|The News on Knees|
Does running cause knee arthritis?
OA is relatively common, with ten per cent of people over fifty-five years old reporting painful osteoarthritis in their knees. People engaged in sports or other physically demanding activities are known to be at an increased risk of osteoarthritis in the joints they use most. Part of this apparent correlation can be explained by increased risk of joint injury. It seems logical that overuse of a joint may lead to osteoarthritis, but does the research support this apparently straightforward premise?
Animal studies reveal a pattern of increased OA incidence in joints where there is a history of joint injury or excessive exercise. What about humans, though? In a one-mile run, we take at least 1,000 to 1,500 strides. That's a lot of "overuse" on the knees. Does research support the same with humans as it does for animals? Well, let's first look at what OA is.
Most joints in the body have a layer of cartilage that covers the ends of the bones. This cartilage helps spread out the compressive and shear forces that are applied to the joint, such as when we put weight through the joint (i.e., running). Without this cartilage, we would have bone on bone contact-this would be painful. When OA occurs, the cartilage is starting to break down. We get little cracks and divots in the cartilage. So the cartilage can't distribute that force as much and we get more pressure coming through to the bone where all the nerves are. According to Sue Hunter, joint transplantation program coordinator, McCaig Institute for Bone and Joint Health in Calgary, "The surface of each bone in your knee joint is covered with smooth, shiny tissue called articular cartilage that cushions and protects while allowing near frictionless movement. Because cartilage has no nerve endings or blood supply, once it has been damaged it will not heal on its own. Typically you begin to feel pain when the underlying bone becomes exposed." This is why OA hurts.
So how does it occur?
Here's the anatomy lesson. Think of the knee joint as a living active structure in which there is an ongoing balance between joint degeneration (wear and tear/injury) and subsequent repair processes (band-aides). With the process of developing OA, the ‘repair process' team gets beat out by the ‘wear and tear' team. There's an imbalance of joint restoration. In the end and simply put, OA may be considered "joint failure." Development of OA initially occurs in joints that are susceptible to or have undergone trauma. There are chemical changes that happen in the joint that affect the cartilage and synovial lining (the structure that secretes a friction-fighting lubricant). These changes are driven by altered mechanical stress such as the bones of the knee not lining up well, too much of the wrong movements occurring, injury, and your bone/cartilage health genes (yes, your mother's and father's genes can come back to haunt you). The force-distributing capability of the knee is reduced and may continue to get worse over time.
So how can we reduce the risk of developing OA? Study after study report that the single best intervention is exercise. Muscles around the knee joint help to absorb some of the impact force and stabilize the knee to maintain proper alignment of the joint surfaces. Exercise that helps to build the strength and endurance of these muscles also improves their ability to protect the joint.
Dr. Katherine Boyer, research associate in mechanical engineering at Stanford University states, "There is a general misconception that running is bad for the knees. Recent longitudinal studies have shown that there is not a higher incidence of osteoarthritis (OA) among seasoned runners compared to non-runners. In general, for healthy joints (i.e., no history of traumatic injuries), cartilage becomes thicker when exposed to higher levels of joint loading. The good news for runners is that the risk of OA is much higher in the non-active and obese population than it is in the healthy active populations." So, keep the weight off, folks.
Running technique is also likely to play a role. Runners who have a bouncy stride, where they move up and down quite a bit with each step, are going to land with more force on the knee. Also, those runners who land with their foot well ahead of their bodies force the leg to act like a break, which also increases the force on the knee joint. The third factor is running beyond the ability of the knee muscles to function properly, such as running to exhaustion, or dramatic increases in training volume may increase the risk of injury. In addition, there is a growing stack of evidence about the importance of stability and balance on the risk and severity of OA. Many researchers feel that balance and stability training should be an integral part of a training program to reduce the risk of OA.
Well-known Calgary runner and researcher Dr. Ken Myers states, "My feeling is that running may have the potential to cause joint damage if individuals don't take a sensible approach to training. However, I believe that a training program involving considered increases in volume and intensity and incorporating a variety of surfaces (i.e., grass and trails as well as concrete) will ultimately lead to significant improvements in joint health."
The last risk factor is previous knee injury. If you've had damage to the ligaments of the knee, tissue that helps hold the bones together, cartilage (meniscus) injury, or previous surgery, the risk of OA is much higher. In these cases, you should consult with your health-care provider before undertaking a running program.
The benefits of running easily outdistance the disadvantages. Normal wear does not actually cause tear. Recreational running does not cause OA. However, there is a large body of evidence that supports the notion that if you succumb to a knee joint injury, you are more likely to develop OA in that joint, and if you overuse that joint (intense, repetitive compressive/shearing activity) your risk of joint disease is increased.
About the Authors
Kris Head is a practicing physiotherapist and clinic director of two physiotherapy clinics: LifeMark Physiotherapy Village Square and Chestermere. He is a regular runner and teaches courses in injury assessment and treatment.