40, 41, 42, 43, 44, 45, 46].
The maxillofacial surgery is perhaps the one that has benefited the most from this technology; its applications seem to have become broader and broader, ranging from simple anatomic models to patient-specific implants (PSIs), including cutting or drilling guides. Since the first publication of Mankovich et al. in 1990 reporting the possible use of 3D-printing to make anatomic models in maxillofacial surgery , a great number of teams have published articles on the clinical use of this technology all around the world. The main indications are for dental implant surgery, mandibular reconstruction , orthognathic surgery, and craniofacial reconstruction [21, 49]. Concerning dental implant surgery, the most printed 3D objects are surgical guides designed to facilitate the orientation and execution of drillings, allowing a correct implant placement, as predicted in the preoperative planning. Concerning mandibular reconstruction, the most printed 3D objects are surgical guides .
A recent review by Gerstle et al. on three-dimensional printing and plastic surgery applications divided the uses into three categories: (1) surgery planning, (2) patient and resident education, and (3) custom prosthetic development .
Jacobs et al. did a systematic review of three-dimensional printing articles for patient-specific craniomaxillofacial surgery, and they found out that the analysis of direct surgical applications revealed four major classifications of increasing three-dimensional printing complexity: type I: contour models, type II: guides, type III: splints, and type IV: implants .
Contour models represent patient-specific anatomy that is three-dimensionally printed and used as an exact replica of the patient’s bone anatomy for contouring of hardware, such as titanium plates, which is easier to manipulate on a model than intraoperatively, where the structures are obstructed by soft tissue and bleeding. Therefore, contour models represent the positive space models where the patient’s imaged anatomy is recreated in the three-dimensionally printed object.
Guides use the negative space surrounding a patient’s bony anatomy to print patient-specific templates that fit only for certain segments of the bone, used intraoperatively to guide precise cutting or drilling. Whereas guides are replicas of actual patient structures, splints are defined as replicas of virtual final postoperative positions of patient structures, most often used in splinting of final dental occlusion in jaw operations. Although splints are also negative space models, based on a virtual final position that does not yet exist, they require advanced three-dimensional design software to perform a virtual “surgery” simulating the final situation.
Lastly, implants are defined as three-dimensionally printed objects directly implanted into the patient, or as a three-dimensionally printed object used as a cast for pourable implant material . According to this classification, all of our cases are type I: contour models.
The advent of new 3D printing technologies such as FDM have enabled rapid prototyping at a lower cost, providing a simple and easy-to-use system that uses layered deposition of liquid plastic filaments such as ABS and PLA to obtain pieces of excellent quality. The accuracy of this type of 3D printing is dependent on several factors, such as the quality of the image of the STL file, which in our case stems from the quality and resolution of the tomographic image; another factor is the specifications of the printer used and its calibration. Most modern FDM printers allow 0.1-mm-thick layers; however, vibrations caused by the movement of the printer during operation prevent the prints from actually reaching that thickness, usually being limited to 0.5 mm . We have achieved high-quality prints with a thickness of 0.6 mm using a low-budget printer.
An increasing number of research studies are currently being published worldwide citing the use of this technology [53, 54, 55, 56, 57, 58, 59, 60, 61]. At 2015, a study using FDM technology to recreate bone fractures in traumatology was published in Italy by Bizzotto . The results were very similar to ours regarding the advantages of this new technique in preoperative planning and in education.
It is well-known that surgery time is closely related to the risks of complications arising from anesthesia, bleeding, infections, and postoperative complications. One of our objectives has been to reduce anesthetic surgical time in these surgeries; plate casting, cortical bone measurements, and screw selection consume much of the surgical time, and the time spent on these activities depends directly on the complexity of the fracture and the surgeon’s abilities. Therefore, performing these steps preoperatively using rapid prototyping models shortens the surgery time; some authors have demonstrated a significant reduction of the time spent in the operating room by using this technique. Lethaus et al. achieved a reduction of 0.4 h in the surgical time of mandibular reconstructions with free flaps , whereas Hanasono et al. reported a reduction of up to 1.4 h using rapid prototyping models in the preoperative planning of mandibular reconstructions . Liu et al. reported an average reduction of 2 h when compared to conventional surgery . In our study, we achieved a reduction of 20% in surgical time. We prefer to express this reduction as a percentage since in the academic field, where the majority of cases are operated by residents in the full learning curve, the surgical times can vary significantly from one surgery to another, depending on the experience and skills of the treating surgeon.
The 3D models created with FDM technology printers are high-quality, reliable, accurate, and low-cost models that can be successfully used as guides in the preoperative planning of complex surgical treatments, reducing the anesthetic surgical times, optimizing treatment outcomes, and improving patients’ understanding of the pathology. It is concluded that the three-dimensional printing surgery techniques herein reviewed are especially advantageous for improving outcomes in plastic surgery techniques, such as maxillofacial and hand surgery, greatly contributing to the academic education of the residents in the training period.
Compliance with ethical standards
Conflict of interest
Jacobo Oscar, Giachero Virginia, Hartwig Denisse, and Mantrana Gustavo declare that they have no conflict of interest.
All procedures in studies involving human participants were performed in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. For this type of retrospective study formal consent from a local ethics committee is not required.
Informed consent was obtained from all individual participants included in the study.
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