CHARACTERIZATION OF CARTILAGE METABOLIC RESPONSE TO STATIC AND DYNAMIC STRESS USING A MECHANICAL EXPLANT TEST SYSTEM

A new mechanical explant test system was used to study the metabolic r esponse (via proteoglycan biosynthesis) of mature, weight-bearing cani ne articular cartilage subjected to static and dynamic compressive str esses. Stresses ranging from 0.5 to 24 MPa were applied sinusoidally a t 1 Hz for intervals of 2-24 h. The explants were loaded in unconfined compression and compared to age-matched unloaded explants. Both stati c and dynamic compressive stress significantly decreased proteoglycan biosynthesis (range 25-85%) for air loading time intervals. The inhibi tion was proportional to the applied stress but was independent of loa ding time. After rehydration upon load removal, the measured water con tent of the loaded explants was not different from the unloaded explan ts for all test variables. Autoradiographic and electron microscopic a nalysis of loaded explants showed viable chondrocytes throughout the m atrix. Our results suggest that the decreased metabolic response of cy clically loaded explants may be dominated by the static component (RMS ) of the dynamic load. Furthermore, the observed decreased metabolism may be more representative of the in situ tissue response than that of unloaded explants, in which we found an increasing rate of metabolism for up to 6 days after explant removal. Copyright (C) 1996 Elsevier S cience Ltd.