Objective Assessment of Surgical Skills

Minimally invasive surgery (MIS) involves a multi-dimensional series of tasks requiring a synthesis between visual information and the kinematics and dynamics of the surgical tools. Analysis of these sources of information is a key step in mastering MIS but may also be used to define objective criteria for characterizing surgical performance. The BlueDRAGON is a new system for acquiring the kinematics and the dynamics of two endoscopic tools synchronized with the visual view of the surgical scene. It includes passive mechanisms equipped with position and force torque sensors for measuring the position and the orientation (P/O) of two endoscopic tools along with the force and torque (F/T) applied on them by the surgeon’s hands. The analogy between Minimally Invasive Surgery (MIS) and human language inspires the decomposition of a surgical task into its primary elements in which tool/tissue interactions are considered as “words” that have versions pronunciations defined by the F/T signatures applied on the tissues and P/O of the surgical tools. The frequency of different elements or “words” and their sequential associations or “grammar” both hold critical information about the process of the procedure. Modeling these sequential element expressions using a multi finite states model (Markov model – MM) reveals the structure of the surgical task and is utilized as one of the key steps in objectively assessing surgical performance. The surgical task is modeled by a fully connected, 30 state Markov model representing the two surgical tools where each state corresponds to a fundamental tool/tissue interaction based on the tool kinematics and associated with unique F/T signatures. In addition to the MM objective analysis, a scoring protocol was used by an expert surgeon to subjectively assess the subjects’ technical performance. The experimental protocol includes seven MIS tasks performed on an animal model (pig) by 30 surgeons at different levels of training including expert surgeons. Analysis of these data shows that the major differences between trainees at different skill levels were: (a) the types of tool/tissue interactions being used, (b) the transitions between tool/tissue interactions being applied by each hand, (c) time spent while performing each tool/tissue interaction, (d) the overall completion time, and (e) the variable F/T magnitudes being applied by the subjects through the endoscopic tools. An objective learning curve was defined based on measuring quantitative statistical distance (similarity) between MM of experts and MM of residents at different levels of training. The objective learning curve (e.g. statistical distance between MM) was similar to that of the subjective performance analysis. The MM proved to be a powerful and compact mathematical model for decomposing a complex task such as laparoscopic suturing. Systems like surgical robots or virtual reality simulators in which the kinematics and the dynamics of the surgical tool are inherently measured may benefit from incorporation of the proposed methodology for analysis of efficacy and objective evaluation of surgical skills during training.