Force model for laparoscopic graspers: implications for virtual simulator design.

INTRODUCTION: Laparoscopic graspers limit haptic perception, which in turn leads to tissue damage. Using virtual simulators to train surgeons in handling these instruments would ensure safer grasp. The design of a laparoscopic virtual simulator with force feedback depends on effective implementation of the grasper force model. OBJECTIVE: To develop a laparoscopic grasper tip force model theoretically from grasper mechanics and validate the same experimentally during laparoscopic pinching. MATERIALS AND METHODS: We developed a force model for double and single jaw action graspers using grasper mechanics. For experimental validation, the handle angle and the forces at the tip and the handle of the instrumented graspers during laparoscopic pinching of porcine abdominal tissues were measured. The intra-class correlation coefficient (ICC) between experimental and calculated tip force was calculated. RESULT: Excellent ICC (ICC ≥0.8, p<.001) between calculated and experimental tip force was obtained for both graspers for all grasped tissues. Mean absolute forces for all trials while using double and single jaw action graspers were ((FTc = 1.7N, FTe = 1.8N) and (FTc = 2.2N, FTe = 2.8N)) for gall bladder, ((FTc = 3.4N, FTe = 4.4N) and (FTc = 3.3N, FTe = 3.4N)) for liver and ((FTc = 4.2N, FTe = 4.5N) and (FTc = 2.3N, FTe = 2.6N)) for spleen, respectively. CONCLUSION: The proposed model may be used for the design of laparoscopic pinching action in a virtual simulator with force feedback and also for better ergonomic design of laparoscopic graspers.

Factors influencing forces during laparoscopic pinching: Towards the design of virtual simulator.

BACKGROUND: The design of good virtual simulators for laparoscopic training requires realistic visual and tactile perception. This is a study to characterize the factors that contribute to forces during laparoscopic pinching. METHODS: Surgeons were divided into four groups according to years of experience in laparoscopic surgery. They were asked to grasp six different types of porcine abdominal tissue in a randomly sequenced manner, using two different types of sensorized graspers, under two regimes of perceptual feedback (with and without visual feedback). The forces (grasper handle force and grasper tip force) and grasper handle angle were recorded and analyzed. RESULTS: The factors that determine forces during laparoscopic pinching can be ranked as follows: surgical experience (p < .001), tissue type (p = .007) and visual feedback (p = .033), but not grasper type (p = .071). Handle force depends significantly on surgical experience (p < .001), tissue type (p = .001) and visual feedback (p = .019), but not on grasper type (p = .203). Tip force depends significantly on surgical experience (p < .001) and marginally on tissue type (p = .082) and visual feedback (p = .053) but not on the grasper type (p = .180). CONCLUSION: Forces during laparoscopic pinching depend on surgical experience, tissue type and presence of visual feedback but not on grasper type. Our data can be an input in the design of virtual simulators with force feedback, for training laparoscopic pinching.