11Update on the epidemiology, risk factors and disease outcomes of osteoarthritis
Introduction
Osteoarthritis (OA) is the most common form of arthritis worldwide and a major cause of disability in middle-age and older adults [1]. The most frequently affected joints are the hip, knee, hand, foot and spine, although OA can affect any joint. It is estimated that symptomatic OA affects one in eight men and women in the US (27–31 million) [1], [2], and worldwide, it is estimated that 250 million people have knee OA [3]. OA is an important cause of disability, with hip and knee OA accounting for 17 million years lived with disability or 2.2% of all-cause years lived with disability [3], [4]. OA is linked to substantive economic costs estimated in developed countries to be between 1% and 2.5% of GDP [5], [6]. The bulk (85%) of the direct costs of OA treatment are due to the costs of joint replacement surgery [7]. In the UK, there were over 185,000 primary hip and knee replacements performed in 2016, with the number set to increase substantially related in part to the ageing population [8], [9].
Although cartilage loss remains the signature pathological feature of OA, it is currently recognised that OA is a disease of the whole joint, with pathological changes in the bone, the soft tissues including synovium, menisci and ligaments. OA may be characterised as primary if there is no identifiable underlying cause and secondary if there is an underlying cause or significant triggering event such as prior trauma. The main symptoms of OA include pain, stiffness and loss of function. There is, however, discordance between the presence of symptoms and radiographic change, and many people with radiographic OA (up to 50%) do not have associated symptoms [10]. The reason for this apparent discordance is unclear, although it is likely in part because plain radiography is an insensitive indicator of the structural and nociceptive changes that occur in OA.
OA can be classified on the basis of radiographic criteria alone or combination criteria including symptoms and radiographic changes (symptomatic OA). The most widely used radiographic criteria are the Kellgren-Lawrence method, which characterises disease as one of the five grades (0–4) based on the presence of joint space narrowing, osteophytes and sclerosis of the subchondral bone [11]. There are, however, limitations related in part to inconsistencies in scoring and also the reliance on the presence of osteophytes, and other criteria have been developed on the basis of scoring of individual radiographic features of the disease [12].
Section snippets
Prevalence
Most of the published data on prevalence derive from population-based radiographic surveys. Plain radiographs are insensitive to early disease, and therefore, these studies tend to underestimate disease occurrence. In a survey of individuals with neither radiographic signs nor symptoms of OA, by magnetic resonance imaging, a more sensitive indicator of joint damage, abnormalities thought to be associated with knee OA were detected in 89% of cases [13]. Estimates of the occurrence of OA vary in
Incidence
Using data from the Fallon Community Health Plan, a health maintenance organisation in Central Massachusetts, among adults aged 20–89 years, the age- and sex-standardised incidence of knee OA was 240/100,000 person years, hip OA was 88/100,000 person years and hand OA was 100/100,000 person years [21]. Incidence increased with age, however, with a levelling off or decline at older ages (>80 years) and with rates greater in women than in men, especially after the age of 50 years [21]. Data from
Lifetime risk
Using data from the Johnston County OA project, it is has been estimated that 40% of adults from the age of 45 years will develop symptomatic hand OA by the age of 85 years for those who live up to that age; this is similar to the corresponding risk of symptomatic knee OA (45%), though greater than that for hip OA (25%) [23], [24], [25]. Using data based on self-report, however, from the US National Health Interview Survey, the lifetime risk of symptomatic knee OA from the age of 25 years was
Influence of race and ethnicity
There are ethnic differences in the occurrence of OA. European and American data do not appear to differ markedly in the occurrence of disease for hand, knee and hip OA [27]. Chinese men and women have a lower prevalence of both radiographic and symptomatic hand OA and radiographic hip OA than Caucasians [28], [29]. The prevalence of radiographic knee OA, however, is similar in Chinese and Caucasian men, whereas prevalence of both radiographic and symptomatic knee OA appears to be greater in
Secular change
With the demographic change to a more elderly population, the number of people with OA is set to increase. Such demographic change is likely to be compounded by the increase in the prevalence of obesity, which is a major risk factor for the disease. Data from Canada suggest that the numbers of people with OA will increase from 4.4 million in 2010 to 10.4 million in 2040 [42]. More recent data from Sweden suggest an increase in clinically diagnosed OA (any site) from 26.6% in 2012 to 29.5% in
Summary
OA is the most frequent form of arthritis and a leading cause of pain and disability. The prevalence of OA increases with age, and the number of people affected is set to increase because of increasing life expectancy. There is important variation in the frequency of OA in different racial and ethnic groups, which may provide clues to the pathogenesis of the disease. Genetic and environmental factors including obesity and trauma are important determinants of disease. The use of validated PROMs
Conflicts of interest
The authors have no conflicts of interest.
Funding
No funding to declare.
References (157)
- et al.
Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010
Lancet
(2012) - et al.
Disability-adjusted life years (DALYs) for 291 diseases and injuries in 21 regions, 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010
Lancet
(2012) - et al.
Economics of osteoarthritis: a global perspective
Bailliere's Clin Rheumatol
(1997) - et al.
Health economics in the field of osteoarthritis: an expert's consensus paper from the European society for clinical and economic aspects of osteoporosis and osteoarthritis (ESCEO)
Semin Arthritis Rheum
(2013) - et al.
Future projections of total hip and knee arthroplasty in the UK: results from the UK Clinical Practice Research Datalink
Osteoarthritis Cartilage OARS Osteoarthritis Res Soc
(2015) - et al.
The effect of osteoarthritis definition on prevalence and incidence estimates: a systematic review
Osteoarthritis Cartilage OARS Osteoarthritis Res Soc
(2011) - et al.
One in four people may develop symptomatic hip osteoarthritis in his or her lifetime
Osteoarthritis Cartilage OARS Osteoarthritis Res Soc
(2010) - et al.
Differences in radiographic features of knee osteoarthritis in African-Americans and Caucasians: the Johnston county osteoarthritis project
Osteoarthritis Cartilage OARS Osteoarthritis Res Soc
(2009) - et al.
Racial differences in self-reported pain and function among individuals with radiographic hip and knee osteoarthritis: the Johnston County Osteoarthritis Project
Osteoarthritis Cartilage OARS Osteoarthritis Res Soc
(2009) - et al.
Current and future impact of osteoarthritis on health care: a population-based study with projections to year 2032
Osteoarthritis Cartilage OARS Osteoarthritis Res Soc
(2014)