The use of 3D printing for osteopathic medical education of rib disorders

Methods

The Nova Southeastern University Institutional Review Board determined that this study exempt under 45 CFR 46.101(b). The project adhered to policies outlined in the Family Educational Rights and Privacy Act (FERPA) (20 U.S.C. § 1232g; 34 CFR Part 99) regarding the protection of students’ educational records and privacy.

The prototype rib model was developed between October 2018 and February 2019. Once the prototype design was finalized, the printing of individual parts and assembly of complete models were completed in February and March 2019. The study took place on March 21st, 2019, over two separate lab sessions that lasted approximately 2 hours each. Data analysis initially began in April 2019 and was completed in August 2020.

Participants were first-year osteopathic medical students enrolled at a large osteopathic medical school in Florida. Two hundred and thirty-seven of 257 students enrolled in the class participated in the study. All students who participated in the study received a letter explaining the research and requesting informed consent. As this was a single-blind qualitative study, participants were assigned at random to a comparison group or control group designation within the osteopathic laboratory class. The participants were placed on a deidentified Excel spreadsheet (Microsoft, Inc.) and assigned a comparison group or control group designation with the RAND (random) function on excel. Students from the comparison group participated in the first laboratory session and received instruction with the novel 3D rib model; students from the control group participated in the second laboratory session and received instruction with the traditional model.

3D printed rib model and traditional rib model

The prototype 3D rib model was designed to emulate rib biomechanics in relation to the vertebra and various rib somatic dysfunctions (Figure 1). Each model was designed with three thoracic vertebra levels with a respective rib on each side, for a total of six ribs. The prototype model was built from Acrylonitrile Butadiene Styrene (ABS) plastic material [15] (Figure 2). The individual materials utilized in assembly included individual printed ribs and vertebrae, screws, plastic rings, and foam sheets to serve as intervertebral disks. The ball-joint for articulation was adapted from Gerefalk’s “Locking Ball and Socket Arm” and licensed under Creative Commons CC BY-SA 3.0 for adaptation [16]. The rib and vertebra were adapted by Mitsuhashi’s “BodyParts3D,” and licensed under CC Attribution-Share Alike 2.1 Japan [17]. Files were exported out of .obj format and reformatted for Meshmixer software (Autodesk, Inc). Within the Meshmixer program, the joint was placed at the superior costal facets on both sides of the vertebra. The ball portion was placed on the articular rib tubercle to allow for attachment to the receptive joint on the vertebra to form the articulation of the completed rib model. The ball and socket were locked with an equally 3D printed plastic ring that wrapped around the joint. A screw was used to lock this plastic ring in place and tighten around the joint for continued stabilization. The prints were scaled up by 10% and printed at default balanced settings with 10% infill & supports. Because of the novel joint design, both pump handle and bucket handle rib motions could be accurately displayed. In relation to the joint, the rib could move within a 90-degree arch in the transverse plane and a 180° arch in the sagittal plane. This allowed the model to display the elevation and forward motion of the ribs in pump handle motion. The model also had the ability to raise and lower the middle of the rib, representing bucket handle movement (Figure 3).

Figure 1:

Posterolateral view of the assembled three-dimensional prototype rib model.

Figure 2:

Superior and anterior view of an assembled three-dimensional prototype rib model and the individual materials used in assembly: individual ribs and vertebrae, screws, plastic rings, and foam sheets cut in the shape of the vertebral body of the vertebrae.

Figure 3:

Anterior view of the traditional model.

The traditional model (Figure 4) was not designed to emulate physiological rib movement or rib somatic dysfunction. The traditional rib model did not have the novel ball and socket, nor the locking plastic ring design. The traditional rib model was also not produced with Meshmixer software nor through 3D printing. This model had the same dimensions of vertebrae and ribs of the 3D prototype rib model, and it also included a sternum and manubrium like that of a traditional plastic skeletal model. The traditional model also included thoracic ribs 1–12 but lacked rib biomechanics.

Figure 4:

Lateral view of the traditional model.

Paper surveys were delivered to each individual student and collected by three authors (K.M., A.R., M.L.). On study enrollment, participants completed an entry survey consisting of three questions about their knowledge of OMTs regarding rib diagnosis and treatment (Figure 5). Each question had a single correct answer out of four possible answers. Each item was scored separately as incorrect or correct (dichotomous variable). Possible total scores ranged from 3–9, with higher scores indicating more questions answered correctly.

Figure 5:

Entry and exit survey questions regarding rib knowledge.

OMM, osteopathic manipulative medicine; OMT, osteopathic manipulative treatment.

After completion of the entry survey, each group participated in a standardized OMT lecture during a laboratory session where they were taught how to diagnose and treat rib dysfunctions with their group’s respective rib model. The lecture consisted of three, 10- to 15-minute sessions by the main instructor situated in the center of the room; mounted computer monitors throughout the classroom displayed the instructor, enabling all students to have highly visible instruction. The main instructor was the Chairman of the Department of Osteopathic Principles and Practices, who was not an author on this paper. During the first session, the instructor demonstrated and explained the various movements of the ribs using the selected model; during the second session, the instructor demonstrated inhaled somatic dysfunctions; during the third session, the instructor demonstrated exhaled somatic dysfunctions. The instructor also demonstrated how to treat a given dysfunction with the muscle energy technique on a student volunteer during the second and third sessions.

Each session was followed by an additional 10–15-minute session with smaller groups of five to seven students. These were supervised by a physician, physical therapist, or predoctoral osteopathic practices and principles fellow. During the smaller group sessions, each student was able to use their respective model to visualize the pump-handle and bucket-handle motions. Also, students were able to visualize inhaled and exhaled somatic dysfunctions. The amount of time spent for the lesson, educational content, and main class instructor were standardized (constant) across each group (Figure 6). At the end of the laboratory session, participants completed an exit survey that evaluated knowledge learned, select demographics (age, sex, and the highest level of completed education before entering medical school), and subjective evaluations of rib models.

Figure 6:

Exit survey questions assessing participant demographics and evaluation of the 3D model. OMT, osteopathic manipulative therapy; OPP, osteopathic principles and practice.

The exit survey (Figure 6) included the same three items in the entry survey, along with seven additional items assessing student perceptions of the models. Six of these additional items used a visual analog scale (0–10) for responses, with another using a dichotomous response set (yes/no) to assess whether the participant felt the use of models enhanced their understanding of rib anatomy, dysfunction, and treatment (Figure 7). The final item assessed the participants’ perceived minimum amount of necessary exposure time to the new rib model to facilitate learning rib somatic dysfunctions.

Figure 7:

Exit survey question assessing perceived learning time.

Results

Two-hundred and fifty-seven students were eligible for the study and 237 participated (92%).

Thirteen participants (5.5%) were age 21 years or younger, 185 (78.1%) participants were age 22–26, 35 (14.8%) were age 27–31, three (1.3%) were age 32–36, and one (0.4%) was age 36–40. One hundred and eleven (46.8%) participants were men and 126 (53.2%) participants were women. One hundred and seventy-nine (75.5%) participants held a Bachelor’s degree, 57 (24.1%) held both a Bachelor’s and Master’s, and one (0.4%) held other degrees. We did not identify any statistical relationships between the characteristic demographics of the sample group and the results of the study.

In both groups, 235 (99.2%) students agreed that the use of models enhances their understanding of rib anatomy, dysfunction, and treatment. Results also showed that students in both groups were interested in learning how to diagnose and treat rib somatic dysfunctions with OMT (mean value on analog 11-point scale, 7.52; standard deviation [SD], 2.403). Students in both groups felt their model accurately depicted the material presented (mean value on analog 11-point scale, 9.3; SD, 1.196). Students in both groups felt rib models were helpful in their education (mean value on analog 11-point scale, 9.08; SD, 1.397).

The independent t-test results showed that the comparison group (n=114) had higher scores (mean, 9.55 [SD, 0.978]) when queried whether they felt the model accurately depicted the material presented when compared with the control group (mean, 9.06 [SD, 1.33]; t(235) = 3.253; p=0.01).

The chi-square test of goodness-of-fit showed that the differences between the correct answers chosen by participants in the two groups for Item 3 (a case-based question asking students which rib they would treat for a patient presenting to an OMT clinic) was statistically significant, even though both groups scored similarly on this item during the entry survey (χ² [1, n=237]=5.97; p=0.015; 51.9% correct in comparison group vs. 48.1% in control group).

Table 1 shows summary statistics for the entry and exit survey items.

A post-hoc analysis was conducted to assess the power to detect a medium effect size between the experimental group (n=114) and the control group (n=123) in resulting knowledge scores. Our study (n=237, 0.05 alpha, 2-tailed test), had power in excess of 0.969 given a population correlation of medium effect size (d=0.50), power of 0.86 given a population correlation of 0.40, power of 0.63 given a population correlation of 0.30, power of 0.33 given a population correlation of 0.20, and power of 0.12 given a population correlation of 0.10. For the chi-square goodness of fit test, a post-hoc analysis was conducted to assess the power to determine if there were any significant differences in the responses between the experimental and control groups’ entry and exit surveys. For this test, our study had power in excess of 0.964 given a population correlation of medium effect size (d=0.30). Thus, our study was well-suited for detecting relatively large population effects — although perhaps not well-designed for finding (or establishing the existence of) smaller effects [18].

Discussion

On survey analysis, a very high percentage of students agreed that using any model enhanced their understanding of rib anatomy, dysfunction, and treatment. Further, students in this study generally agreed that the use of models, whether 3D printed or not, could affect education on rib anatomy, somatic dysfunction, and treatment. This is possibly due to the ability of models to help visualize the motion and position of each rib in relation to a particular rib somatic dysfunction diagnosis. Statistical analysis revealed that a significant number of students did see some benefit from the use of models. This conclusion aligns with the use of other 3D printed models in the literature, such as a study that compared the effectiveness of 3D printed models vs. cadaveric material and found significantly higher post-test scores in the 3D prints group compared to the cadaveric materials [8]. Thus, the 3D printed model prototyped for this experiment was designed to emulate rib dysfunctions that would otherwise be difficult to visualize. A limitation of the prototyped design was that the model was unable to emulate caliper rib motion seen in ribs 11 and 12. While the three vertebra and respective ribs were able to emulate pump and bucket handle motions seen in ribs 1–10, the caliper rib motions would require a smaller set of ribs and a different design in order to emulate that unique motion. A future design would create a completed thoracic vertebra that would include ribs 1–12 to emulate all three types of rib motions.

An independent samples t-test of the study revealed that the comparison group had higher scores in feeling the model accurately depicted the material presented than those in the control group. This finding suggests that the 3D printed prototype was successful in emulating somatic rib dysfunction in comparison with a traditional static rib model.

The chi-square of goodness-of-fit also revealed that a statistically significant number of students in the comparison group chose the correct answer on the exit survey about a question requiring spatial understanding more than students in the control group. Both groups scored similarly on this item during the entry survey. This finding shows that the 3D model may improve a student’s understanding through the enhancement of spatial understanding. It is important to note that more research is needed to determine the viability of 3D printing in clinical education. Direct causation could not be determined in this study, as there are other variables to consider in this finding. It is possible that using models in general, regardless of the model type, could contribute to this increase in understanding. Also, both groups were instructed on the diagnosis and treatment of somatic rib dysfunction after the entry survey, which may also correlate to the improvement of understanding. This study is preliminary and serves as an introduction to the use of 3D printing in osteopathic medicine. Additional research should focus on other osteopathic concepts such as sacral and vertebral dysfunction, in addition to rib dysfunction, to fully evaluate the use of 3D models in osteopathic medicine.

While this study was very limited in its ability to support the enhancement of osteopathic education, the study does serve as a proof of concept. 3D printing offers an inexpensive production of any prototype design. ABS is a hard plastic that can create a product that is both durable and inexpensive [19]. Materials like ABS are typically utilized to produce sporting equipment, protective headgear, and bumpers for the automotive industry [19]. A review of cost revealed that 145.3g of the plastic filament were required to complete a single rib model. Each gram of ABS costs 0.022 cents, resulting in each model costing only $3.20 to produce. Additional models produced via 3D printing will likely cost a similar amount. This contrasts with other forms of manufacturing, where full rib models can cost up to $402 [20]. As such, 3D printing offers a cost-effective solution in designing models for osteopathic medicine. Osteopathic physicians should be aware of these findings due to the ability for 3D printing to serve as an alternative method of producing highly specific models to demonstrate osteopathic concepts. Further research could strengthen data on the use of such 3D printed models targeting different OMTs. Examples of future trials of 3D printed models could include prototype sacrum and pelvis models; these could likewise be tested with surveys and statistical analysis.

Conclusions

The results of the study suggest that 3D printed models may serve as useful and effective educational adjuncts to demonstrate somatic dysfunctions of the rib cage during teaching of osteopathic principles because they enable spatial visualization, thus potentially improving student understanding and satisfaction in the diagnosis and treatment of rib somatic dysfunction.

In addition to showing increased perceived student satisfaction through the use of these models, our results showed that students educated with our 3D prototype model also more often correctly answered questions about rib mechanics than their counterparts educated with a traditional model, suggesting that the use of 3D models aided in student understanding. Considering at the minimal cost of only $3.20 to produce each model, 3D printing may offer a more financially appealing alternative compared with other traditional static anatomic models. Future research should focus on designing additional models on other osteopathic concepts to enforce this novel adjunct to teaching.