With the Vermont City Marathon approaching, it makes sense to consider what the long-term effects of recreational running might be on joint health.
Clearly activities like distance running provide substantial health benefits by improving cardiovascular health and even elevating mood and a sense of well-being. Runners also tend to have increased bone density compared to less active people, which could decrease the risk for breaking bones. But is there a price to be paid later in life with a higher risk for hip or knee joint replacement? It makes sense that our car tires wear out after enough miles; don’t our knees and hips behave the same?
Unlike tires, our joints have cartilage surfaces which provide an extremely low friction environment for gliding. With the aid of natural joint lubricants these surfaces are much more slippery than ice sliding on ice. What is truly amazing is that, for many people, only a few millimeters of cartilage can remain relatively intact for a lifetime of millions of steps per year. Surprisingly, unlike many tissues in the body, cartilage has very little if any ability to heal. Once cartilage is lost there is currently no way to get it back like it was. In osteoarthritis the smooth cartilage covering the joint surfaces is lost leaving painful exposed bone ends. Multiple factors contribute to this process. A hip or knee joint that has abnormal geometry or is misaligned significantly could wear out early — like a misaligned car tire. Trauma can overload and destroy cartilage or cause joint instability by disrupting ligaments leading to arthritis.
Obesity also increases the risk for joint degeneration probably both by increasing the already large forces that cartilage needs to endure but also because fat tissue itself can secrete substances systemically in the body that may hurt cartilage.
While there are a couple of studies which indicate that distance running could be a risk for hip and knee arthritis, many more and better done studies do not demonstrate any increased risk for the avid runner. In fact, it may be somewhat protective compared to a sedentary lifestyle. Gradual training provides greater strength and muscle control to better manage joint impact forces. Cartilage and the bone adjacent to it probably adapt to some degree as there is some evidence from MRI studies that cartilage thickness can actually increase with more activity. In a group of regular long distance runners compared to a group of non-runners, no differences in knee x-ray changes occurred over a period of 18 years. Additionally a group of runners who had knee cartilage measurements on MRI and then repeat MRI measurements 10 years later did not show any change in the cartilage for almost all of the runners.
Overall, most runners should not worry about wearing out their joints. Of course, there are ways to cause harm even with a good activity by running to the point of injury or continuing to pound the pavement when injured. In general, we would all be in better shape and have healthier joints taking a lesson from the marathoners. One of these years I hope to join the race. Good luck and enjoy your run!
Nathaniel Nelms, MD, is an orthopedic physician at the UVM Medical Center and assistant professor with the Larner College of Medicine at UVM. Dr. Nelms specializes in primary and revision hip and knee joint replacement. Learn more about Orthopedic Care at the UVM Medical Center.