Rheological effects of synovial fluid on nutritional transport

Synovial fluid is an excellent source of nutrients for the cells of the car tilage, through which water and other solutes like glucose are permeable. I t has long been established that the tissue imbibes and exudes fluid when d eformed, metabolities are believed to move to and from the cells through th e ground substance by mechanical effects and by diffusion. Local variation of the permeability within the articular cartilage plays an important role in nutritional transport. To account for the effects of structural configur ation of tissue, rate, depth and amount of solute penetration, we have mode lled the cartilage by mixture of two distinct constituents, i.e., an incomp ressible fluid phase and an incompressible porous solid phase. It is observ ed that when local permeability decreases, the concentration decreases. Whe n fluid Rows into the cartilage due to metabolism, the solid portion of the porous matrix increases. Due to the increased solidity of the cartilage ma trix. less fluid enters into the cartilage and nutritional transport decrea ses. In the case of diseased joints the nutritional transport is very diffi cult, owing to increased rigidity or local variation of permeability within the cartilage. The concentration distribution at the same depth in articul ar cartilage for low-molecular-weight solutes is less than that for high-mo lecular-weight solutes. Thus, for low-molecular-weight solutes. the phenome non of nutrition transport is diffusion dominated whereas for high-molecula r-weight solutes, it is dominated by mechanical pumping action. The paper f urther concludes that in the process of imbibition and exudation, the cells of the middle area of the cartilage surface get more nutrition as compared to the cells at the periphery, so the earliest signs of cartilage degenera tion appear in the unstressed areas. Therefore joint motion is assumed nece ssary for cartilage nutrition. It also concludes that as the viscoelastic p arameter increases, the concentration decreases in the articular cartilage so that the cells of the cartilage get less nutrition and can deteriorate.