In situ Measurement of Cadaveric Soft Tissue Mechanical Properties and Fulcrum Forces for Use in Physics-Based Surgical Simulation

Development of a realistic surgery simulator that delivers high fidelity visual and haptic feedback, based on the physics of deformable objects, requires the use of empirical data on the behavior of soft tissues when subjected to external loads. Measurements on live human patients present significant risks, thus making the use of cadavers a logical alternative. Cadavers are widely used in present day surgical training, are relatively easy to procure through excellent donor programs and have the right anatomy, which makes them better candidates for training than the porcine model. To investigate the static and dynamic properties of soft tissue, we have developed a high precision tactile stimulator by modifying an exisitng haptic interface device, the Phantom, and used it to record the force-displacement behavior of intra-abdominal organs of fresh human cadavers at the US Surgical in Connecticut and Albany Medical College. Another paraemeter of great practical significace, but mostly overlooked in the literature, is the fulcrum force at the point of entry of the trocar into the abdomen. The length of the surgical tools, coupled with a thick abdominal wall of overweight or obese patients, tend to produce torques at the wrist of the surgeon which are often large enough to mask any haptic sensation from the organs being operated on. To ascertain the true role of haptics in endoscopic surgery one needs to measure these fulcrum forces. In this paper we discuss techniques and some preliminary results in this direction.