CHONDROCYTE DEFORMATION AND LOCAL TISSUE STRAIN IN ARTICULAR-CARTILAGE - A CONFOCAL MICROSCOPY STUDY

It is well accepted that mechanical forces can modulate the metabolic activity of chondrocytes, although the specific mechanisms of mechanic al signal transduction in articular cartilage are still unknown. One p roposed pathway through which chondrocytes may perceive changes in the ir mechanical environment is directly through cellular deformation. An important step toward understanding the role of chondrocyte deformati on in signal transduction is to determine the changes in the shape and volume of chondrocytes during applied compression of the tissue. Rece ntly, a technique was developed for quantitative morphometry of viable chondrocytes within the extracellular matrix using three-dimensional confocal scanning laser microscopy. In the present study, this method was used to quantify changes in chondrocyte morphology and local tissu e deformation in the surface, middle, and deep zones in explants of ca nine articular cartilage subjected to physiological levels of matrix d eformation. The results indicated that at 15% surface-to-surface equil ibrium strain in the tissue, a similar magnitude of local tissue strai n occurs in the middle and deep zones. In the surface zone, local stra ins of 19% were observed, indicating that the compressive stiffness of the surface zone is significantly less than that of the middle and de ep zones. With this degree of tissue deformation, significant decrease s in cellular height of 26, 19, and 20% and in cell volume of 22, 16, and 17% were observed in the surface, middle, and deep zones, respecti vely. The deformation of chondrocytes in the surface zone was anisotro pic, with significant lateral expansion occurring in the direction per pendicular to the local split-line pattern. When compression was remov ed, there was complete recovery of cellular morphology in all cases. T hese observations support the hypothesis that deformation of chondrocy tes or a change in their volume may occur during in vivo joint loading and may have a role in the mechanical signal transduction pathway of articular cartilage.