Figure 1.

Plowing as a source of surface tractional forces in articulating tissues (modified from previously published work; Mow et al., 1993). Loading of the articular surfaces causes pressurization of the fluid phase of the cartilage matrix. As a static load is maintained, compression of the cartilage occurs as fluid moves laterally along the hydraulic gradient. If lateral movement of the stress-field occurs, further pressurization of the fluid phase of the matrix occurs ahead of the encroaching stress-field because the porosity of the matrix limits the velocity of the fluid phase. The result is a “bow wave” and plowing forces produced by the pressurized fluid within the cartilage.