Research has long established that among the greatest risk factors for development and progression of knee osteoarthritis, or degenerative joint disease, are being overweight or obese. Higher body mass index (BMI) places heavier loads on joints in the lower limbs, including the knees, each time someone stands up or walks.
“These greater loads and adverse biomechanics are thought to play an important role in osteoarthritis,” says Adam Culvenor, of Paracelsus Medical University in Salzburg, Austria. “However, overweight people are also at risk of hand and spinal osteoarthritis, and clearly we aren’t walking around on our hands and spines.”
Researchers are learning that adipose, or fatty, tissue isn’t merely passive, but it is an active organ that can release chemicals that lead to inflammation. “The combined detrimental effects of biomechanics and biochemistry associated with a greater BMI play an important role in knee osteoarthritis,” Dr. Culvenor says.
Dr. Culvenor and colleagues recently published “Thigh muscle specific strength and the risk of incident knee osteoarthritis” in Arthritis Care & Research, which zeroes in on thigh muscles in particular. By measuring strength of those muscles — which includes both muscle’s capacity to produce force as well as its structure — they discovered that muscle strength can increase knee osteoarthritis risk development in women, although it had no effect on men.
The relationship was confounded by body mass index (BMI) — a very strong risk factor for osteoarthritis. “The different results between men and women in our study could be explained by the muscles response to greater BMI,” Dr. Culvenor says. “In men, a greater BMI was associated with increased muscle strength, whereas in women a greater BMI wasn’t associated with increased strength.”
It is particularly important for female patients to maintain healthy body weight by eating well and staying active, according to Dr. Culvenor. “But just as importantly, the protective value of having strong thigh muscles should also be emphasised,” he says. “We know that doing strengthening exercises makes you stronger.”
Of course, having strong thigh muscles won’t necessarily protect women from developing knee osteoarthritis, because many other factors play a role in the development of the diseases. “Our results suggest that making thigh muscle strengthening exercises a part of a weekly routine may help to lower the risk of incident knee osteoarthritis,” Dr. Culvenor says.
Physical therapists can help patients target deficits in muscle strength, including through muscle biofeedback and neuromuscular stimulation, he says. And although muscle strengthening programs haven’t been demonstrated to prevent osteoarthritis development or progression, there is strong evidence that they can improve pain and daily function, reduce symptoms, and optimize quality of life.
“In the end, patients rarely seek medical attention for a sign on a knee X-ray. They seek solutions for pain, disability, and impaired quality of life,” Dr. Culvenor says. “Muscle strengthening and neuromuscular training are an important part to this solution.”
It’s not entirely clear why women are impacted by muscle strength so much more than men are, according to Dr. Culvenor. It might be that women overall are not as strong as men, so muscle weakness can impact them more severely.
“But there are lots of other sex-specific factors that are likely to contribute to this relationship including hormonal differences, biomechanical differences — women have wider hips, laxer joints, and different biomechanics than men,” he says. “That’s what makes research into this area to exciting and rewarding.”
The findings have motivated him and his colleagues to learn more about the role that fatty tissue plays in knee osteoarthritis development and progression.
“It is becoming apparent that being overweight does not just put more force through the knees, but it can also act biochemically on the joint and lead to osteoarthritis,” he says.