RESUMO
Animal models play a vital role in simplifying the complexity of pathogenesis and understanding the indefinable processes and diverse mechanisms involved in the progression of disease, and in providing new knowledge that may facilitate the drug development program. Selection of the animal models has to be carefully done, so that there is morphologic similarity to human arthritic conditions that may predict as well as augment the effective screening of novel antiarthritic agents. The review describes exclusively animal models of rheumatoid arthritis (RA) and osteoarthritis (OA). The development of RA has been vividly described using a wide variety of animal models with diverse insults (viz. collagen, Freund's adjuvant, proteoglycan, pristane, avridine, formaldehyde, etc.) that are able to simulate/trigger the cellular, biochemical, immunological, and histologic alterations, which perhaps mimic, to a great extent, the pathologic conditions of human RA. Similarly, numerous methods of inducing animal models with OA have also been described (such as spontaneous, surgical, chemical, and physical methods including genetically manipulated animals) which may give an insight into the events of alteration in connective tissues and their metabolism (synovial membrane/tissues along with cartilage) and bone erosion. The development of such arthritic animal models may throw light for better understanding of the etiopathogenic mechanisms of human arthritis and give new impetus for the drug development program on arthritis, a crippling disease.