Theory Of Fluid Lubrication Of Hydrogels And Articular Cartilage During Compression Under An Applied Load
A fluid lubrication model for articular cartilage was put forward by Mc Cutchen, in which a high percentage of the load is supported by fluid pressurization in the interface region separating the two cartilage coated surfaces as the cartilage is compressed under load. This reduces the friction by reducing the percentage of the load which is carried by solid material in the cartilage. For two bones which are in contact in a healthy joint, which are each coated by a layer of cartilage whose thickness is much smaller than its lateral dimensions, it will be argued that since the bone is impervious to fluid flow in healthy joints, almost all of the fluid that is expressed from the cartilage under load flows through the interface region, where it supports part of the load. This is in contrast to previous theoretical and in vitro experimental studies of this problem, in which most of the fluid does not flow into the interface. It is shown that for mean asperity height small compared to a length scale (which depends on the cartilage or hydrogel permeability, the fluid viscosity and the dimensions of the cartilage or hydrogel) a large percentage of the load is supported by fluid pressurization.