An Overview of Osteoarthritis By Carol Eustice - Reviewed by a board-certified physician. Updated August 18, 2016 Osteoarthritis, one of more than 100 types of arthritis and related conditions, is the most prevalent type of arthritis. In the United States, about 27 million people live with the condition. Osteoarthritis is most common among adults over 65 years old, but people of any age can develop it.Prevalence rises significantly after age 50 in men and after age 40 in women. According to the American College of Rheumatology, 70 percent of people over the age of 70 have x-ray evidence of osteoarthritis. "Wear-and-Tear"Osteoarthritis is commonly referred to as the wear-and-tear type of arthritis. Other names include degenerative joint disease, degenerative arthritis, DJD, and osteoarthrosis.Osteoarthritis has long been explained as the result of the breakdown of cartilage in one or more joints. Cartilage is composed of 65 to 80 percent water, collagen (fibrous proteins), proteoglycans (proteins and sugars which interweave with collagen), and chondrocytes (cells that produce cartilage). Article Can You Have Osteoarthritis and Rheumatoid Arthritis Together? Article Treatment Recommendations for Hand Osteoarthritis Cartilage is a hard but slippery tissue which serves as a cushion between the bones of joints, allowing the bones to glide over one another. It also absorbs shock from physical movements.When cartilage loss occurs, joints can deteriorate to the point of rubbing bone against bone. Changes in structures that surround joints (muscles and tendons), fluid accumulation, and bony overgrowth (osteophytes or bone spurs) can develop, leading to severe chronic pain, loss of mobility, and disability.Osteoarthritis can affect joints in the hands and fingers, hips, knees, feet, and spine. Based on x-ray evidence, the distal and proximal interphalangeal joints of the hand are most commonly affected by osteoarthritis, though they may not be associated with typical symptoms. The hips and knees are the next most common sites of osteoarthritis and are almost always symptomatic. The first metatarsal phalangeal and carpometacarpal joints also are common sites of osteoarthritis observed on x-ray. The shoulder, elbow, wrist, and metacarpophalangeal joints are rare sites of osteoarthritis unless related to injury, trauma, or occupation.Other FactorsWhile the aforementioned explanation of wear and tear (cartilage degeneration) is not inaccurate, it is incomplete. In fact, there is more to it than that. It is not simply mechanical. Many other factors play a role in the development of osteoarthritis including biologic factors, proinflammatory mediators, and proteases. These factors may be genetic, metabolic, environmental, or traumatic. While the destruction of joint cartilage is the most well-known characteristic of osteoarthritis, we must understand that wear and tear from joint loading stimulates the production of proinflammatory factors and proteases which contribute to joint deterioration. Article What is Subchondral Bone? Article 10 Things You Didn't Know About Osteoarthritis In a joint affected by osteoarthritis, all joint tissues are affected, not just the cartilage.Development and Progression It can be difficult to determine when osteoarthritis onset occurs and which joint tissues are affected early on unless there is a traumatic event which causes an injury and that can be pinpointed, such as a torn ligament.While MRI studies can detect early structural changes consistent with osteoarthritis, plain x-rays are routinely ordered, at least initially. But, by the time there is x-ray evidence of osteoarthritis, the disease can be quite advanced. X-rays reveal cartilage loss, joint space narrowing, subchondral sclerosis, subchondral cysts, and osteophytes. MRI images can reveal subtle changes to cartilage, synovitis, bone marrow lesions, and degenerative changes within soft tissues. As osteoarthritis progresses, the entire joint may become involved, causing the component parts to fail. Despite knowing that, the prognosis for someone with osteoarthritis is difficult to predict. Not everyone with the condition progresses at the same rate, responds to a particular treatment modality the same way, or develops severe symptoms if in early or mild stages.Risk FactorsFactors that increase the risk of developing osteoarthritis include: Aging—It is known that the incidence and prevalence of osteoarthritis increases with age. It is also thought that aging makes joints more susceptible to developing osteoarthritis—there is cellular aging as well as extracellular changes (thinning of cartilage with age). By 2030, approximately 20 percent of Americans will be over 65 years old and at high risk for developing osteoarthritis. Female gender—Hand and knee osteoarthritis is more prevalent in women than men. The prevalence of hip osteoarthritis is essentially equal in men and women. Injury to joints—After joint injury occurs, post-traumatic osteoarthritis can develop. The changes are typically observed within 10 years of injury. Osteoarthritis can develop, after injury, to soft tissues, such as a ligament tear, because proinflammatory mediators rush to the injury site and may initiate the development of osteoarthritis. There also may be injuries that directly involve joints, like fractures). Article Can Cracking Your Knuckles Really Cause Arthritis? Article Bariatric Surgery and Total Knee Replacement Occupational activity—With occupations that require intense joint loading, especially repetitively, there is an increased risk of developing osteoarthritis. This is true of jobs that require lifting, kneeling, squatting, or climbing. As would be expected, repetitive motion and added force increases the burden on involved joints. Overweight or obesity—Excess body weight adds burden to weight-bearing joints. Interestingly, being overweight increases the risk of hand osteoarthritis, too. This suggests that there may be metabolic effects associated with overweight and obesity that increase the risk of osteoarthritis. Genetic predisposition—Studies have associated certain gene variations with an increased risk of developing osteoarthritis.A Word From VerywellUnderstanding that osteoarthritis is more than simply a consequence of aging or worn out joints is important. Recognizing that there are factors which increase risk of developing osteoarthritis and that some may be modifiable is also important. We have learned over the years that the disease is more complicated than "worn out cartilage". In fact, structures in and around joints are also affected by osteoarthritis.Researchers are working on developing one or more medications that perform similarly to DMARDs (disease-modifying anti-rheumatic drugs) for inflammatory types of arthritis by slowing disease progression. While the acronym DMOADs for disease-modifying osteoarthritis drugs has already been applied, we are still awaiting the development and marketing of an effective DMOAD. Sources:Osteoarthritis. Handout on Health. NIAMS. April 2015.Osteoarthritis Epidemiology and Risk Factors. The Johns Hopkins Arthritis Center. Updated April 25, 2012.Paul E. Di Cesare et al. Chapter 98. Kelley's Textbook of Rheumatology. Elsevier. Ninth edition.Richard F. Loesner. MD. Pathogenesis of Osteoarthritis. UpToDate. Updated June 21, 2016.