August 31, 2009
Strong Thigh Muscles Protect Women From Knee Osteoarthritis
Women with the strongest quadriceps appear to be protected against the development of knee osteoarthritis (OA) symptoms, according to a new study. While thigh muscle strength does not predict the presence of knee OA uncovered in x-rays, it does predict incidence of painful or stiff knee OA.
The knee is the weight-bearing joint most commonly affected by osteoarthritis. The Centers for Disease Control and Prevention (CDC) estimate that 26.9 million adults are affected by OA, with 16 percent of those cases occurring in the knee. Approximately 18.7 percent of symptomatic knee OA patients are female and 13.5 percent are male. Total expenditures for treatment of arthritis were estimated at $32 billion in 2005.
Neil Segal, M.D., M.S., and colleagues at the University of Iowa Hospitals and Clinics followed 3,026 men and women ages 50-79 over a 30-month period in the Multicenter Knee Osteoarthritis Study (MOST) to assess whether knee extensor strength would predict OA that can be determined through X-ray or symptomatic knee OA. Of those enrolled, a total of 2,519 knees were included in the study of radiographic knee OA and 3,392 knees were evaluated for the combination of radiographic OA and symptoms of OA that include pain, aching or stiffness on most days of the month.
Participants were evaluated for thigh muscle strength using an isokinetic dynamometer, a device that measures the strength of different muscle groups. The balance of muscle strength between quadriceps and hamstrings (H:Q ratio) was used to assess weakness in the lower extremity musculature. Knees were x-rayed at the onset of the study and at the conclusion to determine the presence of OA. A telephone screen at the beginning and end of the study was conducted to establish if frequent pain, aching or stiffness was present in the knee.
By the conclusion of the study 48 of 680 men and 93 of 937 women developed OA detected by x-ray. At the end of the 30-month period 10.1 percent of women and 7.8 percent of men displayed signs of symptomatic knee OA. "Our results showed thigh muscle strength was not a significant predictor of radiographic knee OA," the authors were quoted as saying. Women in the top third of peak knee extensor strength had a lower incidence of symptomatic knee OA, while men with strong thigh muscles had only a slight advantage over men with weaker knee extensor strength. "The H:Q ratios were not predictive of symptomatic knee OA in either men or women," added the researchers.
Researchers acknowledged the study was limited by not including assessments of hip abductor strength. "Study of hip abductor strength, which is important for control of the knee joint, may be useful in a more comprehensive study of risk for OA of the knee," Dr. Segal is quoted as saying. "These findings suggest that targeted interventions to reduce risk for symptomatic knee OA could be directed toward increasing knee extensor strength."
SOURCE: Arthritis Care & Research, September, 2009