| One-Minute Clinician

Knee OA: Older Adults and Osteoarthritis

The population is aging, and osteoarthritis (OA) tends to affect older adults more, so understandably its rates are going up. The increase in obesity is another reason for the increase in rates of OA: it’s becoming a major public health issue. There’s a lot of research to understand the pathophysiology of the disease itself: what’s going on in the knee that’s driving changes in the joints and so on. What other factors are contributing to pain and disability in this condition? We look at how the way the brain processes pain may be changing in people with knee OA. Historically, knee OA has been considered a peripheral regional pain condition whose pain and disability are driven largely by the changes going on in the knee joint, which causes stress on the knee joint and some inflammation, and turns on pain fibers in the knee, and produces pain. All of that is important, and there certainly are peripheral factors that influence knee OA. We also focus on central nervous system factors that happen once the pain signal reaches it, either the spinal cord or the brain or both, and what changes happen in knee OA. There is increasing evidence that at least a fair proportion of people with knee OA seem to display central sensitization—that is, their central nervous system has gotten much better at experiencing pain and they respond more robustly to pain input that can be due to changes in the spinal cord but also changes in the brain. There is now evidence that certain areas of the brain shrink in people with knee OA, so there is some brain atrophy which is attributed to the chronic pain of knee OA, and that when you successfully treat the knee pain, the brain grows back to its normal size to some degree. We are trying to understand more about the way the central nervous system processes pain and how we can address those factors in treatment. OA is not necessarily inevitable, but it’s very common. If we live long enough, many of us are at risk for experiencing OA. But you can reduce your risk by maintaining a healthy body weight and active lifestyle. A trauma is another risk factor. Injuries people may have had even in their earlier years—sport injuries for example—put people at risk for development of OA later in life. There are likely some genetic risk factors for developing OA. There is evidence that African Americans and other minority groups are at risk for higher levels of pain and disability when they develop knee OA. It’s not necessarily that rates of knee OA are higher in the ethnic group. It’s that when knee OA is present, African Americans, which is the group that we’ve studied, experience higher levels of pain. They experience more disability and functional decline. We’re trying to understand the factors that contribute to those ethnic differences in pain.