DYNAMIC UNCONFINED COMPRESSION OF ARTICULAR-CARTILAGE UNDER A CYCLIC COMPRESSIVE LOAD

To study the effect of dynamic mechanical force on cartilage metabolis m, many investigators have applied a cyclic compressive load to cartil age disc explants in vitro, The most frequently used in vitro testing protocol has been the cyclic unconfined compression of articular carti lage in a bath of culture medium, Cyclic compression has been achieved by applying either a prescribed cyclic displacement or a prescribed c yclic force on a loading platen placed on the top surface of a cylindr ical cartilage disc, It was found that the separation of the loading p laten from the tissue surface was likely when a prescribed cyclic disp lacement was applied at a high frequency. The purpose of the present s tudy was to simulate mathematically the dynamic behavior of a cylindri cal cartilage disc subjected to cyclic unconfined compression under a dynamic force boundary condition protocol, and to provide a parametric analysis of mechanical deformations within the extracellular matrix, The frequency-dependent dynamic characteristics of dilatation, hydrost atic pressure and interstitial fluid velocity were analyzed over a wid e range of loading frequencies without the separation of the loading p laten, The result predicted that a cyclic compressive force created an oscillating positive-negative hydrostatic pressure together with a fo rced circulation of interstitial fluid within the tissue matrix, It wa s also found that the load partitioning mechanism between the solid an d fluid phases was a function of loading frequency, At a relatively hi gh loading frequency, a localized dynamic zone was developed near the peripheral free surface of the cartilage disc, where a large dynamic p ressure gradient exists, causing vigorous interstitial fluid flow. Cop yright (C) 1996 Elsevier Science Ltd