Forces of Tool-Tissue Interaction to Assess Surgical Skill Level

Abstract

Importance: The application of optimal forces between surgical instruments and tissue is fundamental to surgical performance and learning. To date, this force has not been measured clinically during the performance of microsurgery.

Objectives: To establish a normative catalog of force profiles during the performance of surgery, to compare force variables among surgeons with different skill levels, and to evaluate whether such a force-based metric determines or differentiates skill level.

Design, Setting, and Participants: Through installation of strain gauge sensors, a force-sensing bipolar forceps was developed, and force data were obtained from predetermined surgical tasks at the Foothills Medical Centre, University of Calgary, a tertiary care center that serves Southern Alberta, Canada. Sixteen neurosurgeons (3 groups: novice, intermediate, and experienced) performed surgery on 26 neurosurgical patients with various conditions. Normative baseline force ranges were obtained using the force profiles (mean and maximum forces and force variability) from the experienced surgeons. Standardized force profiles and force errors (high force error [HFE], low force error [LFE], and force variability error [FVE]) were analyzed and compared among surgeons with different skill levels.

Main Outcomes and Measures: Each trial of the forceps use was termed successful or unsuccessful. The force profiles and force errors were analyzed and compared.

Results: This study included 26 patients (10 [38%] male and 16 [62%] female; mean [SD] age, 43 [15] years) undergoing neurosurgery by 16 surgeons (6 in the novice group, 5 in the intermediate group, and 5 in the experienced group). Unsuccessful trial–incomplete significantly correlated with LFE and FVE, and unsuccessful trial–bleeding correlated with HFE and FVE. The force strengths exerted by novice surgeons were significantly higher than those of experienced surgeons (0.74 vs 0.00; P < .001), and force variability decreased from novice (0.43) to intermediate (0.28) to experienced (0.00) surgeons; however, these differences varied among surgical tasks. The rate of HFE and FVE inversely correlated with surgeon level of experience (HFE, 0.27 for novice surgeons, 0.12 for intermediate surgeons, and 0.05 for experienced surgeons; FVE, 0.16 for novice surgeons, 0.10 for intermediate surgeons, and 0.05 for experienced surgeons). The rate of LFE significantly increased in intermediate (0.12) and novice (0.10) surgeons compared with experienced surgeons (0.04; P < .001). There was no difference in LFE between intermediate and novice surgeons. Stepwise discriminant analysis revealed that combined use of these error rates could accurately discriminate the groups (87.5%).

Conclusions and Relevance: Force-sensing bipolar forceps and force analysis may help distinguish surgeon skill level, which is particularly important as surgical education shifts to a competency-based paradigm.

Figure 1.. Force Data Recorded by SmartForceps for 3 Surgical Types of Tasks

A, Four strain gauges are attached to the lateral surface of the bipolar forceps prongs for sensing coagulation (closing) and dissection (opening) forces. The strain gauges were covered with medical-grade sterilizable tape, and the forceps was steam autoclaved before clinical use. B-D, Examples of forces recorded for coagulation (arrowheads indicate closing) (B), division (arrowheads indicate opening and closing) (C), and dissection (arrowheads indicate opening) (D).

Figure 2.. Representative Force Data and Definition of Force Errors

A and B, Representative force data from an experienced (A) and a novice (B) surgeon for the same surgical task and case (coagulation of sphenoid ridge meningioma). The forces from the novice surgeon varied (circled variable peak forces), whereas the experienced surgeon applied forces uniformly. C, The definition of force errors based on experienced surgeons’ data. The fifth and 95th percentile of the maximum forces and 95th percentile of the coefficient of variation (CV, arrow) of forces for all trials from experienced surgeons were selected for the cutoff values. FVE indicates force variability error; HFE, high force error; and LFE, low force error.

Figure 3.. Comparison of Standardized Force and Rates of Error Between Successful and Unsuccessful Trials and Among Surgeon Groups

Standardized mean, maximum, and coefficient of variation (CV) of force (A and C) with rates of error (B and D). In A and C, the horizontal lines within the box represent the mean force values; the black squares, medians; and the error bars, SDs. FVE indicates force variability error; HFE, high force error; and LFE, low force error. ^aP < .01. ^bP < .05.

Figure 4.. Error Rates and Scores for the 3 Groups of Surgeons

A-C, Radar chart for the 3 groups of surgeons showing error rates. D, Scatterplot of the canonical scores from stepwise discriminant analysis for the 3 groups of surgeons. The x signs indicate the center of the ellipses. For stepwise discrimination analysis data used to construct the scatterplot, see eTable 5 in the Supplement. DF indicates discriminant function; FVE, force variability error; HFE, high force error; and LFE, low force error.