[Osteoarthritis. Etiology, typing, staging and histological grading]

Degenerative disorders of the musculoskeletal system, in particular osteoarthritis, are among the most common diseases of the elderly and their importance in an aging society is continuously increasing. Correspondingly, many surgical interventions are undertaken and pathological specimens submitted for histopathologic workup. The pathophysiology of osteoarthritis, which ultimately leads to joint destruction, is still poorly understood. The question remains as to whether the cause lies (mainly) within the chondrocytes themselves (e.g. cellular aging/senescence) or whether the synovial membrane or the subchondral bone are equally or even more important factors. The process of joint destruction can be evaluated in terms of pathogenesis (typing), extent (staging) and degree of the most extensive focal damage (grading). Because of the heterogeneity of the disease and substantial individual differences in progression, classification and grading of cartilage degeneration represents a complex task. Any pathology report should be concise and delineate only the essential features. Differentiating between primary osteoarthritis and secondary degenerative changes, e.g., due to previously unknown rheumatoid disease, bone necrosis or an infection of the joint, is of particular clinical interest.