Developing Neuraxial and Regional Pain Procedural Skills Through Innovative 3-Dimensional Printing Technology

Methods

Third- and fourth-year osteopathic medical students from A.T. Still University Kirksville College of Osteopathic Medicine and residents from Northeast Regional Medical Center were invited to participate in the study. Participation was voluntary. Residency types included internal medicine, anesthesia, osteopathic manipulative medicine, and family medicine. Participants used 3D-printed medical gel joint models made in-house for mastering joint injection techniques with ultrasonography guidance. The A.T. Still University-Kirksville institutional review board granted exempt status for all educational procedures used in the current study.

Three new models were developed and used in the current study (Figure 1). The cervical spine model included 7 cervical vertebrae with spinous and transverse processes, intervertebral discs, nerves, and vasculature. The lumbar puncture/spinal epidural model contained lumbar vertebrae L1-L5, intervertebral discs, ligamenta flava, epidural space, and subarachnoid space with cerebrospinal fluid. The pelvic model contained os coxae, lumbar vertebrae L4 and L5, intervertebral discs, nerves, sacrum, coccyx, ilium, sacroiliac joints, and posterior superior iliac spine.

Figure 1.

Cervical, lumbar, and pelvic 3D-printed models used in the joint injection technique laboratory.

Flexible intervertebral disks, nerves, and vasculature were printed using Cheetah flexible filaments (NinjaTek, Fenner Inc.) on an Afinia 3D printer. A Stratasys F123 Series: F170 printer was used to print the vertebrae, pelvis, and sacrum with acrylonitrile butadiene styrene filaments. After the models were printed and cleaned in an SCA-1200HT support removal system (Phoenix Analysis & Design Technologies), they were assembled using Gorilla glue gel and small screws. The printed nerves, vasculature, and rubber tubing (representing the spinal cord) were placed in their proper anatomical position. Some of the models were then coated with high-temperature silicone to minimize bubbles. The models were attached with screws to wooden stands to support them in the proper anatomical position.

Humimic Gel #0 (Humimic Medical Healthcare Products) is one of the most versatile gelatins used for medical imaging. The gel is clear and produces realistic tissue-like texture when imaged with ultrasonography. This gel was used to encase the models so blind insertion and ultrasonography-guided techniques could be used for injection procedures on all of the models. Molds were designed using aluminum sheet metal and flue pipe to ensure the proper shape and size for each model. The molds were attached to the wooden bases around the models with high-temperature fireplace sealant, flue tape, and steel duct clamps to ensure that the hot liquid gel did not leak. The gel was cut into small pieces and melted in 3-pound increments at 121°C. Once melted, it was poured into each mold and allowed to cool. Once the gel cooled and solidified, an electric heated knife and hot air gun were used to sculpt the molds into proper anatomical shapes.

The completed models were used in injection technique laboratories that taught needle-guidance procedures with the use of ultrasonography. Before participating in the laboratory, medical students and residents of the current study mastered basic ultrasonography techniques and applications through clinical ultrasonography coursework and monthly didactic ultrasonography sessions.²² The laboratory began with a presentation that explained the objectives and clinical relevance of the injection exercise. The presentation was followed by a live demonstration of the injection technique and ultrasonography scanning technique using the 3D-printed models (Figure 2). The models are also ideal for ultrasonography-guided techniques because the gel produces a realistic tissue-like texture when imaged. Participants used Mindray-5 ultrasonography machines with 10L4s linear ultrasonography transducer and a frequency bandwidth of 8.0/10.0/12.0 MHz (Shenzhen Mindray Bio-Medical Electronics Co.).

Figure 2.

Spine and pelvic models used in the joint injection technique laboratories. (A) 3D-printed medical gel cervical model with the needle showing facet joint access; (B) 3D-printed medical gel lumbar model with the needle showing lumbar/epidural access; (C) 3D-printed medical gel pelvic model with the needle showing sacroiliac joint access, where the inset shows the ultrasonography image indicating the needle position; (D) 3D-printed medical gel pelvic model with the needle showing caudal epidural access, where the inset shows the ultrasonography image indicating the needle position.

The objective of the injection ultrasonography laboratory was to identify anatomical structures of interest and perform injections. Students and residents had to identify the following anatomical structures to perform injections: C1-C7 spinous and transverse processes and facet joints on the cervical model; L1 through L5 spinous processes on the lumbar puncture model; and L4 and L5 spinous processes, sacroiliac joints, and caudal epidural region on the pelvic model.

After the training laboratory, participants were asked to complete a 17-item paper survey about their perceptions of the importance of the models for education and future practice. The survey was created specifically for the current study by the course director for the Clinical Ultrasonography course; it was voluntary, anonymous, and did not collect demographic information. The survey was validated using predoctoral fellows (completed 2 years of medical school, taking a year off to help faculty teach courses) to verify, items were readable, and interpreted consistently. Fifteen items were Likert-scale (strongly disagree, disagree, neither agree nor disagree, agree, and strongly agree) items. Those items evaluated participant comfort level with performing joint injections after using the models with ultrasonography needle guidance, overall satisfaction with the models, and likelihood of using 3D models in the future. Items also asked participants to compare commercial injection training models with the in-house 3D models (feel, anatomical correctness, and comfort when using the models). The last 2 survey items were open-ended items that asked, “What is one thing you would like to see as part of the Injection Lab regarding the use of simulation models that we did not include?,” and “Please leave comments about the use of 3D-printed models in medical education.”

The current study used a sample of convenience, so no formal sample size calculation was performed. Total scores for the 15 Likert-scale items (where strongly agree was defined as 5 and strongly disagree was defined as 1) were calculated for all participants. Survey responses were summarized with frequencies and percentages. Agree and strongly agree responses were combined and defined as suggesting agreement. Disagree and strongly disagree responses were also combined and defined as suggesting disagreement. A χ² test was used to compare the proportion of agreement between students and residents. The binomial test of proportion was used to compare the proportions of agreement and disagreement for all individual survey items. Data analysis was completed using SAS version 9.4 (SAS Institute, Inc.). P≤.05 was considered statistically significant.

Results

Fifteen medical students and 21 residents completed the survey. Combining all survey items for students and residents separately, 14 (94.7%) students and 18 (87.3%) residents agreed, no students and 1 (3.2%) resident disagreed, and 1 (5.3%) student and 2 (9.5%) residents were neutral on the importance of 3D-printed models for injection training (P=.004).

Responses for all participants on all survey items are summarized in the Table. For defined agreement responses, all participants thought that the 3D-printed models were easy to use, while a majority (34 [94.4%]) thought that they were a useful tool to provide injection training and that they increased participant comfort in performing joint injections (28 [77.8%]). Students and residents (35 [97.2%]) agreed the models were a reasonable alternative to commercial training models (22 [61.1%]) felt capable of successfully performing cervical and/or pelvic injections, and 23 (63.9%) felt capable of successfully performing a lumbar/epidural procedure. Most participants (34 [94.4%]) would have liked to use the 3D-printed models in the future for personal training purposes.

The majority believed that lumbar/epidural (34 [94.4%]), cervical facet joints (34 [94.4%]), sacroiliac (35 [97.2%]), and caudal epidural (34 [94.4%]) procedure training helped them better understand the injections with ultrasonography guidance and that the models would help them in their future practice and for development of their clinical skills (both 34 [94.4%]) (Table). They also believed that the 3D-printed models could improve the existing medical curriculum (35 [97.2%]).

Participant responses to the open-ended items indicated students felt more prepared for rotations and residents felt more confident about performing injection procedures later during their residency. Participants also indicated that visualizing anatomical structures inside the clear-gel models augmented their understanding of anatomy and the clinical relevance of the procedures. Overall, responses to the open-ended survey items seemed to suggest that participants were overwhelmingly positive about the incorporation of 3D-printed models in their education.

Discussion

In the current study, third- and fourth-year medical students and residents used in-house 3D-printed gel models for mastering joint injection techniques with ultrasonography guidance. Both students and residents agreed that 3D-printed models were helpful and easy to use, aided understanding of corresponding procedures, and increased comfort performing joint injections. Most believed that the new models were reasonable alternatives to commercial models, and more than half felt capable of successfully performing a lumbar epidural procedure and cervical or pelvic injections. All participants believed that 3D-printed models were a useful tool for injection training, and some indicated they would like to use the models in future for personal training purposes. The 3D-printed models developed for our study provided the same realistic feel for the various procedures as the commercial models, but had an additional benefit of allowing the trainees to visualize the key anatomical structures and their spatial relationships because of the transparent gel used as the model matrix. This visual and tactile feedback allowed trainees greater understanding of where they were in the body and what they were feeling.⁴⁷ Future models could have a skinlike layer to be more realistic and provide a more challenging and authentic injection experience.

Although simulation in medical training is well established⁴⁸ and efficient for emergency medicine, trauma, surgery, and critical care,^22,49,50 the upfront cost and associated maintenance of current commercial training models are limiting factors.⁵¹ Thus, students have reduced exposure to models during training, which places the burden of student education back onto the patient. More affordable training models would allow more access for students to learn and master various procedural skills, including needle handling.⁵² The use of 3D printing may be one way to reduce costs, as each model costs $400 to $500 USD to produce, which is a tenth of the cost of a commercial trainer.

With the increasing use of ultrasonography in medicine, ultrasonography-guided procedures are quickly becoming the standard of care.⁶ The 3D-printed models developed for the current study were specifically made with materials that were compatible with ultrasonography and allowed for the visualization of all anatomic structures. Thus, students and residents had the opportunity to master procedures with or without image guidance. Mastery of injection skills is critical for patient safety and physician proficiency in order to avoid medical errors in future practice.

Previous research findings have highlighted the importance of simulation-based medical education: students trained to use ultrasonography with virtual trainers were better prepared to interpret images than classroom-based learners.⁵³ Results of the current study are consistent with these data. The 3D models allowed medical students and residents to visually identify skeletal structures on the models and on ultrasonography images since the surrounding medical gel was clear. This visual identification of skeletal structures augmented with ultrasonography increased participants’ confidence with the injection techniques and ultrasonography image interpretation. All participants were able to obtain images of the lumbar spine, facet joints, sacroiliac joints, and caudal epidural area, and the majority believed that the training models helped them better understand ultrasonography guidance for injections.

The most challenging procedures in the current study were lumbar epidural and cervical injections; 61% of participants felt capable of successfully performing cervical and/or pelvic injections, and 64% felt capable of successfully performing a lumbar/epidural procedure. These results correlate well with published data that indicated lumbar epidural injections presented major procedural challenges to practitioners with limited experience.^54-58

The ability to correctly perform injection procedures is an important aspect of medical training because it affects physician competence and patient safety. In one study,⁵⁹ physicians trained with simulation-based techniques outperformed and were more competent than traditionally trained physicians for a specific procedure. The use of simulation-based education also improved patient safety.⁵⁹ Given these benefits, it is important to begin simulation training at the undergraduate medical student level and continue this training during residency.

Results of the current study showed that most participants believed that the new 3D-printed models could improve the existing medical curriculum and were beneficial for the development of clinical skills, which is consistent with current reviews of the role of simulation in medical education.⁵⁹ Both students and residents believed that training with 3D-models aided their future practice, which indicates that participants were receptive to incorporating the models as a new technology into their education. Participants reported that being able to visualize anatomical structures inside the clear-gel models augmented their understanding of anatomy and the clinical relevance of the procedures. Future studies should consider using dyes with the needle-guided techniques, so trainees could also see how medications spread after injection.

This study was limited by its small size. Sample size was restricted by the number of third- and fourth-year medical students and residents at the study site. Future studies should include a large sample size or a use multi-institutional approach. Other limitations are that we did not use a control group or perform quality assurance on the manufactured models. Our survey was created specifically for the current study and was not validated.

Conclusion

Our results suggested that 3D-printed models provided realistic training for injection procedures and may serve as a cost-saving alternative to commercial training models. This training could begin at the undergraduate medical student level and progress through residency. The 3D-printed spine and pelvic models were well received by both medical students and residents. Furthermore, the models seemed to allow the trainees to quickly master injection techniques, which would potentially improve their future patient care.