The definitive experimental characterization of the frictional and deformational behavior of articular cartilage is a necessary element for the complete understanding of normal and pathological synovial joint function. A new electromechanical instrument, therefore, was utilized to subject cartilage-cartilage interfaces to a set of controlled mechanical, kinematic and environmental conditions in vitro.

Experimental specimens of articular cartilage in situ were derived from conformationally matched bovine humeral head and scapular cup pairs following surgical processing and a geometrical quality control regime. The specially designed instrumentation permitted a spatially fixed test region of the cartilage interface to be loaded and sheared in a steady, continuous or a time dependent manner. The response parameters of cartilage surface shear friction and normal deformation were simultaneously recorded on line by a PdP8/e computer system which automatically sampled, digitized and stored the data continuously during an experiment.

A systematic, comprehensive characterization of the articular cartilage frictional and deformational behavior was performed with the experimental results falling into five general categories:​ 1) the responses to statically applied loads, 2) dynamic loading responses, 3) asymptotic steady-state results, 4) kinematic parameter variation results, and 5) the results of environmental parameter variations. More specifically, the transient and asymptotic responses to static and dynamic loading, shearing velocity variations, dynamic loading frequency effects, start-stop intermittent motion responses, synovial fluid viscosity influences, and buffered saline pH. variations were experimentally documented.

The asymptotic frictional responses of the articular cartilage interfaces to four separate conibinations of loading and fluid environmental conditions were also investigated. Dynamically loaded specimens in bovine synovial fluid yielded the most efficient lubrication with the mean measured coefficient of friction spanning from 0.0019 to 0.0025 across the applied load range. In addition, a nonlinear regression analysis of the frictional and deformational time history relations under static loading was used to construct an emperical model of the transient and steady-state results. Good agreement was obtained between the model predictions and the experimentally observed responses.

Finally, a preliminary investigation of the possible relationship between articular cartilage surface topographical changes and the applied interfacial stress history was conducted. Through the use of scanning electron microscopy and the definitive experimental configuration of the present study it was possible to obtain a significant correlation between the magnitude, duration and direction of the applied mechanical stresses and orientation and degree of the resultant cartilage surface ultrastructural alterations.