When I hobbled into the office of a sports doctor in October, I had already considered some of the reasons my foot might be hurting. I had recently started running again after many years away from the sport, and I figured it could be a strained ligament, an inflamed tendon or plantar fasciitis, which ended my marathon-running habit more than a decade ago. The diagnosis I received was something I had never considered: osteoarthritis. Just a few months shy of 40 at the time, I thought I was too young to have the kind of joint degeneration that, I had always assumed, tended to afflict people much later in life. Disheartened, I discovered I'm not alone. Although osteoarthritis, often called OA, ordinarily shows up after age 65, it's not uncommon for younger people to show signs of wear in their cartilage. This shock-absorbing connective tissue cushions the spaces where bones meet and allows those bones to slide easily as they move. OA may be growing more common, given that medical costs related to the condition have risen. A variety of factors, including obesity, genetics and sports injuries, can explain why some people get the condition early. And even though the diagnosis initially struck me as a sign that I was doomed to a future of progressive deterioration and decline, it turns out there are plenty of ways to manage arthritis when it strikes relatively early in life. Those strategies rarely require replacing joints or quitting favorite activities. "Most of the time when I see people in their 30s and 40s with early-onset arthritis, it is very treatable," says Bashir Ahmed Zikria, a sports medicine orthopedist at the Johns Hopkins School of Medicine in Baltimore. "It's not a death sentence." Arthritis, which generally refers to joint inflammation, comes in many forms, including rheumatoid arthritis, gout and lupus. Overall, 1 in 5 adults in the United States have received an arthritis diagnosis, according to the Centers for Disease Control and Prevention, totaling more than 52 million people. Osteoarthritis is by far the most common form, affecting at least 27 million Americans. The condition most often affects the spine, knees, hips and hands, says Virginia Krauss, a rheumatologist at the Duke University School of Medicine in Durham, N.C. But it can strike any joint in the body. And risks rise with age. About 14 percent of Americans ages 25 and older have been diagnosed with OA, according to the CDC, compared with more than 33 percent of those ages 65 and older. As common as it is, though, diagnosing OA can be tricky. Doctors often need to combine clues from physical exams, medical histories and imaging tests to figure out what's going on. Joint injuries also come into play, particularly among athletes. In studies of injuries to the knee's anterior cruciate ligament, or ACL, as many as 80 percent of patients show signs of osteoarthritis in images within the next five to 15 years. Studies show high rates of arthritis in former football and soccer players. Risks rise dramatically even when athletes hurt their knees as teenagers. And, Krauss adds, the older you are when you injure a joint, the more quickly OA is likely to follow. Past joint injuries weren't a factor for me, and running does not increase risks of developing arthritis, studies show. Instead, my doctor relied on a quick exam to identify a tendon that was causing pain above the arch on my right foot. Then he ordered X-rays, which clearly showed a reduction in cartilage between two bones underlying that tendon. He suspected the tendon was working extra hard to support the weakness there, and the subsequent inflammation was causing me distress. Even in cases like mine, though, images can be deceptive, Krauss says. And she has seen it go both ways: Conditions that look advanced on an X-ray may not cause any discomfort, while severe arthritic pain may not be reflected on images at all. As for dealing with the pain of OA, age can help determine the plan of attack. In late