The Infrapatellar Adipose Body: A Histotopographic Study

Abstract

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.

Knee and hip intra-articular adipose tissues (IAATs) compared with autologous subcutaneous adipose tissue: a specific phenotype for a central player in osteoarthritis

“…According to the link between fibrosis, inflammation and mechanical load, we suggest that the peculiar phenotype of IAATs we describe here could depend on intrinsic properties of IAATs. A recent study comparing the histological characteristics of IFP from cadavers without knee OA to autologous knee SCAT and heterologous abdominal SCAT24 reported that IFP adipocytes were smaller than those from SCAT. However, their results on tissue fibrosis differ from ours.…”

Systemic and Local Adipose Tissue in Knee Osteoarthritis

“…). IFP is an extrasynovial but intracapsular adipose tissue attached to the intercondylar notch of femur by the IFP synovial plica (Macchi et al, ). Nonetheless, the exact role of IFP remains debated.…”

“…In fact, for its structural characteristics (lobular aspect of the adipose tissue, thickness of the septa with scarce elastic fibers Fig. ) (Macchi et al, ) IFP could act as a plastic portion aimed to absorption of pressure variations during knee articular activity (Macchi et al, ). However, recent evidence suggests that IFP might have not only a biomechanical ( Fontanella et al, ) but also a biochemical role in the pathogenesis of OA secreting inflammatory mediators like cytokines and adipokines (Clockaerts et al, ; Ioan‐Facsinay and Kloppenburg, ; Richter et al, ; Santangelo et al, ).…”

“…IFP structural changes are shown at cellular and histological levels in OA condition compare tothe normality. In healthy individuals IFP consists of white adipose tissue, organized in lobuli with thin interlobular septa as demonstrated by the microscopic picture (haematoxylineosin staining, scale bar: 1200 μm, taken from a subject involved in the Body Donation Program “Donation to Science” of the held by the University of Padova without history of osteoarthritis) (Macchi et al, ). On the contrary, the microscopic image (haematoxylin‐eosin, scale bar: 1200 μm) of IFP of an OA patient undergoing total knee replacement showed lymphocytic infiltration and thick interlobular septa.…”

The infrapatellar fat pad and the synovial membrane: an anatomo‐functional unit

“…Using immunohistochemistry, the IFP showed free nerve fibres and nerves surrounded by thick multilaminated (three to six layers) connective tissue capsule. The free nerve fibres were recognizable within adipose lobules, whereas the corpuscles were recognizable along the interlobular septa, in the adipose lobules and close to the vessels (Macchi et al 2016). Moreover, the presence of type VIa free nerve endings is particularly important, as they may initiate afferent signals of pain, pressure and thermic variations to the central nervous system (Biedert & Kernen, 2001).…”