A step-by-step study of arthritis risk

Whether you’re walking across your living room, taking a leisurely stroll in the park or running a marathon, every step you take hammers your knee with some degree of force from your body weight. Over the course of a lifetime, this repeated stress almost inevitably leads to damage—often in the form of osteoarthritis, a degenerative joint disease that causes pain and stiffness.

“We expect to see denser bones and thinner cartilage as a person ages, and both those conditions are markers for osteoarthritis,” David Hudson says. “There’s no doubt that osteoarthritis is related to age. It’s a wear-and-tear condition.”

Hudson, CHS ’99M, ’04PhD, assistant professor of health, nutrition and exercise sciences, is using new tools to track the development of osteoarthritis. A physical therapist for 13 years before returning to UD to earn graduate degrees in biomechanics and movement science, Hudson says he hopes to find ways to detect early signs of the disease. By doing so, he says, it will be possible to devise better methods of preventing or delaying its progression or minimizing its effects.

Getting older and being overweight already have been identified as risk factors for osteoarthritis, but Hudson says he hopes his research can identify additional ones.

“The more risk factors we can identify for developing osteoarthritis, the more we can do to mitigate it,” he says. “Tracking whether the bones are getting denser and/or the amount of cartilage is decreasing can be a gauge of knee health. I’m researching whether those changes can show if you’ve already developed osteoarthritis or if you’re heading that way.”

Hudson’s research focuses on the shape of the bones above and below the knee, as well as the “twist” that occurs within those bones during walking or other movements. “There’s a big variation in bone shape, even within a group of healthy people,” he says, citing such common conditions as so-called “bowlegs” and “knock-knees.”

He also studies the cartilage around the knee, using magnetic resonance imaging (MRI) to assess any thinning or deterioration. Although most researchers and clinicians use X-rays to estimate cartilage loss, Hudson says MRIs are a more accurate tool.

In explaining how cartilage diminishes over time, he compares it to the thickly cushioned insole of a new pair of sneakers. As a person wears those sneakers day in and day out, the pounding of his or her feet slowly begins to flatten out the air pockets of the cushion, making the insole stiffer and less able to absorb the shock of walking. Eventually, the insole becomes thin and stiff and begins to crack. In the same way, Hudson says, cartilage around the knee breaks down from years of absorbing stress. As it breaks down, the tibia, the major bone in the lower leg, bears more of the brunt of the stress. Hudson is investigating whether the top of that bone, just below the kneecap, begins to thicken in response and also becomes less able to absorb the shock. If so, that thickening would cause the cartilage to break down even faster as the stress on it increases.

“We don’t know which is affected first, the bone or the cartilage, but we know it’s a vicious cycle,” Hudson says. “If you get osteoarthritis in your knees or your hips, it can really immobilize you. It can be devastating.”

The disease is increasingly the subject of research, at UD and elsewhere, especially because, as the Baby Boom generation ages, the incidence of osteoarthritis is expected to grow. To study cartilage breakdown, researchers traditionally have used X-rays of the knees. Because X-rays don’t show the cartilage itself, those studying the disease have measured the area between the top of the tibia and the bottom of the kneecap and assumed that space was filled with cartilage.

Now, using MRIs, the actual cartilage can be seen on the images, allowing for more precise measurements of deterioration, Hudson says. MRIs also have the advantage over X-rays of not exposing research subjects to radiation. They have been too expensive to use in previous research, but as the cost has come down, they have become a more practical tool, Hudson says.

He says he became interested in studying bone shape and a person’s gait in relation to osteoarthritis by observing his physical therapy patients who had the disease, as well as his own grandmother’s condition.

“I noticed in those patients and in my grandmother that their leg structure seemed to change as their osteoarthritis progressed,” he says.

Hudson’s current work involves a pilot study of women, who develop osteoarthritis more frequently than men. The 15-20 women in the study represent a range of ages from their 20s to their 70s. He plans to assess the shape and density of their bones, the amount of knee cartilage and the force that’s put on their joints as a result of their gait. By studying those factors over time, he says, he hopes to gather sufficient data about osteoarthritis markers to move on to a large-scale study.

“Eventually, I think, my research will take me back to children, how their skeletons develop and how they walk,” Hudson says. “If a certain type of bone structure or gait is a true risk factor, then maybe the chance of developing osteoarthritis can be addressed at a very early age. But, that’s research for the very long term.”

—Ann Manser, AS ’73, CHEP ’73