Articular joint mechanics with biphasic cartilage layers under dynamic loading.

The composition and amount of extracellular matrix produced by chondrocytes are thought to be influenced by the stress and strain states in the vicinity of the chondrocytes. During daily activities, such as walking and running, articular joints are loaded dynamically. In the present study, a solution is proposed to simulate the responses of a joint under dynamic loading. In order to show the characteristics of the proposed solution, numerical simulations were carried out, in which the contact radius, the relative approach displacement between the centers of the contacting bodies, or the contact force were controlled. As a result of the history-dependent material properties of the articular cartilage, the predicted parameters changed nonperiodically, when the controlled parameters varied periodically. For a constant load, the contact radius and the relative displacement between the contacting bodies were predicted to increase at decreasing rates. When the contact force was varied dynamically, the predicted mean values of the contact radius, the relative displacement between the contacting bodies, and the contact pressure at the center of the contact area depended on the amplitude and the duration of the loading. When the relative displacement between the contacting bodies was controlled, the amplitudes and the cycling frequency must be limited to avoid a loss of contact between the articular joint surfaces. The proposed solution is valid for a long but limited time period, the exact extent of which is yet to be determined. It can be used to simulate the effects associated with cartilage degeneration in diseases such as osteoarthritis.