medwireNews: A reduction in BMI is associated with a lower risk for onset and progression of the structural defects of knee osteoarthritis (OA), indicate findings from a multicohort study.
Zubeyir Salis (University of New South Wales, Sydney, Australia) and co-authors evaluated radiographic data from three cohorts – namely the Osteoarthritis Initiative, the Multicenter Osteoarthritis Study, and the Cohort Hip and Cohort Knee study – and categorized people according to whether or not they had structural defects at baseline.
Among 9683 knees with a Kellgren–Lawrence (KL) score of 0 or 1 points at baseline (incidence cohort), 12.6% developed new-onset structural defects during 4–5 years of follow-up, defined as a KL score of at least 2 points. And among the 6075 knees with a KL score of at least 2 points at baseline (progression cohort), 15.0% increased by at least one KL grade during follow-up, indicating structural OA progression.
Salis and team report that approximately 45% of knees in the incidence and progression cohorts were exposed to a BMI increase of at least 1 kg/m2 during follow-up, while approximately 20% were exposed to a decrease of the same magnitude, and around 5% were exposed to a decrease of at least 3 kg/m2.
In an analysis adjusting for factors including baseline BMI, baseline KL score, comorbidities, and physical activity, each 1 kg/m2 reduction in BMI during follow-up was associated with a 4.76% decrease in the risk for onset or progression of knee OA structural defects.
While the researchers acknowledge that the magnitude of this association “can be considered weak,” they also found that a 5 kg/m2 decrease in BMI – “which is an amount that can lead to a reduction in BMI category (e.g., from overweight to normal)” – was associated with a 21.65% reduced risk.
Therefore, “decrease in BMI could be an intervention to prevent, delay or slow the structural defects of knee osteoarthritis,” they write in Arthritis & Rheumatology.
Salis et al note that these associations were seen in both people with overweight or obesity and in those with a healthy bodyweight at baseline, but caution that “the potential benefits of a decrease in BMI need to be considered alongside the potential dangers of weight loss in people of normal BMI.”
The team also evaluated the association between changing BMI and individual structural features of the knee. In the incidence cohort, BMI reduction was associated with a significant decrease in joint space narrowing and degradation of the tibial and femoral surfaces in the medial, but not the lateral, side of the knee.
“This finding is in line with literature showing that higher rates of cartilage loss generally occur on the medial [rather] than on the lateral side of the knee in people with knee osteoarthritis, and that the medial side of the knee carries more force from weight than the lateral side of the knee,” write the investigators.
They observed a similar association for medial joint space narrowing in the progression cohort, but not for degradation of the tibial and femoral surfaces.
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