Summary of the effects of celecoxib on osteoarthritis in vivo (animal and human). Celecoxib has different in vivo effects in the different tissues of the osteoarthritic knee joint. In cartilage celecoxib has a positive effect on proteoglycan content, as well as an inhibiting effect on several mediators of inflammatory and cartilage destruction processes. In synovial tissue celecoxib shows inhibiting effects on cytokines and the number of synovial macrophages. Celecoxib shows a positive effect on trabecular bone volume and a negative effect on bone resorption and the number of osteoclasts in subchondral bone. COX, cyclooxygenase; iNOS, inducible nitric oxide synthase; MMP, matrix metalloproteinase; NO, nitric oxide; PGE2, prostaglandin E2.