The design of simulators for surgical training and planning poses a great number of technical challenges. Therefore the focus of systems and algorithms was mostly on the more restricted minimal invasive surgery. This paper tackles the more general problem of open surgery and presents efficient solutions to several of the main difficulties. In addition to an improved collision detection scheme for computing interactions with even heavily moving tissue, a hierarchical system for the haptic rendering has been realized in order to reach the best performance of haptic feedback. A flexible way of modeling complex surgical tools out of simple basic components is proposed. In order to achieve a realistic and at the same time fast relaxation of the tissue, the approach of explicit finite elements has been substantially improved. We are able to demonstrate realistic simulations of interactive open surgery scenarios.