In musculoskeletal joint systems, many diagnosis and treatment modalities depend on the biomechanical data of the tissues and the structures involved. Image-based models of the structure and the materials involved can facilitate the determination of these data through computational biomechanics. This chapter will present the state-of-the-art development of this emerging technology together with several selected application examples in order to demonstrate its exciting potential in medical research, education, and patient care. It is our intention to stimulate collaborations in the field for the refinement of this technology and to explore other applications.

Medical technology has gone through two distinct periods of evolution during the 20th century—from the industrialization age to the imaging and informatics era. The new discipline of bioengineering established between these two periods served as the catalyst in fostering the transition, putting new technology and science on firm and rational grounds in the medical arena. As we march into the new century carrying with us the available knowledge and know-how, we stand at the threshold of the most exciting time in comparison to the explosion of biological sciences during the past two decades. New medical innovations based on the engineering technology may be the solution to allow biological research advances to be effectively disseminated into practical, reliable, and affordable clinical applications. Biomechanicians have been working on quant-itating the hard and soft tissue mechanical properties, muscle and joint forces, and bone stress/strain under both static and

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dynamic loading conditions; but rarely were the analyses performed in parallel and interactively, nor could we see the results together with realistic models depicting the system response through animation. With the help of the new imaging and computational advancements, we now are able to achieve the goal of "visualization of biomechanical computations". Difficult modeling problems associated with the human musculoskeletal system can be solved using the visual guide and simulation approach through a hybrid reality environment. Many known and unknown loading conditions now can be created on the models to test their responses with unprecedented clarity and reliability. This new bioengineering technology using image-based models and the biomechanical computation has been utilized to perform (1) noninvasive determination of connective tissue mechanical properties; (2) musculoskeletal structural modeling and analysis; (3) computer-aided surgical planning; (4) joint replacement implant and bone fracture fixation device design and evaluation, and (5) rehabilitation exercise assessment and optimization.

Visualization and medical imaging have rapidly emerged as unique and significant advancement in recent history of medical diagnostics and therapeutic intervention. The input data of the human organ structure can be obtained from CT, MRI, PET, SPECT, ultrasound, confocal microscopy, etc. The early development and utilization of such technology was restricted to image acquisition and visualization, in both two and three dimensions. The 3D graphic models of human organ systems provide the ideal tools for surgical skill training with realistic anatomical shape, surface texture, and tactile feedback. Only recently, the qualitative visualization has progressed to quantitative modeling with the ability to simulate physiologic function and in vivo biomechanics of musculoskeletal joint systems — a four-dimensional model simulation.

The purpose of this chapter is to introduce the image-based biomechanical models and the associated computational techniques to quantitate material properties and to perform static, dynamic, and stress analyses while allowing results to be visualized through simulation and animation. Combined with the environment and loading simulation, a virtual laboratory with computerized human musculoskeletal models and the material constitutive relationship can be created on workstations to allow repeated testing and analyses under unlimited variations of loading conditions and pathological involvements. The real-time graphical animation of these models will be a powerful tool for education, surgical skill training, and basic scientific research involving musculoskeletal disability effects, joint deformity or degeneration correction, multiple trauma management, and the patients' functional outcome prediction associated with a variety of orthopedic treatments. The validity of such application depends upon model verification using anatomic specimens properly loaded on testing machines or on joint dynamic simulators. Our ability to identify and exploit the appropriate and reliable applications of this technology will help to rationalize this landmark breakthrough in bioengineering.

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