Sometimes called degenerative joint disease or degenerative arthritis, osteoarthritis (OA) is the most common chronic condition of the joints, affecting approximately 27 million Americans. Although it occurs in people of all ages, osteoarthritis is most common in people older than 65.
In osteoarthritis, there is a breakdown in the cartilage covering the ends of bones where they meet to form a joint and allow movement. As the cartilage wears away, the bones become exposed and rub against each other. The deterioration of cartilage also affects the shape and makeup of the joint so that it no longer functions smoothly. You may notice a limp when you walk, or you may have trouble going up and down stairs because those movements put additional stress on the joint.
Other problems can occur inside the joint as cartilage breakdown affects the joint components. Fragments of bone or cartilage may float in joint fluid, causing irritation and pain. Spurs, or osteophytes, can develop on the ends of the bones, damaging surrounding tissues and causing pain. Fluid inside the joint may not have enough of a substance called hyaluronan, which may affect the joint’s ability to absorb shock. And although inflammation is not a main symptom of osteoarthritis, it can occur in the joint lining in response to the cartilage breakdown.
What Are the Symptoms of Osteoarthritis?
Symptoms of osteoarthritis vary, depending on which joints are affected and how severely they are affected. However, the most common symptoms are stiffness, particularly first thing in the morning or after resting, and pain. The most commonly affected joints are the lower back, hips, knees and feet. When those joints are affected you may have difficulty with such activities as walking, climbing stairs and lifting objects.
Other commonly affected joints are the neck and fingers, including the thumb base. When finger and hand joints are affected, osteoarthritis can make it difficult to grasp and hold objects, such as a pencil, or to do delicate tasks, such as needlework.
What Causes Osteoarthritis?
Like other chronic conditions, osteoarthritis has no single, specific cause. Instead, there are several factors involved in the disease, including heredity and lifestyle. While osteoarthritis was long believed to be a simple mechanical process in which joints wore out, researchers now view it as a disease of the joint. The following factors may contribute to osteoarthritis:
Genes: One possibility is that certain people may have a defect in the gene responsible for the body’s production of collagen, the protein that makes up cartilage. This somewhat rare genetic defect might lead to abnormally weak cartilage that wears down after just a few decades of normal activity, causing osteoarthritis as early as age 20.
Other genetically based traits may result in slight defects in the way the bones and joints fit together so that cartilage wears away faster than usual. The inherited trait known as joint laxity, or double-jointedness, in which the joints bend farther than the usual angles, may also increase the risk for osteoarthritis. Simply inheriting a gene that makes you more susceptible to osteoarthritis doesn’t mean you will get the disease, however. Your lifestyle – that is, the way you eat, exercise, sleep and whether you have bad habits such as smoking – has a tremendous impact on whether you will develop OA.
Weight: Your hips and knees bear the brunt of your body’s weight. Being overweight puts additional pressure on these joints. For every pound you gain, your knees gain three pounds of added stress; for your hips, each additional pound translates into six times the pressure on these joints. Many years of carrying extra pounds can cause the cartilage that cushions your joints tends to break down. Obesity may lead to osteoarthritis on its own, or it may combine with other factors such as genetic susceptibility to produce the disease and worsen its symptoms.
Some research has shown a link between being overweight and having an increased risk of osteoarthritis in the hands, but the reason for that connection is unclear. One theory is that excess fat tissue itself produces inflammatory chemicals that travel throughout the body and are capable of causing damage in places other than weight-bearing joints.
Injury and overuse: Sometimes repetitive movements or serious injuries to joints (such as a fracture or surgery) can lead to osteoarthritis down the road. Some full-time athletes, for example, repeatedly damage certain joints, tendons and ligaments, which speeds cartilage breakdown. Even joints such as shoulders (which don’t bear much weight and are unlikely to have osteoarthritis) can develop the disease after injuries or repeated stressful activities.
The constant knee bending required by some types of work, such as landscaping, can make cartilage wear away more quickly than moderate use of those joints.
Others: Several other factors may contribute to osteoarthritis. These factors include other bone and joint disorders like rheumatoid arthritis and certain metabolic disorders such as hemochromatosis, which causes the body to absorb too much iron, or acromegaly, which causes the body to make too much growth hormone.