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Although results were associative rather than causative, a decrease in BMI may prevent, delay, or slow the structural defects in knee osteoarthritis.
A body mass index (BMI) decrease was associated with both lower odds of onset as well as progression of structural defects in patients with knee osteoarthritis, as determined by radiography. These results suggest that weight could be a factor in preventing the development and/or worsening of the condition, according to a study published in Arthritis & Rheumatology.1
“Overweight and obesity are risk factors for both the incidence and progression of knee osteoarthritis, with nearly 25% of cases of new-onset knee pain or osteoarthritis attributable to excess weight,” investigators explained. “A critical question is whether weight loss can mitigate these problems. Clinically, weight loss in people with knee osteoarthritis reduces knee pain, improves knee function, and enhances quality of life, but it is unclear whether weight loss mitigates the structural defects of knee osteoarthritis.”
Radiographic analyses of knees at baseline and a 4- to 5-year follow up were collected from the Osteoarthritis Initiative (OAI), Cohort Hip and Cohort Knee (CHECK), and Multicenter Osteoarthritis Study (MOST). Logistic regression analyses examined the association between changes in BMI (in kg/m2) and the incidence and progression of knee osteoarthritis.
In total, 9683 knees (5774 patients) were placed in the “incidence” cohort and 6075 knees (3988 patients) were in the “progression” cohort. Incidence was defined as knees that had an osteoarthritis status at baseline of either “none” or “doubtful.” Patients in the progression group had knees with an osteoarthritis status of “minimal,” “moderate,” or “severe” at baseline.
During the follow-up period, 12.6% (n = 1217) of knees in the incidence group developed structural defects of knee osteoarthritis, although 18.9% of the cohort had missing data on Kellgren-Lawrence (KL) grade at follow-up. In the progression cohort, 15% (n = 908) knees progressed by at least 1 KL grade in structural defects at follow-up (29.6% missing KL data).
In both the incidence and progression cohorts, 36.7% and 34.8%, respectively, reported changes in BMI between baseline and follow up of less than 1 BMI unit. However, 19.0% and 20.0% experienced a decrease of at least 1 unit in BMI and 44.3% and 45.2% experienced an increase of at least 1 unit in BMI in the incidence and progression cohorts, respectively.
Changes in BMI were positively associated with both onset and progression of structural defects in the adjusted models. The adjusted odds ratio (OR) of incidence was 1.05 (95% confidence interval [CI] 1.02 to 1.09) and progression was 1.05 (95% confidence interval [CI] 1.01 to 1.09). Reducing BMI by 1-unit resulted in a 4.76% decrease in incidence and progression. Further, a 5-unit reduction was linked to a 21.65% decrease in the risk of knee osteoarthritis onset and progression. Changes were also positively associated with degeneration of joint space and degeneration of the femoral and tibial surfaces on the medial side of the knee in both cohorts.
The observational nature of the study was inherently limiting, as results could only be viewed as associative rather than causative. Further, the primary multivariable analyses were not adjusted for history of knee injury. BMI may have been slightly affected by a decrease in height due to aging; however, the sensitively analysis confirmed that height decreases were not a confounding factor in the results. Investigators also noted that changes in BMI fluctuations between baseline and follow-up were not captured. Finally, generalizability may be difficult as patients enrolled in the 3 studies were predominantly White and elderly.
“While we showed evidence of association, not causality, people with overweight or obesity –and potentially also those of normal weight – may benefit from a decrease in BMI to prevent, delay, or slow the structural defects in knee osteoarthritis,” investigators concluded.
Salis Z, Gallego B, Nguyen TV, Sainsbury A. Decrease in body mass index is associated with reduced incidence and progression of the structural defects of knee osteoarthritis: a prospective multi-cohort study [published online ahead of print, 2022 Aug 16]. Arthritis Rheumatol. 2022;10.1002/art.42307. doi:10.1002/art.42307