Cindy Boer

General Introduction | 15 1.1 ▲ Figure 2: Characteristics of an osteoarthritic joint . A) Schematic overview of a healthy articular joint. B) Schematic overview of characteristics and structural changes in a joint affected by osteoarthritis. Any combination of these changes can be seen in an osteoarthritic joint. Figure adapted from[21]. standardization in osteoarthritis definitions [24], definitions can still vary per study[25]. Also, as osteoarthritis is a heterogenous disease, involving many pathological pathways all leading to the same outcome, subgroups with distinct pathology are possibly unrec- ognized. All contributing to heterogeneity and complexity of osteoarthritis research. The complexity of osteoarthritis Osteoarthritis is a complex multifactorial disease. Not just because it has had a turbu- lent and long history or that the pathology affects multiple tissues of the whole joint. Osteoarthritis is a complex disease in the scientific sense, where complex means: both genetic and environmental factors play an important role in the development of the dis- ease. Multiple environmental risk factors have been recognized for osteoarthritis, with age, physical activity and obesity as the most well-established risk factors[21]. The complex interplay between the different environmental risk factors them- selves and with the underlying genetic risk factors, determines an individual’s risk for developing osteoarthritis. Mostly from twin studies we have learned that the predicted