Osmotic Effects on the Dynamic Shear Properties of Meniscal Fibrocartilage

The meniscus plays an important role in many biomechanical functions of the knee, including shock absorption, load distribution, and joint lubrication. The ability to perform these functions is determined by the interactions of the major tissue constituents (water, proteoglycan, and collagen), although these interactions have not been as thoroughly studied in fibrocartilage as those in other soft tissues. In articular cartilage, electrochemical interactions between negatively charged glycosaminoglycan (GAG) side chains of proteoglycans and the interstitial fluid generate an osmotic swelling pressure that contributes to the compressive stiffness [1], and proteoglycan degradation dramatically decreases compressive and shear moduli [2]. Although the concentration of proteoglycan in the meniscus is substantially lower (<1%) than that in articular cartilage, aggrecan degradation also greatly decreases the compressive and shear moduli of meniscal fibrocartilage [3]. The proteoglycan distribution in meniscal fibrocartilage is macroscopically heterogeneous [4] and is concentrated in the secondary matrix surrounding the circumferential collagen bundles, and the extent to which osmotic interactions explain the influence on fibrocartilage material properties is unknown. Altering the osmotic strength of the bathing solution supplies a means to control osmotic interactions between the GAGs and the environment without degrading the tissue matrix. The objective of this study was to examine the effects of an altered osmotic environment on the dynamic shear modulus of meniscal tissue.