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Strong quad muscles may slow knee osteoarthritis: participants who had the greatest quadriceps strength were 60% less likely to lose knee cartilage.

WASHINGTON -- Strong quadriceps muscles appear to protect against cartilage loss in some parts of the knee in most people, but larger muscle mass in the knee may be associated with x-ray progression of knee osteoarthritis in women, according to findings from two studies presented at the annual meeting of the American College of Rheumatology.

Specifically, strong quadriceps muscles protected the patellofemoral joint from cartilage loss and did not worsen its loss in the tibiofemoral joint in both men and women. Large leg muscle mass overall did not seem to influence x-ray progression of osteoarthritis (OA) in the patellofemoral joint, except for the medial aspect of the joint in women.

At a press briefing, Dr. Shreyasee Amin of the Mayo Clinic, Rochester, Minn., noted that strong quadriceps have been viewed as protective against knee OA. But some previous studies found evidence that greater quadriceps strength may do more harm than good in the tibiofemoral joint in mechanically malaligned knees.

But these earlier studies used x-rays to measure progression, which is an indirect measure of cartilage loss, the hallmark of OA. Pathologic changes to the meniscus on x-ray also can appear to increase joint-space narrowing, yet not reflect any real change in cartilage, she said.

Dr. Amin and colleagues performed MRI at baseline, 15 months, and 30 months, and measured quadriceps strength at baseline in 265 men and women with symptomatic knee OA. The patients had a mean age of 67 years and a mean body mass index (BMI) of 31.5 kg/[m.sup.2]. Upon dividing the patients into three levels of strength for each gender, the investigators found that men and women with the greatest quadriceps strength were 60% less likely to lose cartilage in the lateral aspect of the patellofemoral joint after 30 months than were those with the least strength.

"The quadriceps muscle could help stabilize the patella and prevent it from subluxing laterally, and so we feel that that might be a reason why greater quadriceps strength protects against cartilage loss at the lateral patellofemoral joint," she said.

MRIs showed no evidence that greater quadriceps strength either protected or worsened cartilage loss at other areas of the knee. Analyses were adjusted for age, BMI, gender, and baseline cartilage scores.

In a subgroup analysis of patients whose knees were measured for malalignment, varus alignment (bow leg) of 5 degrees or more did not increase tibiofemoral joint cartilage loss. There were too few with a valgus alignment (knock knee) of 5 degrees or more for analysis.

During a separate presentation, Dr. David J. Hunter of Boston University reported that a large amount of lean muscle mass in the leg had no effect on the x-ray progression of patellofemoral OA, after correcting for race, height, and total percentage of fat. But women with the largest muscle mass were more likely to experience progression of medial patellofemoral OA than were women with the least amount of leg muscle mass, even after adjusting for those confounding variables.

"I really want to emphasize that a lot of the effects that we saw with muscle mass were largely mitigated when we adjusted for total percent fat and race. The differences in prevalence [of joint space narrowing progression] were quite profound in this study, such that it was much more common in blacks, particularly in black women," Dr. Hunter said.

Dr. Hunter and associates measured OA progression with weight-bearing, skyline x-rays taken at baseline and after 36 months in 796 patients with and without knee pain on most days. The patients were originally part of a cohort of 3,075 white and black men and women aged 70-79 years in the multi-center, community-based Dynamics of Health, Aging, and Body Composition (Health ABC) study on knee OA.

In patients with large muscle mass, an increased pull of the vastus medialis oblique muscle, which would pull the patella medially, may increase the potential for medial patellofemoral joint space narrowing progression. Knee flexion force might also be increased in people with large leg muscle mass because of a large hamstring muscle, which could increase patellofemoral joint reaction force. Muscle mass also might be a proxy for physical activity, which itself may predispose toward progression, Dr. Hunter said.

BY JEFF EVANS

Senior Writer
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Title Annotation:Rheumatology
Author:Evans, Jeff
Publication:Internal Medicine News
Geographic Code:1USA
Date:Jan 1, 2007
Words:705
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