EFFECT OF IMPACT LOAD ON ARTICULAR-CARTILAGE - DEVELOPMENT OF AN INTRAARTICULAR FRACTURE MODEL

Objectives: To investigate the biological and mechanical effects of a single-impact load on articular cartilage. Design: An in vitro laborat ory study was performed using mature bovine cartilage and bone, and is olated cartilage explants. Each specimen was impacted with a single lo ad applied with a specially designed impactor and materials test machi ne. Chondrocyte metabolic activity and cartilage structural integrity was investigated using force displacement curves, radionuclide labelin g, histology, and changes in water content. Setting: Laboratory for So ft Tissue Research, New York, New York, U.S.A. Specimens: Viable matur e bovine cartilage and cartilage and bone explants. Main Outcome Measu rements: Mechanical failure, proteoglycan synthesis, water content, hi stology, radiography, and scanning electron microscopy changes occurri ng during the twenty-four-hour period immediately following impact. Re sults: Force/displacement curves for the cartilage and bone explants d emonstrated two failure-stress peaks, the first at fifty megapascals, representing cartilage failure, and a second peak at seventy-five mega pascals, representing bone failure. Fine grain radiographs, histology, and scanning electron microscopy all confirmed the destruction of the cartilage in the area of direct impact (zone I) and subchondral bone failure and the detachment of the cartilage within the lesser impacted area (zone IT). Proteoglycan synthesis was reduced significantly (p < 0.05) in the areas of direct impact (zone I) compared with areas with less or no impact (zones II and III, respectively). Significantly gre ater water content (p < 0.05) was found within the cartilage of zone I compared with zones II and III. Conclusions: Significant and possibly irreversible articular cartilage damage occurs after a single high-en ergy impact load.