Background: During surgery, all joints of the upper limbs, including shoulder, elbow, wrist, and finger, coordinate to complete a task. Hence, analysis of these joint movements during surgical manipulations is useful for the design of optimal hand-instrument interface. This study compared two types of surgical handheld manipulators with 6 degrees of freedom with different handle designs: one using a controlling wheel (fingertip control, FTC) and the other with a controlling joint (master slave control, MSC) in terms of ergonomics and movement efficiency.
Methods: Seventeen subjects consisting of surgeons and medical students participated in the experiment. Each performed two standardized surgical tasks in a surgical simulator. A set of reflective markers were attached on the subjects' upper limbs and the marker positions during the tasks were collected by a motion capture system for subsequent analysis of the trunk, shoulder, elbow, wrist, and fingers joint movements. The subjects also completed a Visual Analogue Scale-based questionnaire on their preference for the control mechanism and ease of handling.
Results: The data showed that the manipulator with the MSC was more difficult to handle and resulted in larger range of movements, higher velocities, and accelerations in some joints than the manipulator with FTC mechanism. Use of the MSC manipulator also was accompanied by a higher error rate. Additionally, the subjects preferred the finger actuated manipulator and gave it a higher Visual Analogue Score for maneuverability.
Conclusions: The manipulator equipped with the MSC was ergonomically inferior; it was more difficult to handle and provided less precision, resulting in higher error rates than the FTC manipulator. This study also confirmed that motion analysis is useful for assessment of the design of handheld manipulators for endoscopic surgery.