A painful and sometimes crippling disease characterized by progressive cartilage loss, osteoarthritis (OA) of the knee affects an estimated 6 percent of adults over age 30.
AT present, no treatments are available that have been shown to impede the destructive course of this disease, apart from knee replacement surgery. Numerous studies have shown that being overweight increases the risk of developing knee OA, whose sufferers, on average, tend to be heavy. While doctors routinely advise patients to lose weight, researchers have yet to affirm the benefits of weight loss to prevent ongoing joint deterioration.
To better understand the effect of body weight on the course of knee OA, researchers at Boston University focused on an important predictor of disease progression: limb malalignment, defined by joint space loss at the point where the thigh and shin bones connect to the knee. Featured in the December 2004 issue of Arthritis & Rheumatism, their findings suggest that the benefits of weight loss for knee OA patients depend on the degree of alignment in the affected leg.
The researchers recruited their subjects from two studies on quality of life conducted by the Veterans Administration of the Boston Health Care System. 228 individuals with knee OA were selected; all but one completed a 30-month period of follow-up. 41 percent were women and the mean age was 66 years. Among the subjects, the diagnosis of OA was confirmed by radiographs in 394 knees. At the first follow-up examination, each subject was assessed for degree of alignment in the affected leg, which was then categorized as moderate, severe, or neutral. Malaligned limbs could be either varus (bowlegged) or valgus (knock-kneed). The body mass index (BMI) of each subject was also computed.
Of the total 394 knees studied, 90 showed disease progression. Weight gain did have a significant impact. For each 2-unit increase in BMI, researchers found an 8 percent increase in the risk of disease progression. However, this effect was limited to knees in the moderately malaligned legs. In neutrally aligned legs on the one end of the spectrum and severely maligned legs on the other, body weight had no measurable effect on the risk of OA progression. "The effect of BMI on progression was different at different levels of alignment, with the risk being much greater for limbs with moderate malalignment," affirms the study's author, David T. Felson, M.D.