Figure 4.

Impact-induced chondrocyte death differs by location within the joint. (A) Chondrocyte death is correlated with impact magnitude. Cell death was positively correlated with peak impact stress for both the MFC (r² = 0.70, p <0.0001) and the PFG (r² = 0.79, p <0.001). Data presented is for all impacts performed throughout the study. (B) Chondrocytes from the patellofemoral groove (PFG) were more sensitive to impact-induced cell death than the medial femoral condyle (MFC). At lower impact magnitudes (M1) MFC viability was not affected. Groups that do not share a letter are significantly different at p <0.05. Error bars, ±s.d. (C and D) Representative images of PFG cartilage stained for live cells (green) with calcein AM and dead cells (red) with ethidium homodimer and imaged in cross-section using confocal microscopy. The articular surface is toward the top of the images. (C) Un-impacted control cartilage had less dead (red) staining than (D) lower impacted (M1) and (E) higher impacted (M2) in PFG explants.