Background There has been evidence that the well-known association between obesity and knee osteoarthritis (OA) is attributable not only to increased mechanical stress, but also to systemic metabolic effect of increased adiposity. Sarcopenic obesity (SO) is a body composition in which increase in adipose tissue is accompanied by decrease in skeletal muscle mass, offsetting the increase in body weight caused by increased adiposity.
Objectives This study aims to analyze the strength of association with radiographic knee OA in four different body compositions (normal (NO), sarcopenia (SP), non-sarcopenic obesity (OB) and SO), in order to evaluate whether SO is more closely associated with radiographic knee OA than OB, although body weight is expected to be comparable in the two conditions.
Methods A cross-sectional analysis was performed using data from 2893 participants (aged ≥50 years) of The Fifth Korean National Health And Nutrition Examination Survey (KNHENES V-1). Radiographic knee OA was defined as Kellgren-Lawrence grade of ≥2. Appendicular skeletal muscle mass (ASM) and total body fat mass was measured using dual energy X-Ray absorptiometry (DXA). SP was defined as skeletal muscle mass index (ASM/body weight, %) below -2 SD of sex-specific young reference group. OB was defined as BMI ≥27.5 kg/m2 (the cut-off associated with increased mortality in Asians). Participants who were both sarcopenic and obese were classified as SO. Those who were neither sarcopanic nor obese were classified as NO. The association between the presence of radiographic knee OA and the four body compositions, controlling for important confounding factors, was analyzed using logistic regression analysis.
Results Among the participants, the prevalence of each body composition was as follows; NO: 83.5%, SP: 4.3%, OB: 9.2% and SO: 3.0% At baseline, compared with participants with OB, participants with SO were older, had higher total body fat mass, higher abdominal circumference and lower ASM. (all differences, p-value <0.05). However, there was no significant difference in body weight (OB: 73.3±8.3 kg, SO: 73.1±9.6, p-value =0.997) or BMI (OB: 29.3±1.9 kg/m2, SO: 29.9±2.3, p-value =0.831) When adjusted for age, sex, smoking, alcohol consumption, muscle strengthening exercise, and presence of vitamin D insufficiency, SO was more closely associated with radiographic knee OA (OR: 3.92, 95% CI: 2.36 – 6.51, p-value <0.001) than OB (OR: 2.57, CI: 1.92 – 3.43, p-value <0.001). SP had no significant association with radiographic knee OA. (OR: 0.99, CI: 0.65 – 1.51, p-value: 0.965; NO: reference). The same analysis resulted in consistent findings in participants who had both symptomatic and radiographic knee OA, and in participants with radiographic knee OA who were ≥65 years old.
Conclusions SO was more closely associated with radiographic knee OA than OB, although both had equivalent body weight. This finding suggests the importance of systemic metabolic effect of obesity in knee OA.
Disclosure of Interest None Declared