Concerning the ultrastructural origin of large-scale swelling in articularcartilage

The swelling behaviour of the general matrix of both normal and abnormally softened articular cartilage was investigated in the context of its relatio nship to the underlying subchondral bone, the articular surface, and with r espect to the primary structural directions represented in its strongly ani sotropic collagenous architecture. Swelling behaviours were compared by sub jecting tissue specimens under different modes of constraint to a high swel ling bathing solution of distilled water and comparing structural changes i maged at the macroscopic, microscopic and ultrastructural levels of resolut ion. Near zero swelling was observed in the isolated normal general matrix with minimal structural change. By contrast the similarly isolated softened general matrix exhibited large-scale swelling in both the transverse and r adial directions. This difference in dimensional stability was attributed t o fundamentally different levels of fibril interconnectivity between the 2 matrices. A model of structural transformation is proposed to accommodate f ibrillar rearrangements associated with the large-scale swelling in the rad ial and transverse directions in the softened general matrix.