Localized cystic areas may develop in the subchondral bone, leading to structural weakening. All of these changes usually are accompanied by little synovial reaction, in sharp contrast to the synovial changes typical of rheumatoid arthritis. At times, there may be hypertrophy of synovial tissues, but histologic study usually reveals primarily fibrous tissue, with minimal infiltration of inflammatory cells and little proliferation of synovial lining cells. Synovial fluid from osteoarthritis patients typically does not reveal evidence of inflammation. Viscosity and mucin clot tests are normal.
Mononuclear cells are predominant.
The hemoglobin concentration, white blood cell count, erythrocyte sedimentation rate, and levels of protein, glucose, and complement are also normal.