Cindy Boer

14 | Chapter 1.1 What is osteoarthritis? The first descriptions of osteoarthritis can be traced back to writings of Hippocrates (460-375 B.C.E.)[15]( Figure 1 ). However, from these first writings until the beginnings of the 19 th century, all forms of rheumatic joint diseases, including osteoarthritis, were called “ gout ”. In 1802, William Herben the Elder recognized osteoarthritis as a separate disease for the first time[16]. However, it took until 1889 that John Kent Spender of Bath England coined the name osteoarthritis[17]. The name referring back to the ancient Greek of Hippocrates, where osteo- comes from the Ancient Greek ὀ στέον (ostéon) meaning “bone” and arthritis from the combination of arthr- ἄ ρθρον (árthron) mean- ing “joint, limb” and -itis from ῖ τις(îtis) meaning “pertaining to”, and together forming osteoarthritis: “bone pertaining to the joint/limb”. As implied by the name, osteoarthritis pathology commonly involves the bone, however, we now know that osteoarthritis is a disease of the whole joint ( Figure 2 ). Affecting multiple tissues within the joint, most notably the cartilage and bone, but also the synovium, and possibly the muscles and tendons of the joint[18]. Osteoarthritis is a degenerative disease involving an active and complex process of multiple mechanical, metabolic and inflammatory pathways leading to the destruction and failure of the af- fected joint[19]. the most common and characteristic features of the disease pathology are the degradation of the articular cartilage, together with the formation of new bone, osteophytes, at the margins of the joint. Other known pathological features of osteoar- thritis are bone sclerosis, cartilage lesions, cysts, chondrocalcinosis, and synovial in- flammation. Long has it been thought that osteoarthritis was an inevitable part of aging, that it was a passive “wear-and-tear” disease. However, we now know that osteoarthritis is an active and dynamic disease, an imbalance between the repair and destruction of joint tissue[19]. In addition, osteoarthritis is associated with increased comorbidity and even increased mortality[20]. More and better understanding of the pathological pro- cesses and pathways involved is imperative, if we want to develop treatment strategies for osteoarthritis. The definition of osteoarthritis is based on the pathological effects of the disease on any combination of the tissues involved. Therefore multiple definitions of osteoar- thritis exist. However, the most used definitions are radiographic or clinical osteoarthri- tis. The radiological definition usually consists of the Kellgren-Lawrence grading scale, based on the presence and severity of joint space narrowing (JSN) and osteophytosis (OST)[22], while the clinical definition is focused on the clinical symptoms; pain, swell- ing and stiffness of the joint[23]. Although there is some standardization in osteoar- thritis definitions [24], definitions can still vary per study[25]. Although there is some