Role of Infrapatellar Fat Tissue in the Pathogenesis of Knee Osteoarthritis: A Review

Abstract

Osteoarthritis (OA) is one of the most common joint diseases in the adult population. The role of indolent inflammation and predominance of catabolic cytokines over anabolic ones in OA has now been proven. The influence of obesity on the development of OA by releasing inflammatory mediators by fat tissue has been confirmed. Infrapatellar fat tissue (Hoffa’s fat pad) is a potential donor of proinflammatory cytokines, including specific fat tissue proinflammatory cytokines - adipokines. In a healthy person, infrapatellar fat tissue contributes to the distribution of mechanical load on the joint and metabolism of the synovial fluid. Infiltration of infrapatellar fat tissue by macrophages and lymphocytes leads not only to the production of proinflammatory cytokines with chondrolytic properties, but also to the maintenance of chronic inflammation in the synovial membrane, articular cartilage, and subchondral bone. Morphologic changes in Hoffa’s fat pad can be both an indicator of the inflammatory process in the joint cavity and a predictor of pathologic changes of the joint. Among histological changes, infiltration with macrophages and lymphocytes, fibrosis, thickening of the interlobular septa, reduction in the size of fat lobules and adipocytes, and increased vascularization are important for the course of OA. Morphologic changes can be assessed using a non-invasive method - magnetic resonance imaging, which makes it possible to evaluate the presence and severity of synovitis, thickening of the synovial membrane, edema, thickening of the interlobular septa, and a decrease in the volume of Hoffa’s fat pad. Histologic and tomographic signs can potentially be used to assess the severity of OA and develop prognostic scales. Infrapatellar fat tissue is also a source of mesenchymal stem cells phenotypically similar to chondrocytes, which can be used for regeneration of joint cartilage tissue with minimally invasive intervention to harvest them.

Keywords

• infrapatellar fat tissue
• hoffa’s fat pad
• knee osteoarthritis
• adipokines
• knee joint
• synovial membrane
• magnetic resonance imaging