Research On The Tendon Modeling Techniques In Virtual Anterior Cruciate Ligament Reconstruction

In recent years, computers have been more and more widely used in various fields of social life, with the development of computer science and technology. Virtual reality (VR) is the simulation of real world using computer. Virtual surgery system is one of the most important applications of Virtual reality in modern medicine. Simulation of ropy objects or similar objects is widely used in Virtual surgery systems. So the simulation technology of ropy objects based on the physical deformation model, is greatly valuable to improve the whole system's reality and enhance the immersion for users. The key of ropy objects simulation is to maintaining three aspects: the visual realism, the physical properties and the efficiency of calculation. With the background of tendon simulation in virtual"ACL"reconstruction surgery system, this paper studied the problem of ropy object simulation. The followings are the main contributions of this paper.1. We propose a ropy object model based on modified mass-spring model. The model modifies the linear relationship of flexibility force and deformation which can efficiently reduce the"super-flexible"phenomenon. And the deformation stress of the model is more authentic than basic mass-spring model. The calculation complexity of our method is nearly the same as the basic mass-spring model.2. We propose and implement a ropy objects collision pre-detection and pre-response algorithm. Firstly, we establish the expanding bounding boxes of ropy objects'cylinders. Secondly, we establish hierarchical bounding box tree of AABB with expanding bounding boxes as leafs. Thirdly, we pre-detect the collision between ropy objects and self-collision by traversing AABB. Fourthly, we add temporary penalty spring to pre-respond collisions that pre-detected. This algorithm can efficiently simulate the collision detection and response without real tangency, and can avoid"puncture"phenomenon.3. We propose and implement a simulation method of human tendon. In the geometric model layer, the tendon is composed with reference points (or masses) and cylinders. In the medical model layer, we establish ropy object model based on modified mass-spring model. In the collision model layer, we establish AABB tree with expanding bounding boxes as leaves to pre-detect and pre-respond collision. In the rendering stage, points at all layers on the grid are mapped to appropriate location according to masses'positions in the geometric model. This method suits most simulation of ropy objects.We implement the tendon simulation module in the virtual"ACL"reconstruction surgery system with VC++6.0. The results show that the module can simulate various tendon actions, and can meet the system's requirement of visual realism, physical characteristic and real-time.