New York, Dec 2 : Stronger quadriceps muscles, relative to the hamstrings, may lower the risk of total knee replacement, according to a study led by an Indian-origin researcher. Researchers from the University of California, San Francisco (UCSF) said the findings could inform strength-training programmes for people with advanced arthritis in the knee. Advanced knee osteoarthritis is a major cause of pain and disability worldwide. While stronger muscle groups are generally understood to be associated with a lower rate of total knee replacement, their relative importance is not well established. Of particular interest is the relationship between the extensors and the hamstrings, the two most important muscle groups in the knee. The extensors, the muscles on the front of the thigh commonly referred to as the quadriceps, are the strongest muscle group in the body and have essential influence on gait, other activities and biomechanics. The muscles around the back of the thigh known as the hamstrings are responsible for extension of the hip and flexion of the knee, making them equally essential for physical activity. 'The two muscle groups act as counter forces, and the balance between them enables a wide range of activities while protecting the knee joint,' said study lead author Upasana Upadhyay Bharadwaj, from the UCSF. 'An imbalance, in addition to other factors, leads to a change in the biomechanics resulting in the progression of osteoarthritis.' The team evaluated thigh muscle volume in 134 participants and compared 67 patients who underwent total knee replacement of a single knee with 67 control participants who had not undergone knee replacement. The cases and controls were matched for variables including age and gender. The researchers obtained a 3T MRI of the thigh at the time of surgery. They also evaluated MRI findings from two years and four years before the surgery. 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. Comparing patients who had total knee replacement with the control group, a higher ratio of quadriceps to hamstring volume was significantly associated with lower odds of total knee replacement. Higher volumes of hamstrings and gracilis, a long, thin muscle on the inside of the thigh, were also linked with lower odds of total knee replacement. 'Our study shows that in addition to strong muscles individually, larger extensor muscle groups -- relative to hamstring muscle groups -- are significantly associated with lower odds of total knee replacement surgery in two to four years,' Dr. Bharadwaj said. The study findings have implications for both the interpretation of imaging exams and clinical management. The results suggest that training programmes that strengthen the quadriceps in relation to the hamstrings may be beneficial. Although the study focused on people with arthritis, 'even the general public can benefit from our results to preventively incorporate appropriate strengthening exercises,' Dr. Bharadwaj said. The findings were presented at the recent annual meeting of the Radiological Society of North America (RSNA). /IANS