Variance in infra-patellar fat pad volume: Does the body mass index matter?-Data from osteoarthritis initiative participants without symptoms or signs of knee disease.

The infra-patellar fat pad (IPFP) has been proposed to represent an endocrine link between obesity and knee osteoarthritis (OA). The purpose of the current study has been to explore the extent to which IPFP volume is related to body mass index (BMI). A total of 152 participants (age 56±7 years) without knee OA were studied. These consisted of 19 men and 19 women of normal weight (BMI 18.5-25), 19/19 pre-obese (BMI 25-30), 19/19 obese class I (BMI 30-35) and 19/19 obese class II (BMI 35-40), who were matched 1:1 for age and height. The IPFP volume was manually segmented from sagittal fat-suppressed magnetic resonance images (MRI). An ANOVA of repeated measures was used to assess whether IPFP volume was related to BMI. The IPFP volume differed significantly between the BMI strata (ANOVA: p=0.001): It was 27.1±6.7cm (mean±SD) in normal weight, 29.3±6.9cm in pre-obese, 31.0±6.9cm in obese class I, and 30.4±6.6cm in obese class II participants; the difference in IPFP volume (and body weight) relative to normal weight subjects was 10% (18%) in pre-obese, 17% (39%) in obese class I, and 15% (59%) in obese class II participants. Stratification by sex showed similar results. In conclusion, IPFP volume is shown to be related to BMI, albeit the relative increase (compared with normal weight) does not appear to be proportional to that in body weight. Nonetheless, these findings support the hypothesis that the IPFP may represent a potential endocrine link between obesity and OA, with more intra-articular adipose tissue potentially releasing greater amounts of adipokines.