The reporting of this pre-post simulation study was performed in according to the STROBE guidelines (STROBE: Strengthening the Reporting of Observational Studies in Epidemiology) [7].

Setting

This pre- post simulation study was conducted at an academic level one trauma center in March 2024. The operative rooms of the surgical research facilities of the hospital were used. The room was equipped with a C-Arm and a radiolucent operation table, which were utilized for the study. Participation in the model was enabled for one entire day. Since this study presented a surgical simulation on synthetic bones and medical personnel took part voluntarily on their own time it is considered pursuant to Art. 2 (outside scope) of the Swiss Federal Act on Research involving Human Beings (Human Research Act, HRA). All participants provided informed consent.

Participants

The invitation to participate in this simulation was distributed to the trauma surgery team of the hospital (residents and consultants). Participation was not mandatory and was only realized on the surgeons’ individual behalf and in consideration of individual obligations in the clinical routine. Participants were stratified to a random number to account for anonymization during further analysis.

Questionnaire

Participants were asked to fill out a questionnaire, half of which were required to answer before and the other half after completing the simulation. Answers were either provided on a 10-point Likert scale (10-LS), a binary option (yes/no) or free to fill to the respective nature of the question to account for suitable analysis. On the 10-point Likert scale [1], indicated the lowest agreement/negative, and [10] indicated the highest agreement/positive.

Questions before the simulation (part A)

Are you still in residency? (yes/no)

How many years of experience do you have? (Free to fill, numeric)

Did you have experience with any other SI simulator in the past (yes/no)?

Do you think that training with an SI simulator can improve your ability to place SI screws? (10-LS)

How prepared do you feel to place SI-screws in an emergency situation? (10-LS)

How confident are you with intraoperative pelvic imaging (inlet/outlet)? (10-LS)

How confident do you feel with the installation of an external fixator for the pelvis? (10-LS)

Questions after the simulation (part B)

The SI-Simulator is a realistic model for placing SI-Screws. (10-LS)

In the future, I would like to use this SI-Simulator to improve my skills further. (10-LS)

Training with this SI simulator can improve my ability to place SI screws. (10-LS)

How prepared do you feel to place SI-screws in an emergency situation now? (10-LS)

How confident do you feel with intraoperative pelvic imaging (inlet/outlet view)? (10-LS)

How confident do you feel with the installation of an external fixator of the pelvis after the simulator? (10-LS)

Further comments (free to fill).

Secondary outcome variables

In addition to the subjective questionnaire, objective outcome parameters were assessed by the organization team of the simulator. These included the amount of radiation in mGray (automatically measured by the C-Arm for each participant), the time of total intervention and the two separate surgical steps (external fixation and SI-Screw). Further parameters assessed were damage of the balloon placed in the pelvic cavity, which simulated damage to the anatomic structures, and overall anatomic reduction, which was rated by the chief pelvic surgeon (range: bad-moderate-good). Sacroiliac screws were assessed for cortical (nonforaminal) and foraminal breaches, and the number of redirections/repositionings of the guidewire or screw was counted. The external fixator was assessed for malpositioning (i.e., contact with the intrapelvic cavity or acetabular joint). These parameters were assessed radiologically as well as by visual inspection of the synthetic pelvis after removal of the soft-tissue-mat.

Conduction of the pelvic fracture model

Our model was adapted from the pelvic simulator described by Tucker N and Mauffrey C et al., as seen and described on “The Ortho academy” website, a free, online platform developed with the purpose to disseminate global education in pelvic and acetabular surgery (https://www.theorthoacademy.com/) [3, 8].

SYNBONE® pelvis models with radiopaque coating were utilized for this study (Model 4060.9, SYNBONE®, Zizers Switzerland). Modifications for fracture simulation were incorporated as described subsequently:

First, we drilled in three places at the top and bottom of both ends of the mounting block and fixed it to the wooden plate with three metal screws. The polyethylene part of the mounting block was shaved manually to fit the back posterior part of the sacral bone and allow plastic-screw application through the S2 foramina into the mounting block.

A surgical wire was applied to the automated driller to then drill through the symphysis in an X-shape from anterior and posterior directions. Afterwards, the symphysis was cut with a scalpel, and two cable ties were applied through the predrilled holes and strapped loosely to ensure instability.

The same procedure was used for the posterior part of the pelvic ring. Two parallel holes were screwed from the back of the right ilium toward the top of the sacrum outside of the direct sacroiliac joint. Next, one cable tie was inserted back and forth through the two holes and closed loosely.

Afterwards, the sacroiliac joint was cut with a scalpel, resulting in complete instability of the right hemipelvis, which was only held loosely by the cable wires.

A balloon with a diameter of 12 cm was placed inside the pelvis to simulate intrapelvic organs. Finally, the pelvic model structure was wrapped with a 0.5 cm thick, white polyester/polyurethan mat to simulate soft tissue coverage (Vlieseline Style-Vil). The edges of the mat and the back of the wooden plate were secured with staples. A collection of images from the simulation is presented in Fig. 1. The entire list of materials utilized is provided as an additional file (see Additional file 1).

Fig. 1

Pelvic model and postoperative assessment. (A) Symphyseal disruption and fixation, (B) Sacroiliac disruption and fixation, (C) Pelvic model mounted on a wooden plate, (D) Sacroiliac screw application under fluoroscopy, (E) Intrapelvic balloon with penetrating external fixator, (F) Sacral bone with assessment of foraminal penetration on S1 level

Conduction of the simulation

According to the institutions radioprotective guidelines, participants were equipped with X-ray protective clothing and were not allowed to observe other participants during the simulation to control for a passive learning effect. Three conductors of the simulator (FK, KS, RP) attended the simulation and acted as operational personal. One conductor was in charge of positioning the C-Arm and performing the intraoperative imaging according to the participants’ request. The other ones handed over the requested surgical material and documented the a priori defined objective outcome parameters (i.e., time). Standard surgical material for these procedures was provided nonsterile.

Before the simulation started, the participant was required to answer questionnaire part A.

At the beginning of each round, the pelvis was already covered in the soft-tissue-mat and placed on the operation table at a 30° anterior tilt to account for anatomical positioning. Before the start, the participant was instructed on a suspected unstable pelvic ring in the synthetic pelvic model and asked to perform (1) external fixation of the pelvis either using a subcristal or supra-acetabular approach, (2) sacroiliac screw placement on the injured side and (3) reduction of the anterior and posterior pelvic ring. The participants was required to defect the injured side on their own and perform the aforementioned procedures. Intraoperative imaging was performed according to the participants’ instructions by In-, Outlet, Lateral and anterior imaging to simulate clinical practice at best. The participants could choose between cannulated, fully threated and partially threaded sacroiliac screws. The external fixator consisted of two Schanz pins with associated rods and clamps.

Fig. 2

Intraoperative Imaging of Rescue Screw application. (A) Fluoroscopic presentation of the simulator with symphyseal and sacroiliac disruption on the right side, (B/C), Guidewire instrumentation on S1 level, (D) SI-screw application, (E) Postoperative imaging assessment with insufficient reduction of the posterior ring

When the participant considered both operative steps to be completed, the soft-tissue mat was removed, and the reduction and placement of the screws and external fixator were inspected. Intraoperative images are presented in Fig. 2. Following the exercise, the participant were asked to complete the second part of the survey (part B).

Data analysis

Continuous data are presented as the mean and standard deviation, and categorical variables are presented as numbers and percentages. Missing data was planned to be excluded from the analysis, yet all data points could be collected. Statistical analysis was performed in R using the ‘Stat’ and ‘Tableone’ packages and the “ggplot2” package for the creation of figures [9]. MS-Excel was used for data visualization. The data were visually checked for normality using histograms. Categorical binary outcome data were assessed using a one-tailed Fisher’s exact test, and demographic data were assessed using a two-tailed Fisher’s exact test. Dependent parameters were assessed using a paired Wilcoxon test. Continuous parameters were analyzed using Student’s t test. The significance level was set at 0.05.

Validity assessment

Messick´s framework for construct validity was applied retrospectively to evaluate the effectiveness of our simulation model [10]. All five components of Messick´s framework were assessed: content, substantive, structural, generalizability and consequential validity.