<s>[INST] What is the difference between osteoarthritis and arthritis? [/INST] Osteoarthritis is initially characterised by a loss of joint cartilage, which thins and eventually ends up affecting the bone that forms part of the joint (subchondral bone). There may be some degree of inflammation in osteoarthritis, but this is much less evident than in rheumatoid arthritis. Osteoarthritis is much more common than rheumatoid arthritis and has a clear association with age, being a disease that is predominantly seen in people of more than 45-50 years of age. It causes joint pain that occurs mainly after the joint has been in use (mechanical pain) and which tends to subside when the joint is rested. In rheumatoid arthritis, however, the synovial inflammation occurs first, and cartilage and subchondral bone may be affected later on. The type of joints affected, the characteristics of the pain, the clinical evolution, and the treatment is very different for rheumatoid arthritis compared to osteoarthritis.  Source: Clinic Barcelona. Link: https://www.clinicbarcelona.org/en/assistance/diseases/rheumatoid-arthritis/frequently-asked-questions. Field: Rheumatology. Disease: Arthritis </s>