Epidemiology of osteoarthritis

Osteoarthritis (OA) is a progressive multifactorial disease that not only leads to articular cartilage loss and joint space narrowing, but also to pain, loss of function and physical disability, thus greatly impairing quality of life. The concept of the pathology of OA has evolved from being viewed as cartilage-limited to a multifactorial disease affecting the whole joint. Indeed, all the joint tissues including capsule, ligament, tendons, menisci, subchondral bone, synovium, muscle, and neurological structure are intricately implicated in the disease pathology. This chapter will review, from an epidemiological point of view, the classification and radiological definition of osteoarthritis, its socioeconomic burden, the prevalence of radiographic and symptomatic hand, knee and hip OA, and finally the local and systemic risk factors. Introduction: Osteoarthritis from past to present Not many diseases can claim to have a history as rich and ancient as osteoarthritis (OA). From prehistoric times to the present day, OA has proven to be a most challenging disease. OA can be traced back in time from paleopathological findings in skeletal remains, historical depictions, and more Correspondence/Reprint request: Dr. Frédéric Massicotte, Osteoarthritis Research Unit, University of Montreal Hospital Research Centre (CRCHUM), Notre-Dame-Hospital, Montreal, Quebec, Canada H2L 4M1 E-mail: frederic.massicotte@gmail.com Frédéric Massicotte 2 recent pathological concepts. In fact, OA is frequently referred to as the oldest known disease on the planet. Indeed, evidence of its presence can be found in dinosaur skeletons of up to 70 million years old [1]. Some more controversial reports even describe the first example of OA in the spine of a 200 million year old Dimetrodon [2]. Osteoarthritis stigmata can be found in nearly every period and civilization, such as in the Neanderthal [3] and CroMagnon skeletons [4], Egyptian mummies [5], and more recent skeletal remains from England [6]. The pathological changes in a 100 million year old bone and a contemporary bone are remarkably similar, suggesting that OA is impervious to evolution [7]. As eloquently reviewed by Buchanan et al. [8], despite the nearly ubiquitous presence of the disease throughout evolution, clinicians did not recognize OA until the late 18 century, possibly due to the disease showing few obvious clinical signs. The first report of this disease in the literature may be found in Heberden’s notice of “Digitorum Nodi” in 1782, which was not published until 1802. In the “Commentaries on the History and Cure of Diseases” in 1793 Heberden the Elder described what is now called Heberden’s node with a clear distinction from gout [9]. Further nomenclature confusion delayed the recognition of OA, and OA and rheumatoid arthritis were even considered the same entity, known as arthritis deformans. It was not until 1859, when Alfred Baring Garrod proposed the name rheumatoid arthritis, that a distinction was made between these two diseases [10]. From an epidemiological perspective, the historical reference to OA is controversial, due in large part to the terminology used and the confusion between primary and secondary OA, as well as mimickers such as gout and rheumatoid arthritis. Today, nomenclature debates persist between osteoarthrosis, degenerative bone disease, and osteoarthritis, reflecting the different ideologies on the importance of inflammation in the pathophysiology of OA. However, evidence of the critical role of inflammation in OA is overwhelming and is discussed in Chapter 4 Proteinase-activated receptor-2: an attractive DMOAD target for the treatment of osteoarthritis. Classification of osteoarthritis Considering the high prevalence and socioeconomic impact of OA, welldesigned fundamental and clinical studies are of the utmost importance. One of the first steps toward reproducible studies is universally accepted classification criteria. It may seem trivial, but these criteria are continually evolving, for example with the creation of different radiographic scoring systems, which make study comparison a real challenge. To date, the most widely accepted classification criteria are those of the American College of Epidemiology of osteoarthritis 3 Table 1. American College of Rheumatology criteria for classification of osteoarthritis. Rheumatology (ACR). As shown in Table 1, the ACR has classified OA into two broad categories: idiopathic, which can be localized or generalized, and secondary [11]. Secondary OA may further be classified as post-traumatic, congenital, or due to calcium deposition disease or other bone/systemic diseases. As shown in Table 2, specific classification criteria for the hand, hip and knee were also proposed by the ACR, and these criteria are currently used for OA definition in the vast majority of clinical studies [11-13]. Frédéric Massicotte 4 Table 2. American College of Rheumatology criteria for osteoarthritis of the hand, hip and knee. Items required for OA presence