Stronger thigh muscles might help prevent the need for total knee replacement surgery, according to research presented Monday at the Radiological Society of North America’s annual meeting at McCormick Place. 

In the United States 14 million adults have symptomatic knee osteoarthritis, and more than 600,000 patients undergo total knee replacement surgery each year, “causing significant economic burden and a challenging recovery, involving physical therapy and lifestyle adjustments,” according to Dr. Upasana Upadhyay Bharadwaj of the University of California San Francisco, the lead author of the new study.

Researchers said their findings could be used to better inform strength-training programs for those with advanced arthritis in the knee. 

Osteoarthritis is a type of arthritis caused by “age-related wear and tear,” according to the American Academy of Orthopaedic Surgeons. It often occurs in those over 50, but younger people can experience effects as well. 

A 2019 study from Blue Cross Blue Shield found the average price for an inpatient knee replacement was $30,249.

It’s one of the most “chronic degenerative and progressive conditions,” Upadhyay Bharadwaj said.

It is generally accepted that stronger muscle groups tend to lower the risk of total knee replacement surgery, but this study explored the relationship between the quadriceps, the extensor muscles at the front of the thigh, and the hamstring muscles at the back of the thigh. The quadriceps are the strongest muscle group in the body and heavily affect a person’s gait, and the hamstrings are responsible for hip extension and bending of the knee. 

“The two muscle groups act as counter-forces, and the balance between them enables a wide range of activities while protecting the knee joint,” Upadhyay Bharadwaj said. “An imbalance, in addition to other factors, leads to a change in the biomechanics resulting in the progression of osteoarthritis.”

Upadhyay Bharadwaj, who works at the University of California San Francisco, compared the thigh muscle volume of 134 participants from the Osteoarthritis Initiative, a nationwide study sponsored by the National Institutes of Health. All the participants had osteoarthritis, with half having undergone total knee replacement of a single knee and the other half not having surgery on either knee. 

By studying MRI images, Upadhyay Bharadwaj and her colleagues determined that a higher ratio of quadricep muscles — relative to the hamstrings — was “significantly associated with lower odds of total knee replacement surgery in two to four years.” 

This study focused on people with arthritis, but Upadhyay Bharadwaj said everyone could benefit from thigh-strengthening exercises.