Upper Leg Muscle Strength and Osteoarthritis

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The summary below is from the full report titled "Quadriceps Strength and Osteoarthritis Progression in Malaligned and Lax Knees." It is in the 15 April 2003 issue of Annals of Internal Medicine (volume 138, pages 613-619). The authors are L. Sharma, D.D. Dunlop, S. Cahue, J. Song, and K.W. Hayes.

What is the problem and what is known about it so far?

Osteoarthritis is the most common type of arthritis in middle-aged and older people. It often occurs in weight-bearing joints such as the knees and hips. The pain may limit ability to get up from a chair, stand, walk, or climb stairs. The pain tends to get worse with activity, so that pain is worst at the end of the day. Treatment is aimed mainly at relieving symptoms and maintaining function. At present, no treatments change the course of the disease itself. Treatments include simple painkiller drugs, weight loss if needed, physical therapy, and regular exercise. In addition, strengthening the muscles around affected joints may help relieve pain and improve function in the short term. The actual relationship between muscle strength and the course of the disease itself, however, is not clear.

Why did the researchers do this particular study?

To study whether greater strength of the muscle on the front upper portion of the leg (quadriceps muscle) slows down the natural worsening of arthritis in people with osteoarthritis of the knee.

Who was studied?

237 men and women with knee osteoarthritis. Their average age was about 64 years.

How was the study done?

The researchers recruited people with symptoms and x-ray findings of knee osteoarthritis. They tested quadriceps strength of these people using a device that measures muscle force against resistance (isokinetic dynamometer). They took x-rays of both lower extremities to see whether the two bones that meet in the knee joint were in line or crooked in some way (malaligned). They also used special tests to measure the looseness (laxity) of each knee joint. The researchers then followed the participants for 18 months to see whether their knee osteoarthritis stayed the same or worsened. Worsening arthritis was defined as more joint space narrowing on knee x-rays. The researchers compared factors that were measured at baseline (quadriceps strength, knee alignment, knee laxity) among participants who did and did not have worsening joint space narrowing.

What did the researchers find?

Using data from the entire group of participants, the researchers found no significant relationship between quadriceps strength at baseline and worsening x-ray findings. Among people who had malaligned knees, baseline quadriceps strength was associated with greater risk for joint space narrowing. Among people with lax knees, baseline quadriceps strength also was associated with greater risk for joint space narrowing.

What were the limitations of the study?

Quadriceps strength was measured only at baseline. How changes in strength and strengthening exercises affect arthritis progression was not tested.

What are the implications of the study?

Greater quadriceps strength may not protect and could worsen arthritis in some people with osteoarthritis who have malaligned or lax knees. These results do not mean that physical activity or exercise in general is harmful in adults with knee osteoarthritis but suggest that, to maintain strength, special exercise programs should be developed for people with malaligned or lax knees.