Quantification of Chondrocyte Death and Proteoglycan Content in Mechanically Impacted Articular Cartilage

Abstract

Impact injuries can lead to cellular and matrix changes in articular cartilage, similar to those occurring in the pathenogenesis of secondary osteoarthritis. The purpose of this study was to examine the changes in cartilage following an impact injury as a model for early osteoarthritic degradation. Using an in vitro organ culture model, the proteoglycan content and the viability of chondrocytes relative to the magnitude of an impact injury, the time following the injury and the relative location within the cartilage layer was examined. In this study, it was hypothesized that injurious mechanical loading would result in increased chondrocyte death and decreased proteoglycan content with increasing load and time in culture. Paired porcine knee joints were obtained fresh and patellae were removed using sterile techniques. A total of 36 patellae were used. Twelve patellar cartilage specimens were subjected to controlled mechanical injuries to a force level of 1000 N (medium) and 12 specimens at a force level of 2000 N (high). Twelve patellae were used as non-injured controls. Following impaction, the intact patellae were placed in organ culture for 0, 3, 7 or 14 days and subsequent degenerative changes over time were assessed. Cell viability was quantified using a MTT (3,(4,5-dimethylthiazoyl-2-yl) 2,5(diphenyl-tetrazolium bromide) assay and the percentage of dead cells at various positions was determined. Proteoglycan concentration was measured using Safranin-O staining intensities. There was a significant, location dependent, cell death increase with increasing impact load. A significant location dependent decrease in proteoglycan content was observed from medium impactions, while an increase in proteoglycan content was seen from high impactions. In conclusion, the magnitude of an impact load can significantly affect the degree of matrix changes throughout the depth of articular cartilage tissue over time.