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Contact stress in a whole joint bioreactor : intrinsic levels & augmentation by external loading


A whole joint bioreactor was recently described as an ex vivo apparatus for studying the biomechanical regulation of cartilage metabolism in knee joints [17]. Stimulation of chondrocyte lubricant biosynthesis by continuous passive motion (CPM) of knee joints was hypothesized to be due to cartilage responses to compressive and shear stresses [18]. In the whole joint bioreactor setup, compressive stress within the joint at the cartilage surfaces in the passive state is unknown. The objective of this study was to assess the distribution and magnitude of contact stress within knee joint preparations. The results show significant effects of angle and load magnitude on contact stress and force within the joint. Near full extension, the anterior regions of the LFC exhibited high stress levels, and these generally correspond to regions found previously to respond biologically to CPM. These results provide biomechanical measures and methods to test the role of such cartilage contact stresses in a whole joint bioreactor. Previously, no methods were available to apply loads externally to manipulate cartilage compressive stress in the whole joint bioreactor. The objective of this study was to examine the effects of axial and patellar loading as possible biomechanical stimulation methods for use in joint-scale bioreactors. Contact stress magnitude and location and overall joint force were increased significantly by both axial and patellar loading. These results suggest that such an approach could also be used to study effects of mechanical loading of knee joints with repair procedures, such as implanted tissue grafts, under controlled loading conditions

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