Task Decomposition of Laparoscopic Surgery for Objective Evaluation of Surgical Residents' Learning Curve Using Hidden Markov Model

Objective: Evaluation of the laparoscopic surgical skills of surgical residents is usually a subjective process carried out in the operating room by senior surgeons. The two hypotheses of the current study were: (1) haptic information and tool/tissue interactions (types and transitions) performed in laparoscopic surgery are skill-dependent, and (2) statistical models (Hidden Markov Models—HMMs) incorporating these data are capable of objectively evaluating laparoscopic surgical skills.Materials and Methods: Eight subjects (six residents—two first-year (R1), two third-year (R3), and two fifth-year (R5)—and two expert laparoscopic surgeons) performed laparoscopic cholecystectomy on pigs using an instrumented grasper equipped with force/torque (F/T) sensors at the hand/tool interface, and F/T data was synchronized with video of the operative maneuvers. Fourteen types of tool/tissue (T/T) interactions, each associated with unique F/T signatures, were defined from frame-by-frame video analysis. HMMs for each subject and step of the operation were compared to evaluate the statistical distance between expert surgeons and residents with different skill levels.Results: The statistical distances between HMMs representing expert surgeons and residents were significantly different (α < 0.05). Major differences occurred in: (1) F/T magnitudes; (2) type of T/T interactions and transitions between them; and (3) time intervals for each T/T interaction and overall completion time. The greatest difference in performance was between Rl (junior trainee) and R3 (midlevel trainee). Smaller changes were seen as expertise increased beyond the R3 level.Conclusion: HMMs incorporating haptic and visual information provide an objective tool for evaluating surgical skills. Objective evidence for a “learning curve” suggests that surgical residents acquire a major portion of their laparoscopic skill between year 1 and year 3 of training.