Orthopaedic Soft Tissue Research Program, Hospital for Special Surgery, Research Division 535, East 70th Street, New York, NY 10021.
Orthopaedic Soft Tissue Research Program, Hospital for Special Surgery, New York, NY 10021.
J Biomech Eng. 2022 Sep 1;144(9). doi: 10.1115/1.4054108.
Early stage osteoarthritis is characterized by disruption of the superficial zone (SZ) of articular cartilage, including collagen damage and proteoglycan loss, resulting in "mechanical softening" of the extracellular matrix (ECM). The role of the SZ in controlling fluid exudation and imbibition during loading and unloading, respectively, was studied using confined creep compression tests. Bovine osteochondral (OC) plugs were subjected to either a static (88 kPa) or cyclic (0-125 kPa at 1 Hz) compressive stress for five minutes, and the cartilage deformation and recovery were measured during tissue loading and unloading, respectively. During unloading, the articular surface of the cartilage was either loaded with a small 1% tare load (∼1 kPa) applied through a porous load platen (covered), or completely unloaded (uncovered). Then the SZ (∼10%) of the cartilage was removed and the creep tests were repeated. Randomized tests were performed on each OC specimen to assess variability within and between plugs. Static creep strain was always greater than cyclic creep strain except at the beginning of loading (10-20 cycles). Uncovering the articular surface after creep deformation resulted in faster thickness recovery compared to the covered recovery. Removal of the SZ resulted in increased static and cyclic creep strains, as well as an increase in the cyclic peak-to-peak strain envelope. Our results indicate that an intact SZ is essential for normal cartilage mechanical function during joint motion by controlling fluid exudation and imbibition, and concomitantly ECM deformation and recovery, when loaded and unloaded, respectively.
早期骨关节炎的特征是关节软骨的浅层区（SZ）受到破坏，包括胶原损伤和蛋白聚糖丢失，导致细胞外基质（ECM）的“机械软化”。使用约束蠕变压缩试验研究了 SZ 在分别加载和卸载过程中控制流体渗出和吸收的作用。牛骨软骨（OC）插件分别承受静态（88 kPa）或循环（0-125 kPa，1 Hz）压缩应力 5 分钟，分别测量组织加载和卸载过程中的软骨变形和恢复。在卸载过程中，通过多孔加载板（覆盖）在关节表面上施加小的 1%的皮重（约 1 kPa）（覆盖），或者完全卸载（未覆盖）。然后去除 SZ 并重复蠕变测试。对每个 OC 标本进行随机测试，以评估插件内和插件之间的可变性。除了加载开始时（10-20 个循环）外，静态蠕变应变始终大于循环蠕变应变。与覆盖恢复相比，在蠕变变形后暴露关节表面会导致更快的厚度恢复。SZ 的去除导致静态和循环蠕变应变增加，以及循环峰峰值应变包络增加。我们的结果表明，在关节运动过程中，完整的 SZ 通过控制加载和卸载时的流体渗出和吸收，以及同时控制 ECM 变形和恢复，对于正常软骨的机械功能至关重要。
