Decreasing BMI May Reduce Progression of Knee Osteoarthritis

By Rebecca Araujo - March 30, 2023

Decreasing body mass index (BMI) was independently associated to reduced progression of knee osteoarthritis (OA) on radiography, according to a study in Arthritis & Rheumatology.

Being overweight (BMI 25 to <30 kg/m2) or obese (BMI ≥30.0 kg/m2) are known risk factors for the development and progression of knee OA, with nearly one-quarter of cases of new-onset knee pain or OA being attributed to excess weight. For this recent study, Zubeyir Salis and colleagues sought to use radiography to determine the association between BMI change and the progression of structural defects associated with knee OA.

The team utilized baseline and 4 to 5 years of follow-up data from 3 independent cohort studies: the Osteoarthritis Initiative (OAI) study, the Multicenter Osteoarthritis Study (MOST), and the Cohort Hip and Cohort Knee (CHECK) study. They used logistic regression analyses to investigate the association between change in BMI from baseline through follow-up and the corresponding incidence and progression of knee OA during that timeframe. Exclusion criteria included knee replacement surgery prior to baseline.

In total, 9,683 knees from 5,774 participants were included in an “incidence” cohort, and 6,075 knees from 3,988 participants were included in a “progression” cohort. The incidence cohort comprised knees with a baseline OA status of “none” or “doubtful.” The progression cohort consisted of knees that had minimal, moderate, or severe OA at baseline.

Incidence and progression of knee OA, as assessed by radiography, were defined according overall structural defects (assessed by Kellgren–Lawrence grade) and defects in 3 individual features of the knee, of the following: joint space narrowing, osteophytes on the femoral surface, and osteophytes on the tibial surface. Individual defects must occur on both the medial and the lateral side of the knee, as assessed by the Osteoarthritis Research Society International grade.

Based on their findings, the investigators reported that change in BMI was positively associated with both incidence and progression of knee OA. After adjustment, the odds ratio (OR) for incidence was 1.05 (95% confidence interval [CI] 1.02–1.09), and the OR for progression was 1.05 (95% CI 1.01–1.09). Each 1-unit decrease in BMI was associated with a 4.76% reduction in the odds of OA incidence and progression. In knees that were exposed to a BMI decrease of ≥5 units (an amount that can lead to a reduction in BMI category), there was a 21.65% reduction in the odds of incidence and progression. Change in BMI was positively associated with degeneration of the joint space and of the femoral and tibial surfaces (as indicated by osteophytes) on the medial side of the knee, although this relationship was not found for the lateral side.

Regarding the takeaway for clinicians, the authors wrote, “Our findings suggest that not only could decreasing BMI prevent or delay the incidence of knee degeneration in individuals who do not have knee defects, it could also prevent, delay, or slow the progression of knee degeneration for those in whom knee degeneration has already commenced.”

The study was limited by its observational nature and a lack of adjustment for history of knee injury—however, the authors added, “Our sensitivity analysis on the subset of participants for whom history of knee injury was available showed that knee injury had no significant effect on the results.” The authors additionally cited latent confounders that were not captured, such as decreased BMI due to decreased height with aging, the fact that BMI may have fluctuated during the study period, and the predominantly White and elderly patient population. The investigators called for further randomized controlled trials to confirm their findings.

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