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CHICAGO -- Larger quadriceps relative to hamstrings may lower the risk of needing total knee replacement surgery, according to findings from the NIH's Osteoarthritis Initiative.

In fact, an evaluation of thigh muscle volume in 134 individuals with osteoarthritis showed that those with a higher quadricep-hamstring ratio had an 82% lower odds of undergoing total knee replacement (OR 0.18, 95% CI 0.04-0.58, P=0.005), reported Upasana Bharadwaj, MD, of the University of California San Francisco.

"Strengthening exercises that target quadriceps relative to hamstrings may potentially delay the risk of eventual total knee replacement," she said here during an oral presentation at the annual meeting of the Radiological Society of North America.

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

The findings may have implications for both the interpretation of imaging exams and clinical management, according to the researchers.

More than half of people diagnosed with knee osteoarthritis are projected to need total knee replacement surgery eventually, and while Bharadwaj said the findings "are essential for targeted therapy in a population at risk for osteoarthritis, even the general public can benefit from our results to preventatively incorporate appropriate strengthening exercises."

Other results from the analysis showed that greater hamstring and gracilis muscle volumes were also significantly linked with lower odds of total knee replacement surgery:

• Hamstring: OR 0.93 (95% CI 0.89-0.97, P=0.002)
• Gracilis: OR 0.92 (95% CI 0.87-0.96, P=0.01)

"Although we presume that overall muscle volume is important as a surrogate marker for muscle strength, the ratio, hence the balance, between extensor and hamstring muscles may be more important," Bharadwaj said.

Researchers observed no significant associations between need for total knee replacement and either absolute muscle volumes or volumes of the adductors or sartorius muscles, or subcutaneous fat.

"This study suggests that if you redress the biomedical balance in the front of the knee you may be able to protect yourself against needing total knee replacement down the road," said session moderator Justin Lee, MBBS, a sports medicine specialist at Fortius Clinic in London.

Lee, who was not involved in the research, said that exercises that promote leg extension can help strengthen quadriceps muscles.

In conducting their study, Bharadwaj and colleagues obtained MRI scans of thigh muscle volume from 134 participants in the (average age 62 years, 52% women, body mass index [BMI] 29.9), including 67 patients who underwent total knee replacement surgery on a single knee.

Surgery patients were matched with 67 control participants in the initiative who had not undergone knee replacement using propensity-scoring for age, sex, BMI, Kellgren-Lawrence grades, the Western Ontario and McMaster Universities Osteoarthritis Index , and the Physical Activity Scale for the Elderly .

Researchers performed 3T axial thigh T1-weighted fast spin echo MRI sequences at surgery (or within a year for control participants), and surgery patients needed to have a scan within 2 or 4 years of surgery as well. They used a previously trained deep-learning model to segment and compute volumes of the muscles of the thigh -- measures that are tedious to compute manually. Specifically, the MRI slices compared volumes of the quadriceps, hamstrings, adductors, sartorius, and gracilis muscles, and also the subcutaneous fat.

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