The Impact of Simulator Size on Forces Generated in the Performance of a Defined Intracorporeal Suturing Task: A Pilot Study

Abstract

Background:

In pediatric minimal access surgery, the operative domain may vary from that of an adult to that of a neonate. This study aimed to quantify the impact of decreased operative domain on forces generated in the performance of a defined intracorporeal suturing task.

Methods:

One hundred five participants performed a defined intracorporeal suturing task in small and large simulators. Time to task completion and force analysis parameters (FAPs = total, maximum, and mean forces in X, Y, and Z axes) were measured. Expertise level was assigned based on the number of laparoscopic cases. Outcomes were analyzed using paired sample t-tests, P value of <.05.

Results:

Time to task completion varied significantly for experts between adult and pediatric simulators but not for intermediates or novices. Total, maximum, and mean forces in the X (“side to side”) axis were significantly greater in the larger laparoscopic simulator for all levels of expertise. In the Y axis (“in and out” movement) and Z axis (“up and down” movement), total and mean forces were higher in the adult simulator regardless of the level of expertise. Differences in maximum force between the adult and pediatric simulators in the Z axis (“up and down” movement) varied significantly for novices and intermediates but not for experts.

Conclusion:

Forces were greater, particularly in the side-to-side plane, in the larger simulator for participants of all levels in the performance of this defined intracorporeal suturing task. Further analysis will determine the reasons for and implications of the increased force parameters in the simulator of larger domain.

Introduction

Laparoscopic surgical interventions, while offering advantages such as reduced recovery times and improved patient satisfaction, are hampered by technical challenges such as loss of haptic feedback and decreased scope of manual dexterity.^1–5 As a result of these challenges, the learning curve for acquisition of technical skills is steep. With specific regard to forces generated in laparoscopic surgery, it is recognized that their excessive or inappropriate use is a significant cause of operative errors.⁶ The development of appropriate skills for the handling of tissue and moderation in the use of force are therefore relevant but challenging aspects of surgical education.^7–9 While loss of haptic feedback is recognized as a major factor contributing to the challenge in teaching the appropriate use of force in laparoscopic surgery,^4,9 there are no studies looking at the impact of operative domain on the forces generated.

Simulation-based training allows trainees to practice laparoscopic skills in an ex vivo setting and allows their skills to be evaluated before patient interventions.^10,11 Structured curricula using laparoscopic simulation-based training have been shown to shorten the learning curve of trainee surgeons and improve their performance in the operating room.^12–16 Traditional measures of performance include time to task completion and precision.¹⁷ More recent innovations have allowed the measurement of motion analysis parameters (e.g., path lengths, extreme motion events).^18–20 The measurement of force also offers the potential for assessment of skill, and may be valuable in the discrimination of safe tissue handling and secure knot-tying. The latter may have implications regarding clinical outcomes.^9,21,22 Measurement of force is being integrated into laparoscopic simulation, and preliminary validation has been established.^23–25

Pediatric minimal access surgery (MAS) has a unique set of challenges, the most obvious of which is the variability in operative domain.^26,27 While the implications of diminishing domain have been documented in terms of motion analysis, no data exist regarding the impact of a smaller working space on force.^28,29 This pilot study was undertaken to quantify the impact of decreased operative domain within a simulator on the forces generated in the performance of a defined intracorporeal suturing task. In so doing, the goal was to better understand the use of force in simulators of varying sizes, and gain insight into implications on education and assessment.

Materials and Methods

Simulators

Two simulators were constructed as outlined previously with a low-cost box design.²⁷ The larger box internal dimensions were akin to that of the adult fundamentals of laparoscopic surgery simulator (50 cm [length] × 37 cm [width] × 18.5 cm [height]). The smaller box internal dimensions were 18 cm (length) × 10 cm (width) × 9 cm (height).²⁷ Both simulators were easily assembled and disassembled for ease of transport and use. Both used a webcam, so any computer could be used as the screen. Costs of both simulators were kept as low as possible to allow global access and averaged 350 USD per simulator.

Candidates and testing

One hundred five participants were recruited at an education booth of the 2016 International Pediatric Endosurgical Group (IPEG) conference. Informed consent was sought from each candidate per a protocol approved by the Hospital for Sick Children (REB# 1000025362). The participants were asked to perform the same intracorporeal suturing task in the adult and the pediatric simulator. Candidates were stratified according to the level of expertise: novice (<10 pediatric or adult laparoscopic procedures/year), intermediate (10–50 pediatric laparoscopic procedures/year), and expert (>50 pediatric laparoscopic procedures/year).

Defined intracorporeal suturing task

Three-millimeter instruments were used in the smaller simulator and 5-mm instruments were used in the larger simulator. The suture used was 2-0 silk on an SH needle for the larger simulator, and 4-0 silk on an RB-1 needle for the smaller simulator. The silk was cut to a 9–10 cm length. The suture was placed at a predetermined position within the larger or smaller simulator. The candidate was expected to grasp and correctly position the suture on a laparoscopic needle driver. The suture was passed through clearly drawn target points on either side of a slit in a Penrose drain. The size of the Penrose drain was a half-inch diameter for the larger simulator and a quarter-inch diameter for the smaller simulator, cut to a 25-mm length for the larger simulator and 15-mm length for the smaller simulator, and secured with a corresponding size piece of Velcro to an underlying board. After passing the needle of the suture from one side of the Penrose drain to the other, the participant tied one surgeon's knot (double throw) followed by two simple knots (single throw).

Data collection and analysis

To measure force, we used a 3D mouse (DX-700034 Spacenavigator for Notebooks), which is manufactured by 3Dconnexion (MA). This provided data on translational and rotational forces in X, Y, and Z axes. The mouse was held in place by a second 3D-printed housing unit, which was fastened to an optical bread board. The 3D mouse was connected to a personal computer and interfaced in Java by using a Java input library. The 3D mouse is polled at a rate of 40 Hz, providing us with force in all three directions along with the torque about each axis. The output of the mouse was calibrated to convert its movement into force measurements. This was achieved by applying a known force in each direction and mapping the output of the mouse to the applied force. Raw force data of each participant were exported as text files for postprocessing. The data were then processed using Matlab and converted into N (Newtons). Mean force, maximum force, and the total force exerted over the extent of the task were determined.

Statistical analysis

Results are reported as mean ± SD for normal distribution. Statistical analysis was performed using SPSS version 25 (Statistical Processing for Social Sciences, IBM Corporation, Armonk, NY). Paired two-tailed Student's t-test analysis was undertaken for comparison of the total, maximum, and mean force in each axis between the larger and smaller simulators for experts, intermediates, and novices. Statistical significance was determined at P < .05.

Results

Participant demographics

One hundred five participants were recruited to undertake the tasks, the majority of whom were attending surgeons (n = 82, 78%) (Table 1). Ninety-nine participants completed the task in both simulators. Demographics of expertise level are outlined in Table 1. There were 20 novices (19%), 54 intermediates (51%), and 31 experts (30%) as defined by case number (Table 1).

Table 1.

Expertise Levels of Participants

	Total participants n = 105
Professional level
Resident	13
Fellow	10
Attending	82
Case numbers
Novice (<10/year)	20
Intermediate (10–50/year)	54
Expert (>50/year)	31
Completed both tasks
Novice (<10/year)	17
Intermediate (10–50/year)	52
Expert (>50/year)	30

One hundred five participants at the 2016 IPEG meeting were assigned to expertise levels based on the number of cases completed in the past year. Ninety-nine participants completed both tasks.

Force analysis

Ninety-nine participants completed the intracorporeal suturing task in both simulators, and successfully recorded results for time to task completion and measurement of forces generated (Table 2). Total forces generated to complete the task were higher in the larger laparoscopic simulator for novice, intermediate, and expert participants in all axes (Table 2). Mean forces were also higher in the larger laparoscopic simulator for all expertise groups in all axes (Table 2). Max forces were higher in the larger laparoscopic simulator in the X axis (“side-to-side”). Max forces were not different between the simulators in the Y axis (“in and out”). Max forces in the Z axis (“up and down”) were significantly higher in the larger simulator for intermediates and novices but not for experts.

Table 2.

Force Analysis

	Expert (>50 cases)	Intermediate (10–50 cases)	Novice (<10 cases)
	n = 17	n = 52	n = 30
X axis (mean N ± SD) (“side-to-side” movement)
Adult simulator: total force	9353 ± 8236	7776 ± 7560	9565 ± 7644
Pediatric simulator: total force	3427 ± 2915	3183 ± 1842	3892 ± 2178
	P = .008	P = .001	P = .001
Adult simulator: max force	2.8 ± 0.8	2.8 ± 0.7	2.9 ± 0.7
Pediatric simulator: max force	2.1 ± 0.3	2.1 ± 0.5	2.2 ± 0.3
	P = .001	P = .001	P = .001
Adult simulator: mean force	0.4 ± 0.2	0.4 ± 0.1	0.4 ± 0.1
Pediatric simulator: mean force	0.3 ± 0.1	0.3 ± 0.1	0.3 ± 0.1
	P = .02	P = .001	P = .02
Y axis (mean N ± SD) (“in and out” movement)
Adult simulator: total force	11,326 ± 9502	9842 ± 9547	12,635 ± 9496
Pediatric simulator: total force	5399 ± 2599	4866 ± 3720	6413 ± 4657
	P = .03	P = .002	P = .005
Adult simulator: max force	2.6 ± 0.9	2.6 ± 0.9	3.0 ± 0.8
Pediatric simulator: max force	2.9 ± 0.8	2.7 ± 0.9	2.8 ± 0.9
	P = .3	P = .4	P = .6
Adult simulator: mean force	0.3 ± 0.2	0.2 ± 0.1	0.3 ± 0.1
Pediatric simulator: mean force	0.16 ± 0.09	0.17 ± 0.06	0.16 ± 0.06
	P = .02	P = .001	P = .002
Z axis (mean N ± SD) (“up and down” movement)
Adult simulator: total force	14,663 ± 10,716	12,783 ± 10,565	14,965 ± 10,533
Pediatric simulator: total force	9894 ± 4299	9460 ± 5239	10,639 ± 5313
	P = .05	P = .03	P = .04
Adult simulator: max force	4.2 ± 1.2	4.0 ± 1.3	4.5 ± 1.2
Pediatric simulator: max force	3.5 ± 0.7	3.5 ± 0.8	3.4 ± 0.7
	P = .07	P = .01	P = .002
Adult simulator: mean force	0.3 ± 0.2	0.3 ± 0.1	0.3 ± 0.1
Pediatric simulator: mean force	0.12 ± 0.08	0.15 ± 0.08	0.15 ± 0.08
	P = .002	P = .001	P = .001

Comparison of total, maximum, and mean forces used by experts, intermediates, and novices in the performance of a defined intracorporeal suturing task in adult and pediatric laparoscopic simulators.

N, Newtons; SD, standard deviation.

Discussion

The forces generated in the performance of a defined intracorporeal suturing task varied significantly based on simulator size. While force analysis has previously been undertaken,^9,30 this is the first study to compare the forces generated in simulators of differing domain. In this study, total, mean, and maximum forces generated in each of the three axes available were measured during completion of a defined intracorporeal suturing task.

Total and mean forces generated in the X (“side to side”), Y (“in and out”), and Z (“up and down”) axes were significantly higher in the adult laparoscopic simulator, regardless of the level of expertise (novice, intermediate, or expert). These results make intuitive sense as participants seem to recognize that they should use less force in the smaller simulator. This may be due to the decreased domain, but also in part because the participants recognize that the Penrose drain is less securely attached at its base in the smaller simulator: the piece of Velcro attaching the smaller Penrose drain has a smaller surface area, conferring a less secure attachment. The maximum force generated in the X (“side to side”) component was higher in the adult simulator for all expertise levels. This also makes intuitive sense as this defined intracorporeal suturing task involves passing the needle from one side of the Penrose drain to the other, and then tying a surgeon's (double-throw) knot, followed by two single knots. The major axis of force would be expected to be “side to side,” as this is the major axis of motion.

The maximum force generated in the Z (“up and down”) axis was significantly greater for novices and intermediates in the adult rather than the pediatric simulator. Experts did not generate significantly greater maximum forces in this axis. This was not surprising to the senior members of our study group, nor to senior laparoscopic educators: experts seem to maintain the forces in the horizontal plane (X axis) when performing this defined intracorporeal suturing task, while nonexperts exert too much force in the Z (“up and down”) axis, essentially trying to bring the suture closer to themselves. In so doing, they risk avulsing tissue. This is a well-recognized phenomenon among trainees when they begin intracorporeal suturing.

There are other issues which may contribute to the differences in forces generated. They are probably related to pure physical factors such as simulator size, instrument length, and lever effect. There may well be other factors we have yet to even discern. Further study will be required to define and better understand all the factors that impact the forces generated within working spaces of differing domains. Eventually, we hope to deconstruct the task into discrete segments (passage of the needle and pulling of suture through the Penrose drain, followed by a double-throw surgeon's knot, followed by two single-throw knots) and measure the force analysis parameters (FAPs) for each. This may provide insight into which segment of the task generates greatest force, and allow educators and learners to develop strategies to minimize said forces. Future work will also be undertaken to assess extent to which the use of force is within the participant's control by asking them to consciously attempt to minimize the use of force within both simulators, and assessing to what degree they can modulate their use of force.

This pilot study is the first to highlight the differences in forces generated in the performance of a defined task within simulators of differing domain. The educational implications and possible clinical correlations of the different FAPs in the three different axes remain to be determined. Incorporating force analysis into laparoscopic training may help give formative (real-time) feedback, which may improve education and acquisition of technical skills. It will certainly be possible to provide real-time measures for the maximum and mean forces generated within these simulators. The total force in any given axis will be more of a summative method of assessment, as it will require completion of the task before feedback may be provided.

In conclusion, this study demonstrates that adult and pediatric simulators can be enhanced with force sensing capabilities, and that the forces generated in the completion of a defined intracorporeal suturing task vary significantly based on workspace or domain. Forces were greater, particularly in the side-to-side plane, in the larger simulator for participants of all levels in the performance of this defined intracorporeal suturing task. While the clinical and educational implications of this variation in force secondary to workspace volume remain to be established, they do suggest that surgeons adjust the forces generated to the workspace. In certain axes, this seems to be by design, and seems best controlled by experts. In other axes, this seems to be related to the nature of the task, and almost independent of expertise level. A further study is necessary to build on these interesting findings, and tease out the educational and clinical implications.

Limitations

Our analysis, being the first to compare force parameters between large and small simulators, has a number of limitations: While our paired two-tailed t-tests showed significant differences between the means of the adult and pediatric forces, the means themselves were not markedly different, and in some cases the standard deviation (reflecting the spread) overlapped. Even in largely overlapping populations, a statistically significant difference can still be recovered with a large enough sample size, which reduces the variance of the means and allows for smaller differences to be detected, so we expect this accounts for the discrepancy.^31,32 However, this may indicate that the amount of variation is small, and it has not been established what amount of variation in force would have a clinical impact either on tissue or on surgical outcomes.³³ Participants who undertook these tasks were not aware of what was being measured—whether they would have made an effort to, or been able to, reduce their use of force or maximum forces in either box if they knew the measured outcomes are not clear. Further analysis will be undertaken to appreciate how much the use of force can be moderated by participants of varying skill levels. The defined intracorporeal suturing task both is a common one in surgical practice and well validated as a training task, and as such was chosen as the task for this analysis. However, the analysis of force from this single task is thus limited by being only secondary to one task, and cannot be extrapolated freely to other laparoscopic tasks that may require more complex force application.

Footnotes

Acknowledgments

We thank all surgeons, residents, and students who contributed their time to this study, and for their valuable input and expertise.

Disclosure Statement

No competing financial interests exist.

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