J. Hsu1, J. R. Korndorffer2, K. M. Brown1 1University Of Texas Medical Branch,Surgery,Galveston, TX, USA 2Tulane University School Of Medicine,Surgery,New Orleans, LA, USA
Introduction: Surgical residents develop technical skills at variable rates, often based on random chance of cases encountered. One such skill is tying secure knots without exerting excessive force. Deliberate practice allows more uniform training; however, there are no widely used methods to provide immediate feedback on force exerted as part of deliberate practice training to proficiency. This study describes the design of a simulator using a force sensor to measure instantaneous forces exerted on a blood vessel analog during knot tying, the development of expert derived performance goals, and assessment of novice performance in relation to these goals.
Methods: The knot-tying simulator consists of a Silastic tubing suspended horizontally at a fixed height in a confined space to simulate tying deep in the abdomen, and a Vernier Dual-Range Force Sensor perpendicularly attached to the tubing. Vessel ligations were performed on the tubing with 3-0 Silk sutures at a fixed offset from the sensor location to measure the vertical forces exerted. The offset was corrected by adjusting the sensor reading according to a standard curve created beforehand by a spring scale exerting known fixed forces at fixed offset locations from the sensor. 6 experts (surgical faculty and senior residents) and 8 novices (junior residents) were recruited to each perform 10 vessel ligations (2 square knots each) with two-handed and one-handed techniques. The data were recorded in Vernier Logger Pro software. Internal consistency for each individual’s 10 peak force measurements was tested with Cronbach’s α . Average peak force for novices was compared to experts using Student's t-test.
Results: Cronbach’s α was 0.95. The expert group on average exerted a significantly lower peak force compared to novices and had less variation in peak force across the 10 trials when performing two-handed (0.71±0.36 N vs 1.06±0.4 N, p<0.01) and one-handed (0.82±0.11N vs 1.41±0.36N, p<0.01) vessel ligations. Interestingly, 3 out of the 8 novices performed at force levels equivalent to the expert group average.
Conclusion: We have created a simulator that consistently records peak force data for an individual tying surgical knots, and demonstrates discrimination between novices and experts. Although the expert group performed vessel ligations with significantly lower peak force and less variation than the novice group, there were individuals within the novice group who performed at the expert level. This is consistent with the conceptual framework of milestones, and suggests that the skill of gentle knot tying can be measured and may develop at different chronologic levels of training in different individuals. This simulator can be used as part of deliberate practice curriculum with immediate feedback.