Point-of-care three-dimensional printing for craniomaxillofacial trauma

Off-site CAD/CAM vs. point-of-care 3D printing

Most of the literature discussing CAD/CAM principles and 3D printing for the treatment of acute facial trauma is related to orbital trauma^[19]. This was an excellent starting point because of the predictability of model fabrication. That is, a mirror image of a non-injured facial skeleton serves as an excellent template to build upon. It was not until recently, however, that studies started to emerge demonstrating the use of CAD/CAM principles with custom milled and/or pre-bent plates for mandibular or complex facial trauma^[14,20-24]. Currently, these investigations generally follow two distinct paths. A surgeon can either complete the workflow via a third party (i.e., outsource) or choose to keep the process in-house. Each method has its own pro and cons.

First, we consider the outsourced, third-party workflow [Table 1]. This was excellently detailed by Kokosis et al.^[14] in 2018 in a series of five cases. When a patient is injured, the CT scan used to diagnose the injuries must be uploaded to the portal of the company providing the VSP services. This is surgeon and/or institution dependent. Examples include Synthes ProPlan CMF, KLS Martin IPS, and Stryker 3D Systems VSP. Once the DICOM data (i.e., files from the CT scan) are uploaded, the images and files are reviewed by clinical engineers using the company’s proprietary software. The data are then processed, i.e., the CT images are segmented. Simply put, this means the areas of interest from the CT data are isolated. For example, the mandible could be segmented from the rest of craniofacial skeleton to make data processing easier. At the surgeon’s convenience, a “go-to-meeting” online VSP session is completed with the clinical engineers. During this meeting, manipulation of the fractures occurs, and a decision is made upon the design of a custom reconstruction bone plate. The third-party clinical engineers check the manufacturability of the custom reconstruction plate. Once the internal checks have been completed by the third party, the virtual case plan is finalized by the clinical engineer and an approval is sent to the surgeon. Once the surgeon approves the plan, the custom reconstruction plate is milled from a titanium block. Once the plate fabrication is completed, it is shipped to the surgeon. The first major advantage of this workflow is the ability to have a custom-milled reconstruction plate. These plates have excellent adaptation and require no bending. The second advantage is the time of the surgeon is engaged in the workflow only during the VSP session and then the surgery. The disadvantage of this workflow is the amount of lead time required to complete all the required steps for plate fabrication and then, obviously, the amount of time required for manufacturing and shipment. This workflow from start to finish is approximately 6-7 days^[14]. In the authors’ experience, this timeline may not be available to all surgeons. One could expect a timeframe of 10-14 days from date of injury to plate arrival, assuming the CT scan is uploaded soon after initial completion. This timeframe could be applicable to patients who are admitted, such as a poly-trauma patient with concurrent mandibular or craniofacial trauma. Many of these patients have overriding issues that make this 1-2-week timeframe feasible. However, in many, and indeed often the most acute facial trauma cases, the 1-2-week timeframe is less than ideal.

Considering the price of 3D printers is continuing to drop, for example, the MSRP of a FormLabs Form3 printer is approximately $3000, and the learning curve of the CAD/CAM programs is becoming flatter, many surgeons and institutions are turning to point-of-care (POC) manufacturing^[25]. POC manufacturing refers to the “just-in-time” creation of anatomic models or other items at the place of care, such as the hospital or clinic^[25]. POC or in-house 3D printing and manufacturing provide cost-effective CAD/CAM technologies in the delivery of services that otherwise would not be feasible due to, at least in part, the high cost of third-party VSP sessions and manufactured products and the lead time required for these services/products^[25]. Several great examples of surgeon-led in-house manufacturing techniques are starting to emerge within the literature^[21-24,26]. Furthermore, in-house 3D printing has been demonstrated to decrease operative time^[22].

The workflow established by the authors at the University of Louisville (Louisville, KY, USA) is described below [Figure 2]. This workflow is designed for expedited in-house CAD/CAM methods to fit the ideal treatment timeframe for acute craniomaxillofacial trauma^[24]. This technique merges the benefits of having an online VSP session with on-site 3D model fabrication for preoperative plate bending to virtually reduced mandible/craniomaxillofacial fractures. The first step is completed via image acquisition for diagnosis of the facial injuries. Ideally, this would be obtained using a fan beam medical grade CT scanner with 1.0-mm slices. After the initial surgical consultation, the DICOM files from the CT scanner are transferred to a compact disk. This allows for export to other computers. Ideally, cloud-based file sharing would be the most efficient process. The DICOM files are imported into the CAD software of choice. Our institution utilizes Mimics (Materialise, Leuven, Belgium) software. This is part of the Materialise innovation suite. Once the files are uploaded into the CAD software, segmentation of the data must be completed (see Marschall et al.^[24] for complete details). Segmentation is an essential process for image/data processing and many programs are available. Other examples include Anatomage MD design studio and D2P from 3D systems. Regardless of the CAD software utilized, the surgeon/institution much ensure they are FDA approved. An example of a free open-source software that is not FDA approved is 3D slicer. Once the segmentation of the mandible and each fracture is complete, virtual reduction is completed. In the authors’ protocol, this is completed via “virtual maxillomandibular fixation”. The teeth, and thus the fractured segments, are virtually placed into occlusion, which generally brings the bony segments into their correct pre-morbid position. Once this is completed, the condyles are examined to ensure they are appropriately placed within the Glenoid fossa. This is generally enough to rebuild the fractured mandible/facial skeleton in the computer. This may appear to be a technically challenging maneuver, but, in our experience, it takes a novice software user three runs through the workflow to gain competence. Once the operator is comfortable with this process, segmentation and virtual reduction can be completed within 10-35 min depending on the operator.

Figure 2. Louisville computer-aided facial trauma protocol.

After virtual reduction is completed, the new mandible is exported as a STL file which can be read by the 3D printing software. The printing software is dependent on the 3D printer used by the clinician. FormLabs printers use pre-form. Considering many 3D printers print using a platform that moves vertically out of a resin reservoir, supports must be added to the object, which is done in the software. Supports are important for 3D printing as they hold the model in place through the entire printing process. Although a clinician can use 3D printers that have slightly different working principles (SLA, FDM, DLP, etc.), that discussion is beyond the scope of this review. Once the object has been supported appropriately, printing can begin. The speed of printing is highly variable. For example, an inexpensive FormLabs (Somerville, MA) Form3 printer may take 5-6 h to print an entire mandible depending on resolution, while the NewPro (NewPro 3D Vancouver, British Columbia, Canada) NP1 can print an entire mandible in approximately 1 h. We use both of these printers in our workflow depending on the timeframe required. Once the print is completed, the model must be washed in isopropyl alcohol for approximately 15 min and then cured for 1 h.

Once the virtually reduced mandible has finished the curing process, it can be used as a template for reconstruction plate preoperative adaptation. There are several major advantages of preoperative plate adaptation. First, plate bending occurs out of the operating room, which can be as expensive as $100 per minute^[22]. Second, the plate bending can occur leisurely in the office or even at home. Last, the printed mandible can be held in the surgeon’s hand and examined in 3D. This model is not bound by soft tissues and visibility is not obstructed by bleeding or hemorrhage; this facilitates a truly unobstructed view. The fracture can be examined from aspects that cannot be truly appreciated during the operation or from reviewing the CT scan. Once the plate has been bent, it can be sterilized before surgery. Our current clinical experience demonstrated that most plates can be adapted in between 7 and 20 min when using this workflow. Obviously, the fractures can be approached via any method the surgeon chooses. The addition of a pre-bent plate, however, may make fractures that are difficult to treat via an intra oral approach more predictable, potentially saving the patient a cutaneous scar.

When comparing these two methods, one must also consider cost. Potentially high up-front costs are associated with the POC/in-house method. However, this is dependent on the equipment purchased. 3D printers can be as little as several hundred US dollars or hundreds of thousands of dollars. There is also variability in software costs. However, once these items have been purchased, the fixed costs of consumables are generally rather low. For example, a 3D-printed mandible using a resin-based SLA printer (i.e., FormLabs) costs approximately $7.00. Direct cost comparisons between in-house and outsourced methods are difficult to complete. Furthermore, depending on the contractual agreements between the hospital and company providing the CAD/CAM services, custom-milled plate costs can be different. Custom-milled plates can cost as much as $5000-$6000 (nearly double the costs of a Form3 printer). Added to this are the costs associated with model fabrication, planning session, etc. In our experience, the all-inclusive costs of a VSP, model fabrication, and custom-milled plate approach $10,000. When compared to a POC approach, stock reconstruction plates are approximately $1000. In the future, these techniques can be trained so that in-house technicians can complete the virtual reduction, decreasing surgeon time. Furthermore, in-house custom-milled plates can be fabricated in this same expedited manner.

In-house CAD/CAM case report

A 48-year-old male was assaulted causing bilateral mandibular fractures [Figure 3]. To assess the extent of his injuries, a standard maxillofacial CT scan using 1.5-mm cuts was completed in our university’s emergency department, whereupon the facial trauma service on call was consulted (it should be noted 1.0-mm cuts are preferred). After the consultation was complete, the DICOM files from the CT scanner were transferred to a compact disk and loaded onto our CAD/CAM computer within our 3D printing lab. The patient’s occlusion was reestablished virtually to aid in reduction of the fractures, essentially a virtual MMF. The mandible was then printed according to the protocol described above^[24]. Two locking reconstruction plates were preoperatively adapted to the 3D printed mandible. Once the patient was taken to the OR for definitive reconstruction, the fractures were all exposed in standard fashion. The mandibular bone was reduced, and the pre-bent mandibular reconstruction plates were applied with near perfect adaptation. The incisions were closed in standard fashion and a postoperative CT scan was ordered. The final result obtained was overlaid to our preoperative virtual plan to assess how accurately we executed the surgery using Geomagic Design X (3D Systems, Rock Hill, SC, USA). A root mean square value of 1.9 was obtained, with the highest variation occurring in sites where the reconstruction plate was applied. The patient went on to heal uneventfully.

Figure 3. Representative case. A 48-year-old male who suffered mandibular fractures: (A) preoperative CT scan; (B) (Left) segmentation of fractured mandible and (Right) virtual reduction of mandible; (C) 3D-printed reconstructed facial bones with preoperatively bent reconstruction plates; (D) transcervical approach to the mandible to expose both fractures; (E) postoperative CT; and (F) (Left) preoperative plan and (Right) heat map of merged postoperative result and preoperative plan. Areas cold in color (blue and green) represent areas of high accuracy, while areas of hot color (orange and red) represent areas of relative lower accuracy.