The Halsted model of “See one, do one, teach one” forms the basis of most residency programs. Since the introduction of the Accreditation Council of Graduate Medical Education Outcome Project, many residency programs have looked into increasing the efficiency of residency training.1 Although the cadaver laboratory highlights the variabilities in human anatomy, the high cost of acquiring and handling cadavers makes it prohibitive to use cadavers for repeated and deliberate practice for skills acquisition.2,3 Thus, one common strategy is to use simulators in residency training outside of the operating room (OR) time.4-6
Current simulators range from simple polyvinyl chloride (PVC) pipes and rubber band constructs7 to realistic mannequins4,6 and highly accurate multimaterial three-dimensional (3D) printed simulators.7,8 In 2015, Lopez et al7 showed that the use of simulators improved the acquisition of surgical skills. With a simple PVC pipe and foam block setup, they found that medical students who trained on the simulator outperformed junior residents in many skill sets. Although a PVC-foam simulator may be able to aid the learning of tactile feedback, it does not present the actual anatomy. Thus, a learning gap still exists between working on the PVC pipes and performing surgery on a patient. On the other extreme, realistic mannequins are often too expensive to be used on a regular basis.4 Recent multimaterial 3D printing technology can create anatomic simulators with matching material properties, but it is still prohibitively expensive. Thus, currently, no effective way of creating low-cost anatomic simulators with high tactile fidelity exists.
Our goal was to develop economic and standardized training simulators and assessment tools for surgical training in residency training programs. Although the availability of cadavers and patient cases limits the exposure of residents, 3D printing enables residency program directors to implement a “standard” set of cases that their residents should be trained in and subsequently assessed on at the end of each year of residency.9 Developing an objective assessment of surgical competency is a challenging problem,4 and standardized simulators will help to eliminate at least one source of bias. 3D printing technology can potentially enable tactical training time outside of high-cost and high-risk OR time.
In this article, we present an economic 3D printed tactile hand simulator that provides both tactile and visual cues to bridge the gap between simulation and surgery. This tactile hand simulator was designed for percutaneous bone pinning of any of the phalanges and metacarpal bones. For a percutaneous procedure to be successful, the surgeon has to (1) locate the center of the bone to start drilling, (2) palpate the bones to target the correct plane of drilling, and (3) feel for the bicortical structure while drilling to track the depth and location of the pin. Challenges include slippage of the pin on the bone surface and controlling the drill to stay in the target plane.
Our tactile hand simulator was designed to enable all three steps to be performed to varying levels of difficulty. It has a soft gel layer over the rigid 3D printed skeleton to enable palpation of the bones to locate the center of bones and plane of drilling. Its 3D printed skeleton incorporates a bicortical structure to provide the tactile feedback, and initial trials showed slippage of pins on the bone surface. In addition to the three steps, our simulator has a transparent gel layer to provide additional visual feedback for junior residents. The transparent gel is covered by a removable opaque skin layer, and removing this skin layer reveals the skeleton. For junior residents, this visualization of the underlying bone structure informs them of the expected tactile feedback.
In this article, we also present the responses of a questionnaire study that solicits feedback from expert surgeons on the realism and expected usefulness of this simulator for residency training. Expert surgeons were each given a simulator and a questionnaire on the realism and effectiveness of our tactile hand simulator in residency training.
Tactical Hand Simulator
A tactical hand simulator is made using a combination of 3D printing and casting process. Similar to the clubfoot simulator described by Wu et al,10 the hand simulator is made of a 3D printed skeletal structure embedded in a ballistic gel matrix so that each bone piece is independently suspended in the gel.
First, the skeleton is refined from a computer-aided design (CAD) model of the hand to reflect a more realistic anatomy (alternatively, segmentations from CT images could be used) and exported as a surface shape model (ie, STL file format11). A fifth metacarpal bone fracture was included to provide context for the pinning exercise. The STL file is then postprocessed to insert links between bone pieces so that the skeleton can be printed as a single piece. 3D printing was done by our in-house 3D printing service. The skeleton was printed in white ABS plastic using a high-precision fused deposition modeling printer (Dimension 1200es; Stratasys) at a print resolution of 0.010″. A bicortical structure (cortical-cancellous-cortical) is incorporated in the 3D printed skeleton by specifying a 25% to 30% fill setting (sparse–low density). This setting generates an internal porosity that mimics cancellous bone.
The skeleton is then cast in the ballistic gel that mimics soft tissues. As suggested by Wu et al,10 the mold for casting ballistic gel is designed in CAD software (Blender; Blender Foundation) and printed on a stereolithography printer (Form2; Formlabs) using standard resin. This mold is made in several small sections because of constraints in print volume and to facilitate demolding. The 3D printed skeleton is then inserted into a 3D printed mold, and the ballistic gel is cast over the skeleton.
After cooling and demolding, a removable skin layer is created by brushing silicone over the ballistic gel and rotating the simulator to achieve a uniform thickness. The silicone used is pigmented silicone (Dragon Skin 10 and Fleshtone Silc Pig; Smooth-On) according to the manufacturer's instructions.12
Finally, the links between the bone pieces are broken to create independent pieces held in place by the gel. The simulator is thus able to support bony operations such as bone pinning, while featuring overall flexibility that facilitates palpation of the underlying bones.
The material cost of creating a hand simulator was approximately $150. The cost of 3D printing is based on the rate in our institute's in-house 3D printing service, which offers similar rates as bureaus for consumer 3D printing. Approximately 4 hours of postprocessing work after 3D printing is necessary to complete the simulator. The entire production time (including 3D printing time and other waiting time) is about 2 days. The cost is expected to be reduced markedly in the future as the cost of 3D printing continues to decrease. Economies of scale at mass production will also lower the unit cost of each simulator.
In a study to evaluate the hand simulator, five orthopedic surgeons were recruited as participants of the study. Inclusion criteria were age of at least 18 years, >5 years of experience in orthopaedics, and performance of percutaneous pinning of hand bones on a regular basis. Surgeons who were involved in the development of the phantom were excluded to eliminate bias.
All subjects were given a hand simulator and written instructions to perform transverse pinning of the second and third metacarpal bones, transverse pinning of the fifth and fourth metacarpal bones, and five additional transverse or intramedullary pinnings of the distal radius and at least one phalange. After the percutaneous pinning was performed, all subjects were requested to complete a questionnaire regarding the realism of the simulator and its expected usefulness in residency tactical training. This study was approved (expedited review) by the institutional review boards (RC-6301 and STUDY2016_00000519).
A tactile hand simulator, as shown in Figure 1, with a fifth metacarpal bone fracture was developed with input from clinical collaborators. The bicortical structure in the 3D printed skeleton is shown in Figure 2. The 3D printed mold designed to cast this simulator is shown in Figure 3. This hand simulator was given to participants as part of the questionnaire study. Figure 4 shows a trial session of a bone pin inserted across the fourth and fifth metacarpal bones. The skin was partially removed to reveal the pin through the metacarpal bones. Figure 5 shows pin tracks between the fourth and fifth metacarpal bones on a simulator used in this study (the bone pin was removed). Subjects' responses to the questionnaire are shown in Tables 1 through 3. See Supplemental Digital Content 1 (Table 1, http://links.lww.com/JG9/A22) for the complete responses.
All subjects have worked or are working with the residents, and the following are the consolidated results of the questionnaire:
- All agree that the tactile hand simulator is useful for residency training.
- All would recommend the simulator to their colleagues, and three of five indicated that they would go out of their way to do so.
- Three of five would use the current simulator in residency training.
- All of them are interested in testing the next iteration of the simulator because they see potential in the simulator as an effective training tool.
Subjects rated the realism of the material, purchase of pin in bone, and cortical–cancellous bone interface to be four of five on average. Other features were rated at least three of five on average. The lowest rated features are the skin and the joints. Subjects most commonly listed the anatomic accuracy and cortical–cancellous bone interface as the most important features and removable opaque skin covering as the least important.
Although some improvements to the simulator were suggested in the open-ended questions, two subjects expressed great enthusiasm for the simulator. One subject described the simulator as an excellent adjunct to residency training; another described the simulator training as a great way to build skills away from the OR and cadaver laboratory.
The learning of tactile skills, in addition to visual cues, on a tactile simulator enables low-risk tactical training sessions outside the OR. In this article, we present a tactile hand simulator, which is printed using a 3D printer. Its features include a bicortical structure in all bone pieces, a soft transparent tissue layer, and flexible joints. Responses from the questionnaire study indicate that it is an effective tool and an excellent adjunct to residency training. Although the sample size is small, all subjects are experienced surgeons who have trained or are training residents in the orthopaedics department. All of them indicated that the tactile hand simulator is realistic and would contribute positively to residency training even in its current form. In particular, they highly rated the tactile feedback of bone pinning in terms of pin purchase and cortical-cancellous interface.
This concept of the tactile simulator was first presented as a flexible clubfoot model that can support external fixation.10 Our hand simulator adds emphasis to the bicortical structure, which is an important training feature for percutaneous pinning. In this version of the simulator, the cancellous bone was created as a grid, which builds upward relative to the build plate. Thus, the cancellous structure is anisotropic and dependent on the print orientation, which may not be ideal if isotropy is required in a simulator. Additional studies are underway to create an isotropic cancellous structure. Since this study, we have reduced the cost of the simulator to below $100 by adapting the 3D printing procedure to a more economic desktop 3D printer while still preserving the bicortical structure. A removable skin layer was also included in this tactile hand simulator to stagger the learning curve for junior residents.
One of the major advantages of the 3D printed simulator is the ability to engineer custom conditions that cater to the mastery of the residents and reduce the stress of learning. Being just graduated from medical school and often not having used any surgical tools before, junior residents face a steep learning curve even while working on a cadaver. Our simulator provides the customization necessary to stagger the learning curve. For example, in training for percutaneous bone pinning, a junior resident may first practice without the opaque skin covering. This practice provides additional and immediate visual feedback to augment his or her psychomotor training.4 He or she can then add the opaque skin covering to increase the difficulty of the task. Although additional studies are necessary to conclude whether the visual cues had any notable effect on their mastery of percutaneous bone pinning, junior residents who trained in percutaneous bone pinning on our simulator performed better than did the control group in a blinded assessment in a separate ongoing study (data not yet published). We also observed greater slippage of the pin when the opaque skin was left on than when it was removed. This observation is in line with our expectation that the transparent gel provided visual cues to help them complete the task more efficiently. This mastery-based training makes learning more efficient and less daunting.13
Our simulator also facilitates the implementation of deliberate practice by providing a low-risk environment where residents can make mistakes and learn from them.4 This theory is supported by a recent study5 wherein medical students learned external cardiac anatomy better on 3D printed simulators than cadaver specimens because they were less apprehensive and anxious when working with the simulators. This strengthens our belief that 3D printed simulators may be able to fill the critical gaps between the literature, textbook images, cadaver training, and surgery.
Our simulator is also procedure based, incorporating only those features that are critical to the procedure to stagger the learning curve for new learners. This hand simulator was designed to not have details such as vasculatures that are not directly relevant to percutaneous pinning. Instead, it has features such as the bicortical structure that are specifically critical to the learning of percutaneous pinning. Besides reducing cost and waste, this approach to designing simulators also reduces distractions to the learning.
In conclusion, simulators focusing on tactile and visual feedback are perceived to be effective training tools to help residents achieve competency during residency training. However, Malik et al14 determined that funding and support are two of the main barriers to implementing the competency-based learning introduced by the Accreditation Council of Graduate Medical Education in 2001. Although 3D printing is a cost-effective method to create simulators, there may still need to be more support and funding for residency programs to adopt simulators that augment the Halsted model of residency training.
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Supplemental Digital Content
Copyright © 2018 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Orthopaedic Surgeons