講演タイトルおよび講演内容 ：

Title: On the Mechanobiology of Joint Degeneration

Abstract: During early development of the joint, a local environment of shear stress is preferred for bone formation, while hydrostatic stresses are more conducive to maintaining cartilage tissue. We propose that the degenerative breakdown of the joint tissues also involve similar mechanobiological factors. In osteoarthritis for example, our recent finding of primary bone formation in a pre-osteoarthritic joint, found to be related to micro-to-nanoscale tissue structural changes, highlights the role of mechano-structural factors in the pathophysiology of the joint. Importantly therefore, to determine critical levels of stresses and strains that are involved in joint physiology, for both the joint's development or demise, the complexities of tissue structure and its load-bearing mechanics would need to be addressed. In this talk, our multiscalar interpretations of cartilage-bone structural response to load are presented with a view of elucidating previously unaddressed subtleties of tissue mechanics and joint degeneration.

Title: Design considerations for the deep flexion knee implant: what can we learn from natural knee biomechanics?

Abstract: There is still much to be done to improve the design of knee implants both in terms of longevity and their ability to serve a wider range of patient needs. The increasing medical needs of aging Asian populations (in which deep knee bending and squatting are common activities of daily living) presents the call for better design in implants that will allow deep flexion to be performed safely and reliably, without affecting the expected longevity of the implant. In order to provide the design rationale for an appropriate knee implant, a more in-depth knowledge of the kinematics and kinetics of deep knee flexion in the natural knee is crucial. The author has conducted several studies to investigate the biomechanics of the natural knee in squatting and the data and analyses from these studies form the basis for this talk. From gait studies it was found that in Asian-style squatting the knee flexes up to 150_ and the tibiofemoral contact forces are as high as 3 to 4 times bodyweight. Translating the contact forces into stresses, in-vitro studies on human cadaver knees showed that the peak pressures can be as high as 20 MPa as a result of the drastic reduction in contact area.  Coupled with high stresses, the external rotation of the femur about the tibia ranged from 10_ to 20_. The extent of this rotation was attributed to the unique morphology of the medial versus lateral tibial plateaus. The study also highlights an additional important kinematic feature of knee bending found in the subjects studied that has received little attention in the literature. In descending and ascending from a squat there were significant shear forces in the tibiofemoral joint that underwent rapid reversal from being posteriorly directed to anteriorly directed. This rapid reversal, if incorporated into simulated loadings of implants in in-vitro materials testing systems, may provide further insight into mechanisms of implant failure typically attributed to deep flexion knee activity.