Matrix and cell injury due to sub-impact loading of adult bovine articularcartilage explants: effects of strain rate and peak stress

Mechanical overloading of cartilage has been implicated in the initiation a nd progression of osteoarthrosis. Our objectives were to identify threshold levels of strain rate and peak stress at which sub-impact loads could indu ce cartilage matrix damage and chondrocyte injury in bovine osteochondral e xplants and to explore relationships between matrix damage, spatial pattern s of cell injury, and applied loads. Single sub-impact loads characterized by a constant strain rate between 3 x 10(-5) and 0.7 s(-1) to a peak stress between 3.5 and 14 MPa were applied, after which explants were maintained in culture for four days. At the higher strain rates, matrix mechanical fai lure (tissue cracks) and cell deactivation were most severe near the cartil age superficial zone and were associated with sustained increased release o f proteoglycan from explants. In contrast, low strain rate loading was asso ciated with cell deactivation in the absence of risible matrix damage. Furt hermore, cell activity and proteoglycan synthesis were suppressed throughou t the cartilage depth, but in a radially dependent manner with the most sev ere effects at the center of cylindrical explants. Results highlight spatia l patterns of matrix damage and cell injury which depend upon the nature of injurious loading applied. These patterns of injury may also differ in ter ms of their long-term implications for progression of degradative disease a nd possibilities for cartilage repair. (C) 2001 Orthopaedic Research Societ y. Published by Elsevier Science Ltd. All rights reserved.