The Infrapatellar Adipose Body: A Histotopographic Study

The infrapatellar fat pad (IFP) can be regarded as a peculiar form of fibro-adipose tissue localized close to the synovial membrane and articular cartilage. The aims of the present study were to analyze the microscopic anatomy of the IFP through histological and ultrastructural methods, comparing it with that of the subcutaneous tissue of the abdomen and of the knee. Ten specimens of IFP were sampled from bodies of the Donation Program of the University of Padua without a history of osteoarthritis. The IFP consisted of white adipose tissue, of lobular type, with lobules delimited by thin connective septa. The IFP lobule areas were smaller (p < 0.05) and the interlobular septa were thicker (p > 0.05) than those of subcutaneous tissues of the abdomen, whereas the IFP lobule areas were larger (p < 0.05) and the interlobular septa were thinner than those of the subcutaneous tissue of the knee (p < 0.05). The IFP adipocytes present a mean area of 3,708 ± 976 µm2 with a large intercellular space, whereas the mean area of the abdominal tissues was greater (6,082 ± 628 µm2; p < 0.05). At scanning electron microscopy the IFP adipocytes were covered by thick fibrillary sheaths, creating a basket around the adipocytes. The structural characteristics of the IFP (lobular aspect of the adipose tissue, thickness of the septa with scarce elastic fibers) could act as a plastic portion aimed at the absorption of pressure variation during knee articular activity. The extensive distribution of nerves suggests a possible role of the IFP as a mechanoreceptor, corresponding to a tridimensional connective mesh working in the proprioceptive regulation of the activity of the knee joint.