Age-associated increases in the size of the infrapatellar fat pad in knee osteoarthritis as measured by 3T MRI.

Obesity, as a primary risk factor for osteoarthritis (OA), has been shown to alter joint loading, but may also result in metabolic changes characterized by chronic, low-level inflammation due to increased circulating levels of adipose-derived cytokines, or "adipokines." The presence of the infrapatellar fat pad in the knee suggests that local changes in adipokine concentrations may influence knee OA. This study examined the hypotheses that the volume of the infrapatellar fat pad is correlated to the body mass index (BMI) of OA patients, and that fat pad volume is greater in subjects with OA. Fat pad volume was measured in sequential magnetic resonance (MR) images taken over one year in a cohort of 15 control and 15 knee OA subjects. No differences were observed in the fat pad volume between the two groups at baseline, 3, 6, or 12 months. In control subjects, no significant correlations were present between any parameters (age, BMI, weight, volume of fat pad at any time point). However, in the osteoarthritic group, fat pad volume was correlated with age at every time point. One possible explanation is that local factors related to knee OA may also induce enlargement of the fat pad with age. Alternatively, subjects who are prone to growth or enlargement of the fat pad may also be more prone to symptomatic OA. These findings provide intriguing preliminary data on the potential role of the infrapatellar fat pad in OA, although additional study is required to better understand the mechanisms of this relationship.