Effect of impact load on articular cartilage: Development of an intra-articular fracture model

Objectives: To investigate the biological and mechanical effects of a single-impact load on articular cartilage. Design: An in vitro laboratory study was performed using mature bovine cartilage and bone, and isolated cartilage explants. Each specimen was impacted with a single load applied with a specially designed impactor and materials test machine. Chondrocyte metabolic activity and cartilage structural integrity was investigated using force displacement curves, radionuclide labeling, histology, and changes in water content. Setting: Laboratory for Soft Tissue Research, New York, New York, U.S.A. Specimens: Viable mature bovine cartilage and cartilage and bone explants. Main Outcome Measurements: Mechanical failure, proteoglycan synthesis, water content, histology, radiography, and scanning electron microscopy changes occurring during the twenty-four-hour period immediately following impact. Results: Force/displacement curves for the cartilage and bone explants demonstrated two failure-stress peaks, the first at fifty megapascals, representing cartilage failure, and a second peak at seventy-five megapascals, 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 greater 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-energy impact load.