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A survey of some of the advances made over the past 10 years in the understanding of joint mechanics by the Niigata biomechanics researchers are presented. We have conducted research on joint mechanics with an awareness that approaches from both experimental and mathematical analysis are important. Topics covered in this chapter include: measurement of joint contact pressure under experimental conditions using a pressure-sensitive conductive rubber sensor which we have developed; and mathematical analysis of joint contact, in particular, using the anisotropic cartilage model that introduces the idea of a specific alignment for collagen fiber.

Acoustic emission (AE) may be defined as the elastic stress waves generated by microcracks, dislocation movements, etc. during loading in a material. The AE from bone under loading was first reported by Hanagud et al. in 1973 [1], and other reports on the AE properties of bone have been published [2,3]. The aim of this study is to identify the influence of osteoporosis on the fracture mechanism of vertebral bodies using the AE method. We performed quasi-static compression tests on eight osteoporotic lumbar vertebrae and determined stiffness and maximum load from load-deformation curves. Simultaneously, AE from the vertebral body during the compression test was measured by an AE sensor, and the AE, event count rate and AE energy distribution were analyzed. We herein discuss the relationship between the fracture mechanism of vertebrae and AE involving various grades of osteoporosis, which was determined by the value of bone mass density (BMD) and by X-ray findings.

A technique based on the new definition of 6 degree-of-freedom motion parameters has been developed to improve the applicabihty of biomechanical joint motion analysis to chnical estimation. Two methods of define femoral translation and rotation angle are used to analyze motion data for the Genesis total knee arthroplasty (TKA) knee with the 6 degree-of-freedom electric goniometer and biplanar computed radiography (CR) X-ray system. One method is obtained from the virtual contact point located in the femoralsagittal plane, and the other corresponds to the screw displacement vector. It was found that the discrepancy between the current and conventional motion analysis is insignificant.

Utilizing an original goniometer system and biplanar X-ray methods, the three-dimensional (3-D) knee motion after total knee arthroplasty (TKA) was analyzed. Seven patients who underwent Yoshino-Shoji (Y/S) total knee arthroplasty and who had no complaints in their daily activity and could walk without any support were studied. The mean follow-up period of this current study was 32 months after surgery. Chnical and radiological assessments were also evaluated. The following measurements were performed for this study: active knee motion (nonweight and with 1kg weight), level walking, and going up and down stairs. In active knee motion (nonweight), two types of tibial translation, anterior or posterior, were seen with knee flexion less than 70°. At flexion greater than 70°, all knees showed anterior tibial translation. The result of gait analysis showed no double knee action and diminished flexion angle in swing phase. Going up or down stairs showed a basically similar motion pattern, but knee flexion and extension differed when going down stairs. At more than 70° knee flexion, the tibia moved forward by quadriceps muscle tension. This result demonstrates that quadriceps muscle power is important for compensation of posterior cruciate ligament (PCL) resection. Lack of normal rollback motion, however, will lead to stress concentration and is the cause of wear and loosening of the tibial component.

Painful arthritis around the radial styloid is induced in scapholunate advanced collapse of the wrist (SLAC). This change also occurs in non-union of the scaphoid and in triscaphe arthrodesis.