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.