Training on synthetic ethylene-vinyl acetate bench model allows novice medical students to acquire suture skills

PURPOSE: To assess the acquisition of suture skills by training on ethylene-vinyl acetate bench model in novice medical students. METHODS: Sixteen medical students without previous surgery experience (novices) were randomly divided into two groups. During one hour group A trained sutures on ethylene-vinyl acetate (EVA) bench model with feedback of instructors, while group B (control) received a faculty-directed training based on books and instructional videos. All students underwent a both pre-and post-tests to perform two-and three-dimensional sutures on ox tongue. All recorded performances were evaluated by two blinded evaluators, using the Global Rating Scale. RESULTS: Although both groups have had a better performance (p<0.05) in the post-test when compared with the pre-test, the analysis of post-test showed that group A (EVA) had a better performance (p<0.05) when compared with group B (control). CONCLUSION: The ethylene vinyl acetate bench model allowed the novice students to acquire suture skills faster when compared to the traditional model of teaching.


Introduction
Given that general practitioners are routinely faced with minor surgery interventions [1][2][3][4] and that most physicians do not get satisfactory basic surgical skills during their academic formation 5 , it is necessary to establish a training program aimed at the teaching and improving of these technical skills to students in training [1][2][3][4][5] .
In this context, as some practical activities with patients may infringe moral, ethical and legal aspects 6 , the training of technical skills outside the operating room based on simulation is becoming widely used in medical education [6][7][8] .
For this form of teaching and learning, many models and simulators have been described 7,8 .These models vary widely regarding their level of fidelity, as compared with the living human patient 7,8 .Although high-fidelity simulators are more attractive to trainees, there are some drawbacks that make them unsuitable for the teaching of basic skills 8 .Training on live or post-mortem animals and on fresh human cadavers (reality very close to the real) is currently discouraged because of infection risks, high costs, need for specialized facilities and legal and ethical aspects [6][7][8] .In addition, the difficult access to high-fidelity virtual reality simulators and their high costs 7,8 hinder their use, especially in developing countries 9,10 .
Alternatively, there are bench models 7,8 , that although considered as of low-fidelity, have advantages such as lower cost, portability, ability to be used in unsupervised practice and with the potential for repeated reuse of materials allowing students unlimited practice [6][7][8] .Recently, we proposed in this context the use of a synthetic ethylene-vinyl acetate (EVA) bench model to teach medical students the fundamental skills (suture techniques) required to assist with cutaneous surgical procedures and feel comfortable in the operating room 11 .In this previous report 11 , we include subjective observations about the acquisition of suture skills; however, in this scenario (simulated surgical training) the evaluation of performance and of this skills' gain should be objective 12 and preferably made by a previously validated test 13,14 .
Therefore, the purpose of this study was to evaluate the acquisition of suture skills with the training on EVA bench model in novice medical students, by means of a randomized, controlled and blinded study.A discussion with additional thoughts about how to use this synthetic model is also included.

Study participants
The protocol consisted of second-year medical students

Didactic teaching session and pre testing
Sixteen subjects were randomly selected from a group of 60 students who met the selection criteria outlined previously.
On the day of the experiment, all students were taught how to use surgical instruments, as well as the techniques for the types of sutures required, by means of a video presentation which was repeated and commenced upon six times (verbal teaching based on video).This stage took one hour.Next, all participants underwent an individual pre-test, which consisted of making five simple interrupted sutures (two-dimensional) and five half-buried mattress sutures (three-dimensional) for the closure of two incisions (8 x 2 cm each) on ox tongue.Each student was tested individually and had a total time of five minutes for each task.

Training phase
Immediately after the pre-test, all students were randomized into two groups of eight students each and began the tasks assigned to them.The two groups remained in separate rooms so they were unable to communicate with each other.
In Group A, students practiced with surgical instruments and suturing by using the EVA bench model (Figure 1) with help of instructors (simultaneous feedback) according to the training described by our group 11 .In group B (control), the students received a faculty-directed training based on visualization of learning materials (textbooks and video-lesson) on the handling of surgical instruments and the manufacture of sutures.In order to standardize the learning, the instructors were instructed to teach the skills using the same method.This stage lasted one hour for both groups.
Training on synthetic ethylene-vinyl acetate bench model allows novice medical students to acquire suture skills

Post testing
After the training, the instructors demonstrated to all students, for a period of the ten minutes, the making of simple interrupted sutures and half-buried mattress sutures.Immediately following this, the students were randomly assigned to a post-test (similar to pre-test).Each student was tested individually and had a total time of five minutes for each task.

Task evaluation
All pre-test and post-test maneuvers were recorded and saved.These digital videos were archived for later analysis and codified by using randomly assigned numbers by one of the investigators on the project.All of the recordings were independently evaluated in a blinded fashion by two surgical specialists who had no prior knowledge on the groups.The number of students who completed the proposed procedures (one or more stitches) and the number of stitches made were documented; the stitch was regarded as finalized only after the ends of the two surgical threads were cut.The Global Rating Scale (Table 1), previously validated 13,14 , was used to objectively evaluate the performance of each student in eight main areas.Each area was scored on a five-point scale; the lowest rating being one and the highest being five, making a maximum possible total score of 40 points.

Results
There was a difference in all evaluated parameters between the two groups, with Group A (trained on EVA model) showing better performance.The exception to this occurred in comparisons between groups that were performed in the pre-test.

Student numbers and sutures done
In the pre-test none of the 16 students managed to perform any of the two proposed procedures (no stitch) and therefore, there are no differences (p>0.05) between the two groups (Group A versus Group B).In the post-test, a larger number of students in group A carried out a larger number of stitches in both types of evaluated sutures when compared with group B (control), as shown in Table 2. Comparing the two evaluated periods (pre-test versus post-test), a larger number of students in both groups (A and B) carried out a larger number of stitches (both suture types) in the post-test period (p=0.0000 for all comparisons).

Global rating scale
In blinded evaluations of both pre-and post-tests, no inter-observer difference was detected between the examiners on the evaluation of means in Group A (EVA) for simple interrupted sutures or half-buried mattress sutures or in the analysis between means for group B (control) also for the two procedures (p>0.05 for all comparisons).
Objective assessments conducted in the pre-test were considered minimal (means equal to 8) in all 32 performances; and, therefore, there are no differences between the two groups (p>0.05).In the post-test, the average performances, evaluated using the Global Rating Scale in the performance of simple interrupted sutures, demonstrated that group A (22.13±6.52)compared to group B (13.19±5.48),presented a better performance (p=0.0001).
This difference also occurred in the manufacture of half-buried mattress sutures, in which group A (20.63±7.68)compared to group B (12.25±5.26),also showed a better performance (p=0.0006).Comparative analysis of mean examiner ratings based on the Global Rating Score is evidenced in the Figure 2.

Discussion
Although the technique of suturing is the foundation upon which most surgical skills will be built 15 (e.g., several cutaneous surgery procedures), such a foundation is not acquired by a large percentage of students during their training 5,15 .Many inanimate bench simulators have been described for their training 10,[16][17][18] .Since 2008 we 11 use the synthetic EVA bench model for the teaching of sutures during medical undergraduation.Recently, other authors 19 also described the same material (EVA) as an alternative to dermatology residents in the training of sutures.However, in these two reports 11,19 the acquisition of skills was based only on subjective perceptions; therefore, it does not express the actual level of acquired skills 20 , specifically with this bench model.
In our 11  or learned independently from a prepared text).The adoption of faculty-directed learning was based on the study 28 that showed that this form of teaching is superior to self-directed learning.The tools (videos and textbooks) of teaching used by the control group are recognized as a form of learning technical skills 29,30 .The number of instructors used (one instructor for every four students) was shown to be ideal for teaching suturing skills to medical students 15 .
We selected two types of sutures 31 , because the possibility of training two and three-dimensional sutures seems to be one of the advantages of using the EVA bench model 11,19 .
All parameters (knowledge, decision making, communication, and dexterity), which constitute the concept of "surgical competence" can be measured; however, the measurement of technical ability and dexterity is the most problematic one 32 .Some authors 33,34 carried out measurements of these technical skills after training on bench models; however, they did not use a previously validated test.The Global Rating Scale 13,14 adopted as an evaluation tool in this study is part of the Objective Structured Assessment of Technical Skills 14 , which is considered nowadays as the gold standard for the objective evaluation of teaching surgical skills 12 .
To the best of our knowledge, this is the first Brazilian study that evaluated objectively the teaching and learning of suturing skills in novice medical students, through training on lowfidelity bench model (EVA); there are similar Brazilian reports on the evaluation of other relevant issues in medical education 35,36 .
The results of this study show that a larger number of students who practiced on the EVA model were able to make a larger number of stitches with greater dexterity.This was also found in previous studies [23][24][25] , which demonstrated that training in low-fidelity bench models is significantly better than the training in the control group Students in the control group when confronted with the post-test, in most cases, failed to either begin making the stitches.
Only three students were able to perform simple interrupted sutures, with a total of 5 stitches (ranging from 0 to 2 stitches per student) and only one of them held two half-buried mattress sutures.Since these few students had better performances in the post-test (compared to the pre-test), we can infer that this form of teaching (faculty-directed learning from didactic materials) can also determine (to a lesser degree) a gain of skills; this corroborates the previously described subjective feeling that before the introduction of EVA, some students could perform minor procedures under supervision of the faculty mentor.
There were a number of limitations in this report that must be acknowledged.First, there was no comparison of the EVA model with another bench model.This occurred because an extensive literature review (Scielo, Medline, and Embase databases) revealed no relevant reports in English that showed the superiority of one high-fidelity model over a low-fidelity one, or the superiority of a low-fidelity model over another low-fidelity one, for the teaching of suture skills for medical students.In fact, there is, so far, no standardization on an ideal model for teaching and learning of suture techiniques 17 .In addition, studies [23][24][25] that compare different models (high fidelity versus low-fidelity) showed that there was a gain of surgical skills when both models were compared to training without simulation, but there are no differences between the models.In this context, the choice of a model to make comparisons with EVA model would be merely arbitrary and without scientific basis.
A second limitation was that the comparison used here (training on EVA versus faculty-directed learning based on educational materials) seems unnecessary at first, because it is described that there is more acquisition of technical skills when the training is based on simulation 37 .However, it is exactly this makes this comparison (training with simulator versus training without simulator) useful in the present study; if this comparative analysis were unfavorable to the use of EVA, the model might not be used/recommended as a tool of teaching, since it is known that simulated training is better 37 .Thus, by using a validated evaluation tool 13,14 , the claim that by the training on EVA model students acquire suture skills, becomes objective and specific to EVA; this claim was previously based only on subjective perceptions 11 and on studies that evaluated other low-fidelity simulators [23][24][25]  clarify doubts with the instructor (posterior feedback).In these moments, aspects such as spacing of stitches and eversion of the "wound edges" are evaluated and taught to the students again, having as a result a gain of skills over time.This form of teaching and learning (different teaching sessions spread over weeks with feedback from the instructor) has been described as the most effective method for teaching basic technical skills 28 .However, the time and the number of faculty surgeons available for this form of training is reduced 28 ; the use of non-surgeon skills coaches 39 , trained students (students as teachers) 40,41 or surgical residents 42 as instructors can alleviate these limitations of the method.
The goal of surgical simulator-based training is to help trainees acquire and refine the technical skills 8 , for a subsequent contact with the real world (transfer of skills) 6,23 .In previous literature, there is evidence that the technical skills developed in bench models can result in performance improvements in cadavers, animal models and in the operating room 6,[23][24][25] ; and that for beginning students in surgical practice, the transfer of skills to the clinical environment is as good when obtained from cheap low-fidelity models as when it derives from expensive highfidelity models or virtual reality simulators 7 .
Further studies are required to measure these aspects (transferability to clinical practice and retention of skills over time) using the EVA model.In addition, the acquisition of suture techniques with this model should be investigated for trainees in other levels of training (e.g., residents).
Training on EVA bench model enables novice students to acquire suture skills better than the faculty-directed learning from didactic materials.This model can be used as a tool for teaching and learning of two and three-dimensional sutures during medical undergraduation, mainly for beginning students in surgical practice.
with no surgical skills background (novices) from the School of Medical Sciences at the University of Marilia, Sao Paulo, Brazil.All students with prior exposure to any surgical skills (use of surgical instruments, in suturing techniques or other procedures) were excluded.All subjects signed an informed consent form approved by the Ethics Committee for Human and Animal Research at the University of Marilia.The present study and all the procedures related to it are in accordance with the Declaration of Helsinki 1975, as amended in 1983.

FIGURE 1 -
FIGURE 1 -Synthetic ethylene-vinyl acetate bench model simulating a (A-C) vertical mattress suture and a (D-F) subdermal interrupted suture.

FIGURE 2 -FIGURE 3 -
FIGURE 2 -Comparative analysis between all suture performances based on the Global Rating Scale of the both groups A (ethylene-vinyl acetate bench model) and B (control) for both types of stitches performed in the post-test.The heavy line is the median.The bars represent the range of the data.The symbols "*" indicate the outliers.
previous study, besides presenting the EVA model, we also observed subjectively that the students who were trained at the bench model were able of performing minor surgical procedures under supervision of faculty expert.However, before the introduction of EVA, some students without the simulatorbased training also presented similar results.Thus, it was unclear whether it was exactly the training on the EVA model that made this possible; or if, in fact, only the instructions during classes and during the surgical procedure were the main determinants of this performance.Although it seems obvious that the gain of skills through training in any model is superior compared to the non-training, in proposing a new model11 , this cannot be only in a subjectivity level20 , because in the teaching of surgical skills, the measurement of gains should be carried out by an objective evaluation method[12][13][14] .Thus, the main focus of this study was to determine whether training on the EVA model, considered as of low-fidelity, can be used/recommended as a tool for teaching sutures during the medical undergraduation, through a comparative analysis with the faculty-directed learning based on didactic materials (video and text about suture training).Therefore, the aim of the study is not ascertain if the EVA is superior or inferior to other types of bench models.In the present study, the option for the training during one hour and performing a pre-test after the students watched an instructional video were based on two reports 15,26 on the teaching of sutures for medical students.The use of a control group that received no additional training was based on previous studies 21-27 also on the acquisition of technical skills (training group versus notraining group, didactic training alone, no additional intervention,

TABLE 1 -
Global 13,14g Scale13,14used for the objective assessment of suture performances of students in the pre and posttests.Please rate the candidate's performance on the following scale:

TABLE 2 -
Comparative analysis of number of students that performed stitches and of number of stitches done by each group in the post-test.Group A = Ethylene-vinyl acetate bench model; Group B = Control; M = Mean; SD = Standard deviation; * Statistically significant.