Virtual reality orthopedic surgery simulator

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Abstract

This paper describes a highly interactive virtual reality orthopedic surgery simulator. The simulator allows surgeons to use various surgical instruments to operate on virtual rigid anatomic structures, such bones, prostheses and bone grafts, to simulate every procedure on the rigid structures for complex orthopedic surgeries, including arthroplasty, corrective or open osteotomy, open reduction of fractures and amputation. A comparative study of the simulator with paper simulation was performed and showed that interns and residents found the simulator to be a useful learning tool, and that visiting doctors could use it effectively for planning verification and rehearsal of operations.

Introduction

Orthopedic surgeries usually involve complex geometry and require awareness of topology changes in skeletal morphology. Current training methods for interns and residents in teaching hospitals do not adequately raise spatial perception about geometry and topology changes of skeletal morphology. Two reasons for the inability are trainees can only observe an operation before he participates in a surgery and preoperative rehearsal usually involves 2D (two dimensional) paper surgical simulations based on X-ray images. Moreover, orthopedic visiting doctors may also fail in real operations even after evaluating topology and geometry changes on rigid bones, prostheses and bone grafts of all procedures by 2D paper simulations. The failure rates were reported as 10–20% for high tibia osteotomy [1], [2], [3] and 5–15% for anterior fusion of the spine [4], [5], [6], [7], [8], [9]. These failures, including poor anatomic section lines, poor contact surfaces, inappropriate size and shape of bone graft and improper reduction position, are caused by insufficient spatial data from the 2D paper simulations. (Soft tissues on healing and open-up are usually not evaluated before a surgery because surgeons can easily open and close up soft tissues and modify soft tissues to obtain satisfactory shapes during the surgery [2], [8].)

The application of virtual reality (VR) to surgical training gives a more realistic human machine interaction than traditional 2D simulations and has already become a useful surgical planning and training tool. Several VR surgical simulators have been developed which provide detailed information regarding simulated tissues, tools and actions of surgeons [10]. Simulation systems usually provide a virtual environment by rendering a surface model that may be reconstructed from video data (for simulating endoscopic or laparoscopic surgery, e.g. Satava [11]), X-ray projections (for bone surgery, e.g. Caponetti [12]), transversal tomographic slices (for arthroscopic or oral implant surgery [13], [14]), or synthetic surfaces (for ophthalmic surgery [15]). However, the surface model is difficult to employ for computing topology changes on anatomic structures because no interior information is available. In contrast to surface models, a volume (stack of parallel 2D grayscale images) model represents a body via regularly positioned cuboids (voxels) and is suitable to convey relations between adjacent tissues or structures with a high accuracy (with resolution limits but without projection errors [16]), and to simulate surgeries with topology changes [17]. Volume manipulation algorithms can easily simulate topology changes of structures such as structure removal, section and fusion (local manipulations) [17], [18], however, are still insufficient in simulating global manipulations such as a structure reposition and distant fusion, and in identifying a new-sectioned structure. These manipulations are also necessary in orthopedic surgeries.

This paper describes an (VR) orthopedic surgery simulation system based on volume data. The system can compute geometric and topologic changes on bones, prostheses and bone grafts of every orthopedic procedure and provide stereographic images (a pair of 3D images for two eyes) of the simulation results. Through the 3D visual input and output environment, the stereographic images allow surgeons to obtain a spatial perception of every procedure. We have been using this system in preoperative meetings to verify the surgical modality and to simultaneously train and educate residents and internsin our orthopedic department. This paper is structured into several parts. Section 2 introduces current volume-based orthopedic surgical simulation methods and describes their limitations. Section 3 introduces our methods and the structure of our prototype system. Section 4 introduces the kinds of orthopedic surgeries that our system can simulate and shows some simulation examples. Section 5 describes a comparative study between the computer simulations and paper simulations to show the performance of the VR orthopedic simulator. Conclusions and future study are introduced in Section 6.

Section snippets

Volume-based orthopedic surgery simulators

Many excellent algorithms have been developed for visualizing a volume. For example, tissue surfaces can be well approximated by hundreds of thousands of triangulated isosurfaces at the sub-voxel level (e.g. [19]). These isosurfaces can be quickly rendered even by general PC platforms with smooth shading models such as the Gouraud shading model. Instead of manipulating triangulated isosurfaces, surgical simulation algorithms usually manipulate voxels directly to simulate surgeries especially

Software

The software system including the simulator software and the driver software was developed in Chung Yuan Christian University, Chung-Li, Taiwan. The system was first reported in 1996 [20], and has since been modified, improved and used to train interns and residents, and to rehearse the surgical plans for visiting doctors in the Orthopedic Department of Taipei Medical University Hospital. The software is implemented in C++ (Visual C++ ver. 5.0) using the OpenGL libraries to render isosurfaces

Complicated orthopedic surgery simulations

Surgeons can use this system to simulate procedures on rigid bones, prostheses and bone grafts in orthopedic surgeries such as arthroplasty, corrective or open osteotomy, fusion, open reduction for complicated fractures and amputation via the simulation functions outlined above. In the following, we explain how to use the simulation functions to simulate the surgeries. The exercises of the simulation functions implemented on one knee arthroplasty, one open osteotomy and one fusion are

Comparative study between VR simulations and paper simulations

From July 1997–June 1998, a number of surgeries are simulated simultaneously using the VR computer system and the traditional paper surgery methods by a group of surgeons. We compared the results of the paper and computer simulations to know which method give more real, precise and preferable results and is easy to use.

Discussion and future works

Simulators must achieve a useful degree of realism for a corresponding surgery. Our simulation methods can manipulate voxel-represented structures of bones, prostheses and bone grafts to model interactions between the structures such as: cutting, fusing, repositioning, recognition, and collision testing of a moving structure. By these functions, our system can simulate complex geometry and topology changes of skeletal morphology for every orthopedic procedure. These capabilities are necessary

Summary

Computed tomography (CT) or magnetic resonance imaging (MRI) scanning has become a standard procedure to reveal interior anatomies. Visualizing a volume constituted by transversal slices can ease observation of anatomies to improve diagnoses. Beyond the volume visualization, manipulating volume data to simulate deformation or topology changes of tissues during a surgery can verify surgical plans, rehearse procedures and predict prognoses. In the presented work, an additional link is deleted or

Acknowledgements

The authors would like to thank the National Science Council for financial support of this research under Contract No. NSC-86-2213-E-033-036, NSC-87-2213-E-033-005, NSC-89-2320-B-038-019-M08 and NSC-89-2213-E-033-070. We would also like to thank all of our colleagues at the computer research lab, the visiting doctors, residents and interns at our orthopedic department for participation in the study. We also like to thank the Radiology Department of Taipei Medical University Hospital for

Ming-Dar Tsai received the BS degree in Mechanical Engineering from National Taiwan University, Taipei, Taiwan, in 1983, and MS and Ph.D. degrees in Machinery Precision Engineering from the University of Tokyo, Tokyo, Japan, in 1988 and 1991, respectively. Since 1991, he has been on the faculty of the Department of Information and Computer Engineering, Chung Yuan Christian University, Chungli, Taiwan, where he is currently an Associate Professor. His research interests include computer

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    Ming-Dar Tsai received the BS degree in Mechanical Engineering from National Taiwan University, Taipei, Taiwan, in 1983, and MS and Ph.D. degrees in Machinery Precision Engineering from the University of Tokyo, Tokyo, Japan, in 1988 and 1991, respectively. Since 1991, he has been on the faculty of the Department of Information and Computer Engineering, Chung Yuan Christian University, Chungli, Taiwan, where he is currently an Associate Professor. His research interests include computer graphics, virtual reality, scientific visualization and computer in medical applications.

    Ming-Shium Hsieh received the MD degree in Medicine from Taipei Medical College, Taiwan, in 1974, and the Ph.D. degree in Orthopedic Surgery from Essen University, Essen, Germany, in 1982. Since 1986, he has been on the faculty of the Department of Orthopedics at Taipei Medical College, Taipei, Taiwan, where he is currently the Chairman and an Associate Professor. His research interests inclue image studies and orthopedic field including spine surgery, arthroplasty and traumatology.

    Shyan-Bin, Jou is a Ph.D. student at Chung Yuan Christian University. He received the BS degree in Civil Engineering from Chung Yuan Christian University and MS degree in Computer and Information Science from New Jersey Institute of Technology in 1984, 1990, respectively. Since 1991, he is a lecturer at Nanya Institute of Technology, Chungli, Taiwan. His research interests include computer graphics and image processing.

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