CHONDROCYTE DEATH IN ARTICULAR CARTILAGE DUE TO EXCESSIVE MECHANICAL LOADING IN THE AXIAL AND TRANSVERSE DIRECTIONS

摘要

Chondrocyte injury and death in articular cartilage can cause matrix degradation and is a risk factor for secondary osteoarthritis Chondrocyte death can occur due to excessive mechanical loading, such as with a single high traumatic impact load (≥20 MPa), repeated sub-impact loads (≥5 MPa), or extensive cyclic loads (≥1 MPa) Several recent studies have shown that Chondrocyte death depends not only on the stress magnitude but also on the stress rate, strain rate and load duration. In a previous study we showed that chondrocytes in the superficial zone were most vulnerable to mechanical stress. However, whether stress (stress rate) or strain (strain rate) caused the cell death is still unclear. This is because the local matrix strain and stress are related, the matrix response is biphasic (transient), and the tissue microstructure is inhomogeneous. In articular cartilage, the superficial zone has the lowest compressive modulus and will deform as much as twenty-five times more than that of the middle and deep zones under axial. Since a highly inhomogeneous strain distribution exists in the tissue when the matrix is loaded, it is difficult to determine whether chondrocytes in the different zones have the same ability to resist an excessive mechanical strain. However, a transverse load from the side of articular cartilage can generate a relatively homogenous strain field across the explant. The objective of this study was to measure the cell death in articular cartilage under a uniform strain (loading transversely) and a uniform stress (loading axially). We hypothesized that cell death would be uniformly distributed in the matrix in the transverse loaded condition, as compared to the axially loaded condition, and that the Chondrocyte death is due primarily to applied strain and not to stress.