Background: To observe the sequence of chondrocyte degeneration and matrix degradation in the superficial surface cartilage of the tibial plateau in guinea pigs with spontaneous knee osteoarthritis (OA). Methods: Sixty guinea pigs were euthanized at the ages of 8 months (n = 20),10 months (n = 20) and 12 months (n = 20) respectively. The degree of degeneration of the tibial plateau cartilage was evaluated by Osteoarthritis Research Society International (OARSI) score. The levels of Aggrecan,CollagenX,MMP-13 and Caspase-3 in the chondrocytes were detected by immunohistochemistry (IHC). The serum concentration of CTX-II was measured and compared. Western blot analysis was used to detect the levels of Aggrecan,CollagenX,MMP-13 and Caspase-3 in the cartilage tissue. Results: The OARSI scores both in 8-month-old group and 10-month-old group were lower than that in the 12-month-old group. The levels of Aggrecan in articular chondrocyte were higher both in 8-month-old group and 10-month-old group than that in 12-month-old group. The level of Collagen X increased with the age of guinea pigs. And the levels of MMP-13 and caspase-3 both in 10-month-old group and 12-month-old group were higher than those in 8-month-old group. The concentration of CTX-II in serum increased significantly in 12 months old group. Conclusion: The superficial chondrocytes of the tibial plateau first appeared to be hypertrophic and then apoptotic, and the matrix was further degraded when spontaneous knee osteoarthritis occurred in guinea pigs. Changes in the physiological state of chondrocytes are the initiating factors in the pathogenesis of knee OA.

This cross-sectional study aimed to investigate whether the infrapatellar fat pad (IPFP) mediates the relationship between environmental exposures and clinical symptoms in patients with knee osteoarthritis (KOA). A total of 108 participants with KOA were included in this study, and environmental exposure data, including temperature, wind speed, and relative humidity, were obtained from local meteorological records. IPFP characteristics were quantitatively assessed using 3.0T magnetic resonance imaging (MRI), including morphometric and signal intensity (SI) parameters. Clinical symptoms were evaluated using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Principal component analysis (PCA) was used to reduce dimensionality of IPFP MRI features. Mediation analysis was performed to examine whether IPFP parameters mediated the effect of environmental exposures on WOMAC scores. PCA revealed that SI parameters accounted for 56.87 % of the total variance in IPFP features, while morphometric parameters explained 16.65 %. Correlation analysis showed that most SI parameters (e.g., mean SI, SD SI) were significantly associated with WOMAC scores (ranging from r = 0.20 to 0.49, p < 0.05), in contrast to morphometric measures. Environmental exposures, particularly lower temperatures, higher wind speed, and daily weather changes, were significantly correlated with increased SI. Mediation analysis demonstrated that IPFP MRI parameters, particularly SI parameters, significantly mediated the effects of environmental exposures on pain and total WOMAC scores. The IPFP, particularly its SI characteristics, mediates the relationship between environmental exposures and clinical symptoms in KOA.