Role of chondrocytes in the development of osteoarthritis.

The chondrocyte holds a key position in the development of osteoarthritis. As the only living element of the articular cartilage, it produces the components of the matrix, i.e., collagens and proteoglycans. In the course of its life, the chondrocyte is susceptible to nutrient and toxic dangers. This leads to a qualitative and quantitative jeopardy of the matrix production. Collagens and proteoglycans are also subject to metabolic influences. Whatever the cause(s), osteoarthritis results in deficient masking of the collagen fibers and in roughening of the cartilaginous surface. Thus, the phase of "wear and tear" is initiated, which is characteristic of osteoarthritis. This process may provoke a total loss of cartilage and opening of the subchondral medullary spaces. However, osteoarthritis probably only becomes clinically manifest when a secondary synovitis supervenes, which is caused by mediators developing from degradation products of the cartilaginous matrix. Thus, osteoarthritis can be considered to develop from a disproportion between the quality of the matrix and load to the cartilage. Aside from avoiding non-physiologic overload to the articular cartilage, therapy must influence the secondary synovitis. Furthermore, an attempt should be made to interfere effectively with the chondrocytic metabolism by means of "chondroprotective substances."