Exposure to excessive stress is associated with the pathogenesis of osteoarthritis, a joint disease involved in the degeneration of articular cartilage. Mechanical properties of mature articular cartilage are known to be depth zone-dependent. Although chondrocyte death was observed in articular cartilage after excessive stress loading in vitro, few studies have investigated the correlation between chondrocyte death and local mechanical strains in a depth dependent manner. Here, we developed a real-time observation system of cut cartilage samples under an excessive stress loading (18 MPa) at low (3.5%/s) and high (35%/s) strain rates on the microscope stage, which is regarded as injurious compression in vivo. Using this system, real-time monitoring of local deformations was conducted during compression, and local chondrocyte death was investigated after short-term culture. The results showed that the dead cells were mainly observed in the surface layer at a high strain rate. In contrast, the dead cells were relatively concentrated not in the surface layer but in the middle layer at a low strain rate. The local strain measurements showed that the dead cell distributions were correlated with depth-dependent local strain rates at both low and high strain rates. Moreover, when the surface layer was removed, both depth-dependence in dead cell distributions and in local strain rates disappeared at low and high strain rates. Although the mechanisms underlying mechanically induced osteoarthritis are still elusive, those results suggest a correlation between local chondrocyte death and transient strain rates in a depth dependent manner, and the surface layer played a crucial role in regulating chondrocyte damages and local strains in middle and deep layers. Our study, therefore, could contribute to an analytical understanding of cartilage degeneration under excessive stress loadings.

过度应激与骨关节炎的发病机理有关，骨关节炎是一种与关节软骨退化有关的关节疾病。已知成熟的关节软骨的机械性质取决于深度区域。尽管在体外过度负荷后在关节软骨中观察到软骨细胞死亡，但很少有研究以深度依赖的方式研究软骨细胞死亡与局部机械应变之间的相关性。在这里，我们开发了一种实时观察系统，用于在显微镜载物台上以低应力（3.5％/ s）和高应力（35％/ s）的高应力负荷（18 MPa）切割软骨样品的实时观察系统。体内的伤害性压缩。使用此系统，可以实时监测压缩过程中的局部变形，短期培养后调查局部软骨细胞死亡。结果表明，在高应变率下主要在表层中观察到死细胞。相反，死细胞以较低的应变速率相对集中在表面层而不是中间层。局部应变测量表明，在低应变率和高应变率下，死细胞的分布都与深度相关的局部应变率相关。而且，当去除表面层时，在低和高应变速率下，死细胞分布和局部应变速率的深度依赖性都消失了。尽管机械诱发性骨关节炎的机制尚不清楚，但这些结果表明局部软骨细胞死亡与短暂应变率之间存在深度相关性，表层在调节中，深层软骨细胞损伤和局部应变中起关键作用。因此，我们的研究可能有助于对过度应力负荷下软骨变性的分析理解。