Weight Loss May Not Help Prevent Progression of Knee Osteoarthritis With Varus Alignment

Laurie Barclay, MD

March 13, 2009

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March 13, 2009 — Weight loss may not help prevent progression of knee osteoarthritis (OA) in patients with varus alignment, according to the results of a longitudinal study reported in the March 15 issue of Arthritis Care & Research.

"Obesity is a strong risk factor for incident (new-onset) tibiofemoral knee...OA," write J. Niu, from Boston University School of Medicine in Boston, Massachusetts, and colleagues. "However, in knees that already show evidence of OA, findings on the relationship between body mass index (BMI) and OA progression are inconsistent."

The goal of this study was to determine whether obesity is associated with an increased risk for progression of knee OA, using data from persons with or at high risk for knee OA who were enrolled in the Multicenter Osteoarthritis Study. At baseline and at 30 months, posteroanterior fixed-flexion radiographs and Kellgren/Lawrence (K/L) grading were used to characterize OA, defined as K/L grade 2 or 3. Alignment was determined on full-extremity films.

Progression in knees with OA at baseline was defined as tibiofemoral joint space narrowing on the 30-month radiograph. In knees without OA at baseline, defined as K/L grade 0 or 1, incident OA was defined as radiographic evidence of OA (K/L grade 2 or 3) at 30 months. Based on BMI at baseline, patients were classified as normal weight (< 25 kg/m2), overweight (25 to < 30 kg/m2), obese (30 to < 35 kg/m2), and very obese (> 35 kg/m2). The risk for progression was evaluated in all knees, as well as in subgroups based on alignment, and analyses were adjusted for age, sex, knee injury, and bone density.

The study sample consisted of 2623 subjects (5159 knees), of whom 60% were women and more than 80% were overweight or obese. Mean age was 62.4 ± 8.0 years.

At baseline, tibiofemoral OA was present in 36.4% of knees, of which only one third had neutral alignment. Compared with participants with a normal BMI, those who were obese or very obese had an increased risk for incident OA (relative risk, 2.4 and 3.2, respectively; P for trend < .001). This increased risk was present in knees from all alignment groups.

Overall, high BMI and the risk for OA progression were not significantly associated among knees with OA at baseline. However, the risk for progression was increased among knees with neutral, but not varus, alignment, and the effect of obesity was intermediate in those with valgus alignment.

Limitations of this study include evaluation at only 2 time points, analysis focused on structural (radiographic) progression and not on symptoms, and observational study design.

"Although obesity was a risk factor for incident knee OA, we observed no overall relationship between obesity and the progression of knee OA," the study authors write. "Obesity was not associated with OA progression in knees with varus alignment; however, it did increase the risk of progression in knees with neutral or valgus alignment. Therefore, weight loss may not be effective in preventing progression of structural damage in OA knees with varus alignment."

The National Institutes of Health and National Institute on Aging supported this study.

Arthritis Care Res. 2009;61:329-335.

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