An update on the pathogenesis and epidemiology of osteoarthritis

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Definition of osteoarthritis

Also called degenerative joint disease and osteoarthrosis (because of the inconsistency of inflammation), osteoarthritis is a disease of the whole joint in which all articular structures are affected. Early in the disease, the pathologic events are dynamic. Injured cartilage mounts an attempt at increased matrix synthesis and repair while exuberant osteophytes stabilize the joint, preventing injurious instability. Clinically, a person with an episode of osteoarthritic joint pain may begin a

Structural versus symptomatic disease

Evidence of radiographic osteoarthritis is generally defined as the presence of definite osteophytes in a joint. Symptomatic osteoarthritis, like clinical osteoarthritis, is usually defined as the presence of joint pain or other joint discomfort along with evidence of radiographic disease [6].

Almost everyone has structural evidence of osteoarthritis on radiographs or MR imaging in at least one joint by 70 years of age [7]. Most women in their sixties have evidence of osteoarthritis affecting

Prevalence and incidence of osteoarthritis

Osteoarthritis affects certain joints while sparing others. For example, in the hands, the distal interphalangeal, proximal interphalangeal, and carpometacarpal joints are all frequently affected, whereas the wrists are rarely affected. Other frequently affected joints include the cervical and lumbosacral spine, hip, knee, and metatarsophalangeal joint. The ankles and elbows are usually spared (although the latter joint has been a focus of pathologic investigations). Two theories have been

The pathophysiology of osteoarthritis

The joints are used over and over again. Whether this use constitutes a dynamic trophic and healthy effect on joints or an injurious effect depends on the activities involved and the vulnerability of the underlying joint. Most daily activities, even if performed repeatedly over many years, do not produce sufficient injury to a joint to cause osteoarthritis, at least not if the joint is healthy. Joint vulnerability is a key concept in understanding when a joint is susceptible and when it is not.

Systemic risk factors

Osteoarthritis is a disease of aging, but age alone does not cause osteoarthritis; rather, the vulnerabilities of the joint that occur as part of aging make the joint susceptible to disease. Specific pathophysiologic accompaniments of aging include an increased response time while anticipating an incoming load such as weight bearing and the loss of strength.

A large proportion of osteoarthritis occurs owing to inheritance. Heritability is the proportion of osteoarthritis occurrence that is

Local joint vulnerabilities

Factors that affect joint shape are likely to have an important role in causing osteoarthritis, especially in the hip. Developmental abnormalities occurring during infancy or childhood that leave a hip joint misshapen and that increase local stresses to cartilage in that hip joint predispose to hip osteoarthritis in early adulthood. The three types of congenital and developmental abnormalities that are most commonly implicated are congenital dysplasia (more common in girls), Legg-Perthes

Obesity

Persons who are overweight have a higher prevalence of knee osteoarthritis than persons who are not overweight, and being overweight precedes the development of knee osteoarthritis. Weight probably increases the risk for knee osteoarthritis by increasing the amount of mechanical load across a joint. Indeed, every pound of weight is multiplied threefold to sixfold in terms of its effect on knee loading. The relationship of obesity to knee osteoarthritis is stronger in women than in men. Although

Factors associated with symptoms in persons with osteoarthritis

As noted earlier, there is considerable discordance between the presence of radiographic osteoarthritis and symptoms in the affected joint. One important reason is that radiographs do not image well structures that are innervated by pain fibers. These structures include the synovium, the joint capsule, the periphery of the meniscus, ligament insertion sites, and periosteal bone [36]. Recent studies of persons with radiographic knee osteoarthritis have compared those with and without symptoms

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    This article was supported by NIH grant AR47785.

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