Cumulative sum: An individualized proficiency metric for laparoscopic fundamentals

A reliable metric of technical proficiency is indispensable to the training of fellows and residents. The purpose of this study was to determine whether cumulative sum (Cusum) has predictive validity in laparoscopic training. We hypothesized that Cusum would be a better predictor of technical ability in fundamentals of laparoscopic surgery (FLS) than traditional practice volume metrics.

Twenty medical students were recruited to practice three FLS tasks: peg transfer, circle cut, and intracorporeal knot tie. Up to 7hours of self-directed practice was allotted to each participant. Practice attempts were scored by standard FLS criteria and monitored via Cusum. Each participant's terminal Cusum performance was analyzed retrospectively. Posttests were conducted by faculty blinded to practice performance.

Eighteen participants completed the study (90%). Median adjusted posttest scores were 102.3, 84.1, and 78.6 for peg transfer, circle cut, and knot tie, respectively. For the knot tie task, participants who exceeded the Cusum decision interval during their final practice attempts performed significantly higher on posttesting (81.2 vs 71.5, p=0.015). Knot tie terminal Cusum score was positively associated with posttest performance after adjusting for practice volume (p=0.031). Total practice volume and practice time were not significantly associated with posttest performance for any FLS task.

Cusum score is a more valid representation of FLS proficiency than practice volume or practice time. Incorporating Cusum in a clinical setting may promote more efficient allocation of time resources and operative volume.