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The suprapatellar fat pad is an adipose tissue located in the anterior knee whose role in osteoarthritis is still debated. Considering that anatomy drives function, the aim of this histotopographic study was to investigate the specific morphological features of the suprapatellar fat pad versus the infrapatellar fat pad in the absence of osteoarthritis, for a broad comparative analysis. Suprapatellar fat pad and infrapatellar fat pad tissue samples (n = 10/group) underwent microscopical/immunohistochemical staining and transmission electron microscopy analysis; thus, tissue‐specific characteristics (i.e., vessels and nerve endings presence, lobuli, adipocytes features, septa), including extracellular matrix proteins prevalence (collagens, elastic fibers), were focused. Multiphoton microscopy was also adopted to evaluate collagen fiber orientation within the samples by Fast Fourier Transform (coherency calculation). The absence of inflammation was confirmed, and comparable counted vessels and nerve endings were shown. Like the infrapatellar fat pad, the suprapatellar fat pad appeared as a white adipose tissue with lobuli and septa of comparable diameter and thickness, respectively. Tissue main characteristics were also proved by both semithin sections and transmission electron microscopy analysis. The suprapatellar fat pad adipocytes were roundish and with a smaller area, perimeter, and major axis than that of the infrapatellar fat pad. The collagen fibers surrounding them showed no significant difference in collagen type I and significantly higher values for collagen type III in the infrapatellar fat pad group. Regarding the septa, elastic fiber content was statistically comparable between the two groups, even though more represented by the suprapatellar fat pad. Total collagen was significantly higher in the infrapatellar fat pad and comparing collagen type I and type III they were similarly represented in the whole cohort despite collagen type I appearing to be higher in the infrapatellar fat pad than in the suprapatellar fat pad and vice versa for collagen type III. Second harmonic generation microscopy confirmed through coherency calculation an anisotropic distribution of septa collagen fibers. From a mechanical point of view, the different morphological characteristics determined a major stiffness for the infrapatellar fat pad with respect to the suprapatellar fat pad. This study provides, for the first time, a topographic description of the suprapatellar fat pad compared to the infrapatellar fat pad; differences between the two groups may be attributed to a different anatomical location within the knee; the results gathered here may be useful for a more complete interpretation of osteoarthritis disease, involving not only cartilage but the whole joint. [ABSTRACT FROM AUTHOR]

Plantar adipose tissue is a connective tissue whose structural configuration changes according to the foot region (rare or forefoot) and is related to its mechanical role, providing a damping system able to adsorb foot impact and bear the body weight. Considering this, the present work aims at fully describing the plantar adipose tissue's behaviour and developing a proper constitutive formulation. Unconfined compression tests and indentation tests have been performed on samples harvested from human donors and cadavers. Experimental results provided the initial/final elastic modulus for each specimen and assessed the non-linear and time-dependent behaviour of the tissue. The different foot regions were investigated, and the main differences were observed when comparing the elastic moduli, especially the final elastic ones. It resulted in a higher level for the medial region (89 ± 77 MPa) compared to the others (from 51 ± 29 MPa for the heel pad to 11 ± 7 for the metatarsal). Finally, results have been used to define a visco-hyperelastic constitutive model, whose hyperelastic component, which describes tissue non-linear behaviour, was described using an Ogden formulation. The identified and validated tissue constitutive parameters could serve, in the early future, for the computational model of the healthy foot. [ABSTRACT FROM AUTHOR]

Objective. The infrapatellar fat pad (IFP) is considered a local producer of adipocytokines, suggesting a potential role in OA. The objective of this study was to evaluate the histopathological and molecular characteristics of OA IFPs compared with controls. Methods. The histopathological characteristics of IFPs were evaluated in patients undergoing total knee replacements and in control patients (without OA), considering the following parameters: presence of inflammatory cells, vascularization, adipose lobules dimension and thickness of the interlobular septa. Immunohistochemistry was performed to evaluate VEGF, monocyte chemotactic protein 1 (MCP-1) and IL-6 proteins. Quantitative real time PCR was performed to evaluate the expression levels of adipocytokines in the OA IFPs. Results. OA IFPs showed an increase in inflammatory infiltration, vascularization and thickness of the interlobular septa compared with controls. VEGF, MCP-1 and IL-6 proteins were higher in OA IFPs compared with in controls. Inflammatory infiltration, hyperplasia, vascularization and fibrosis were increased in OA IFP synovial membranes compared with in those of controls. VEGF protein levels were associated with an increased number of vessels in the OA IFPs, while MCP-1 and IL-6 protein levels were associated with higher grades of inflammatory infiltration. Leptin levels were positively correlated with adiponectin and MCP-1expression, while adiponectin positively correlated with peroxisome proliferative activated receptor gamma, MCP-1 and IFP vascularity. MCP-1 showed a positive correlation with peroxisome proliferative activated receptor gamma. IFP lobules dimensions were positively correlated with IL-6 expression and negatively with thickness of interlobular septa. VEGF mRNA levels were positively correlated with increased synovial vascularity. Conclusions: OA IFPs and synovial membranes are more inflamed, vascularized and fibrous compared with those of control patients (without OA). [ABSTRACT FROM AUTHOR]

The infrapatellar adipose body (Hoffa's fat pad, IFP) is situated between the patellar tendon, the femoral condyle and the tibial plateau. The IFP consists of lobules of white adipose tissue delimited by thin connective septa. The actual structural functionality of the IFP is debated and should pertain to a cushioning role in the knee joint, providing to distribute and to damp mechanical stresses during articular activity. The present study is aimed to analyze the correlation between histological configuration and mechanical properties of the IFP, compared to other adipose tissues, partially differentiated by composition and conformation. Histological and ultrastructural methods were exploited to analyze the microscopic anatomies of IFP, knee (KSF) and abdominal (ASF) subcutaneous fat tissues. Numerical micro-models of the different tissues were developed by using histo-morphometric data, as the size of adipose lobules, the thickness of the septa and their composition. Numerical analyses made it possible to evaluate the mechanical functionality of the different fat tissues considering the characteristic loading conditions, as compressive and shear actions. The results pointed out the actual mechanical relevance of IFP and KSF, while ASF exhibited different mechanical properties. Furthermore, the contribution of connective septa and adipose lobules to compressive and shear mechanical behavior was elucidated. This preliminary investigation represents the basis for biomechanical interpretation and the definition of more refined model to be developed on the acquisition of additional histological and morphometric data. [ABSTRACT FROM AUTHOR]

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 µm 2 with a large intercellular space, whereas the mean area of the abdominal tissues was greater (6,082 ± 628 µm 2 ; 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. [ABSTRACT FROM AUTHOR]

The plantar fat pad of the human foot is a specific tissue made up of adipose chambers enveloped by fibrous septa. Aging, pathology or trauma may affect its histo-morphological configuration and mechanical response. The correlation between histo-morphological configuration and mechanical properties is analyzed by a computational approach, aiming to identify the influence of degenerative phenomena on plantar fat pad mechanics. Finite element meso-models, as numerical model of an intermediate-length scale, are developed for healthy and degenerative conditions, considering the different properties that degenerative phenomena may affect, such as the adipose chambers dimension, the fibrous septa thickness, the fibers orientation and the sub-components mechanical behavior. Histo-morphometric data are analyzed to identify average configurations of the fat chambers and fibrous septa, while specific constitutive formulations are provided to define their mechanical response. Numerical analyses are performed to identify the stress-strain behavior of the plantar fat pad considering healthy and degenerative configurations. The results from meso-models are applied to identify the parameters of a phenomenological constitutive formulation that interprets the overall human fat pad tissue mechanics. The constitutive formulation is implemented within a 3D finite element model of the heel region that is applied to evaluate the influence of degenerative phenomena on the overall mechanical functionality of the foot. [ABSTRACT FROM AUTHOR]

The infrapatellar fat pad (IFP) is an adipose tissue present in the knee that lies between the patella, femur, meniscus and tibia, filling the space between these structures. IFP facilitates the distribution of the synovial fluid and may act to absorb impulsive actions generated through the joint. IFP in osteoarthritis (OA) pathology undergoes structural changes characterized by inflammation, hypertrophy and fibrosis. The aim of the present study is to analyze the mechanical behavior of the IFP in patients affected by end-stage OA. A specific test fixture was designed and indentation tests were performed on IFP specimens harvested from OA patients who underwent total knee arthroplasty. Experiments allowed to assess the typical features of mechanical response, such as non-linear stress–strain behavior and time-dependent effects. Results from mechanical experimentations were implemented within the framework of a visco-hyperelastic constitutive theory, with the aim to provide data for computational modelling of OA IFP role in knee mechanics. Initial and final indentation stiffness were calculated for all subjects and statistical results reveled that OA IFP mechanics was not significantly influenced by gender, BMI and sample preparation. OA IFP mechanical behavior was also compared to that of other adipose tissues. OA IFP appeared to be a stiffer adipose tissue compared to subcutaneous, visceral adipose tissues and heel fat pads. It is reasonable that fibrosis induces a modification of the tissue destabilizing the normal distribution of forces in the joint during movement, causing a worsening of the disease. [ABSTRACT FROM AUTHOR]

The suprapatellar fat pad (SFP) is located above the patella and behind the suprapatellar joint recess with the function of increasing the congruency of the extensor mechanism. Osteoarthritis SFP has been demonstrated to produce high amount of inflammatory molecules and to be more fibrous than subcutaneous adipose tissue in osteoarthritis (OA) patients. The aim of this study was to analyze 1. the morphological characteristics of the SFP compared to that of the infrapatellar fat pad (IFP) in normal subjects; 2. the magnetic resonance (MR) volumetric characteristics of the IFP and the SFP in non-OA controls compared to moderate and endstage OA patients. Five specimens of SFP were sampled from bodies of the donation program of the University of Padova without history of OA. The SFP consisted of white adipose tissue, of lobular type, with lobules delimited by thin connective septa. Forty-four MR images were collected: a) 17 control; b) 15 patients with moderate OA ; and c) 12 patients with end-stage OA. Volume, depth, femoral and tibial arch lengths of IFP were quantified. The SFP volume, oblique, antero-posterior and, cranio-caudal lengths were determined. A decrease of IFP volume, depth, femoral, and tibial arch lengths in moderate and end-stage OA compared to controls were observed. A difference in IFP hypointense signal was found between groups. No differences were found in SFP characteristics between the groups. In controls and moderate OA patients, correlations were found among the different MRI characteristics of both IFP and SFP, while in the end-stage OA group correlations were found only in SFP. Differences of the IFP MRI morphometric characteristics between the groups analyzed supports an important role of IFP in OA pathology and progression. On the contrary, no differences were highlighted in SFP analysis suggesting that this fat pad is not clearly involved in OA, probably due to its peculiar localization and different function. [ABSTRACT FROM AUTHOR]