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  • Having strong thigh muscles may reduce the need for total knee replacement in people with knee osteoarthritis.
  • In particular, having stronger quadriceps muscles compared to the hamstrings muscles may be beneficial.
  • The quadriceps can be strengthened with specific exercises such as squats and lunges, or with activities like yoga and Tai Chi.

For people with knee osteoarthritis, having stronger quadriceps muscles, in relation to the hamstrings, could reduce the need for total knee replacement, preliminary research suggests.

The findings could lead to improvements in strength-training programs for people with this degenerative joint disease, and may even benefit others, researchers say.

“While these results are essential for targeted therapy in a population at risk for osteoarthritis, even the general public can benefit from our results to preventively incorporate appropriate strengthening exercises,” study author Dr. Upasana Upadhyay Bharadwaj, from the University of California, San Francisco, said in a news release.

The study was presented Nov. 27 at the annual meeting of the Radiological Society of North America (RSNA). It has not yet been published in a peer-reviewed journal.

An estimated 14 million Americans — including more than 3 million racial/ethnic minorities — have knee osteoarthritis severe enough that it causes symptoms such as pain, stiffness and swelling, according to a large national U.S. health survey.

While older age is a risk factor for this condition, the survey found that more half of people with symptomatic knee osteoarthritis were under 65 years old.

Treatment for knee osteoarthritis generally begins with conservative methods such as physical therapy, weight loss, knee bracing or anti-inflammatory medicines.

If these fail to improve symptoms, a person may need surgery. One type is a total knee replacement, also known as total knee arthroplasty.

Exercise programs, when implemented early after a diagnosis with knee osteoarthritis — and maybe even before then — can improve pain symptoms and functioning in people with this condition.

While many types of aerobic and strength-training exercises can be beneficial, earlier research has found that exercises that focus on strengthening the quadriceps may be especially helpful at reducing pain symptoms.

The quadriceps are a group of four muscles located on the front of the thigh. They are one of the strongest muscle group in the body, and help you stand, walk and run. When you extend (straighten) the leg at the knee, or flex your thigh at the hip (such as when you step up), that’s the quadriceps working.

Around the back of the thigh are the hamstrings, which are involved in movements such as walking, running and jumping. These three muscles are responsible for flexing (bending) the leg at the knee, and extending the thigh at the hip.

These two muscle groups act as counter forces and protect the knee joint during a wide range of activities, said Upadhyay Bharadwaj in the release. However, “an imbalance, in addition to other factors, leads to a change in the biomechanics resulting in the progression of osteoarthritis,” she said.

In the new study, Upadhyay Bharadwaj and her colleagues evaluated thigh muscle volume in 134 participants with knee osteoarthritis who were participating in a U.S. study sponsored by the National Institutes of Health.

Half of participants had undergone a total knee replacement, while the other half (known as the control group) had not. The knee replacement group and controls were matched for factors such as age and gender.

Researchers examined MRI images of participants’ thigh muscles taken at the time of surgery, and two years and four years before the surgery. They used a deep learning computer model to calculate the volumes of the thigh muscles.

People with a higher ratio of quadriceps volume to hamstrings volume were less likely to have had a total knee replacement.

In addition, people with higher volumes of hamstrings and gracilis, a long muscle on the inside of the thigh, were also less likely to have had a total knee replacement.

“Our study shows that in addition to strong muscles individually, larger extensor muscle groups [such as the quadriceps] — relative to hamstring muscle groups — are significantly associated with lower odds of total knee replacement surgery in two to four years,” Upadhyay Bharadwaj said in the release.

While the overall muscle volume in the thigh is important, she said the balance between the extensor and hamstring muscles may be more important for reducing the risk of total knee replacement.

Dr. Sean Rockett, an orthopedic surgeon with Orthopedics New England in Boston, said the results of the new study make sense, because the quadriceps play an essential role in taking pressure off the knee joint.

In people with knee osteoarthritis, “stronger quadriceps would help the patella [kneecap] function better, and potentially produce less pain, thus decreasing the need for total knee replacement,” he said.

Dr. Meredith Warner, an orthopedic surgeon with a private practice in Baton Rouge, Louisiana, agrees that a higher quadriceps volume, compared to the hamstrings volume, is important.

“If you are weak in the [quadriceps], you lack the natural shock absorption [provided by] that muscle group,” she said. In addition, part of the quadriceps crosses both the hip and knee joints, which Warner said is important for distributing stresses in the upper leg.

The quadriceps is also closely related to the iliotibial (IT) band, which runs along the outside of the thigh and stabilizes the hip and knee during walking and running.

“If one has a reduced ratio of [quadriceps] size to hamstrings, the implication is that they are sitting most of the day and quite inactive,” said Warner. “This group of people — sedentary — is well-known to be at higher risk of total knee replacement compared to an active population.”

Kim Bennell, PhD, a research physiotherapist and professor of physiotherapy at the University of Melbourne in Australia, cautions that the new study only looked at the relationship between muscle volume and need for total knee replacement.

“[The study] does not directly evaluate whether prescribing strengthening exercises designed to improve the quadriceps/hamstrings strength ratio leads to a reduced need for joint replacement,” she said.

But the results add to the evidence that strengthening the quadriceps may reduce symptoms of knee osteoarthritis and reduce the need for total knee replacement surgery, she said.

Many types of exercise can strengthen the quadriceps, including squats, lunges and step-ups. Even certain types of yoga may be beneficial for this muscle group.

In a study published last year in the Annals of Internal Medicine, Bennell and her colleagues found that an unsupervised online yoga program reduced pain symptoms and improved functioning in people with knee osteoarthritis.

They didn’t look specifically at muscle strength or whether people needed total knee replacement later on.

”However, research has shown that resistance exercise programs, as well as other forms of exercise such as Tai Chi and yoga, can improve quadriceps strength,” said Bennell, “and so are recommended for people with knee osteoarthritis.”

In a preliminary study, researchers found that stronger thigh muscles reduced the need for total knee replacement in people with knee osteoarthritis. This degenerative joint condition affects millions of Americans, including those under age 65.

In particular, a higher volume of quadriceps muscles versus hamstrings was associated with a lower risk of surgery. A higher volume of hamstrings and gracilis were also linked to a reduced need for surgery.

The quadriceps can be strengthened with specific exercises, such as squats, lunges and step-ups. Activities such as yoga and Tai Chi can also strengthen this muscle group and reduce symptoms of knee osteoarthritis.