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.

Keywords:
Adipocytes, Morphometry, Microscopic anatomy, Knee, Hoffa’s fat pad
1.
Bohnsack, M., P. Klages, C. Hurschler, A. Halcour, A. Wilharm, S. Ostermeier, O. Rühmann, C.J. Wirth (2009) Influence of an infrapatellar fat pad edema on patellofemoral biomechanics and knee kinematics: a possible relation to the anterior knee pain syndrome. Arch Orthop Trauma Surg 129: 1025-1030.
2.
Cinti, S. (1999) The Adipose Organ. Milan, Kurtis.
3.
Clockaerts, S., Y.M. Bastiaansen-Jenniskens, J. Runhaar J, G.J. van Osch, J.F. van Offel, J.A. Verhaar, L.S. De Clerck, J. Somville (2010) The infrapatellar fat pad should be considered as an active osteoarthritic joint tissue: a narrative review. Osteoarthritis Cartilage 18: 876-882.
4.
Davies, D.V., J.E. White (1961) The structure and weight of synovial fat pads. J Anat 95: 30-37.
5.
Divoux, A., J. Tordjman, D. Lacasa, N. Veyrie, D. Hugol, A. Aissat, A. Basdevant, M. Guerre-Millo, C. Poitou, J.D. Zucker, P. Bedossa, K. Clément (2010) Fibrosis in human adipose tissue: composition, distribution, and link with lipid metabolism and fat mass loss. Diabetes 59: 2817-2825.
6.
Freeman, M.A., B. Wyke (1967) The innervation of the knee joint. An anatomical and histological study in the cat. J Anat 101: 505-532.
7.
Gardner, E. (1948) The innervation of the knee joint. Anat Rec 101: 109-130.
8.
Giordano, A., A. Frontini, S. Cinti (2008) Adipose organ nerves revealed by immunohistochemistry. Methods Mol Biol 456: 83-95.
9.
Giordano, A., I. Murano, E. Mondini, J. Perugini, A. Smorlesi, I. Severi, R. Barazzoni, P.E. Scherer, Cinti S (2013) Obese adipocytes show ultrastructural features of stressed cells and die of pyroptosis. J Lipid Res 54: 2423-2436.
10.
Guidolin, D., E. Zunarelli, S. Genedani, G.P. Trentini, C. De Gaetani, K. Fuxe, C. Benegiano, L.F. Agnati (2008) Opposite patterns of age-associated changes in neurons and glial cells of the thalamus of human brain. Neurobiol Aging 29: 926-936.
11.
Hoffa, A. (1904) The influence of the adipose tissue with regard to the pathology of the knee joint. JAMA 43: 795-796.
12.
Hunter, D.J., D.T. Felson (2006) Osteoarthritis. BMJ 332: 639-642.
13.
Ioan-Facsinay, A., M. Kloppenburg (2013) An emerging player in knee osteoarthritis: the infrapatellar fat pad. Arthritis Res Ther 15: 225.
14.
Khan, T., E.S. Muise, P. Iyengar, Z.V. Wang, M. Chandalia, N. Abate, B.B. Zhang, P. Bonaldo, S. Chua, P.E. Scherer (2009) Metabolic dysregulation and adipose tissue fibrosis: role of collagen VI. Mol Cell Biol 29: 1575-1591.
15.
Krenn, V., S. Hofmann, A. Engel (1990) First description of mechanoreceptors in the corpus adiposum infrapatellare of man. Acta Anat (Basel) 137: 187-188.
16.
Macchi, V., A. Porzionato, C. Stecco, C. Tiengo, A. Parenti, A. Cestrone, R. De Caro (2011) Body parts removed during surgery: a useful training source. Anat Sci Educ 4: 151-156.
17.
Macchi, V., C. Tiengo, A. Porzionato, L. Busetto, A. Morra, R. Martini, F. Bassetto, R. De Caro (2014a) Anatomical remodelling of the anterior abdominal wall arteries in obesity. Clin Hemorheol Microcirc 57: 255-265.
18.
Macchi, V., C. Tiengo, A. Porzionato, C. Stecco, G. Sarasin, S. Tubbs, N. Maffulli, R. De Caro (2014b) The cubital tunnel: a radiologic and histotopographic study. J Anat 225: 262-269.
19.
Macchi, V., C. Tiengo, A. Porzionato, C. Stecco, E. Vigato, A. Parenti, B. Azzena, A. Weiglein, F. Mazzoleni, R. De Caro (2010) Histotopographic study of the fibroadipose connective cheek system. Cells Tissues Organs 191: 47-56.
20.
Moverley, R., D. Williams, N. Bardakos, R. Field (2014) Removal of the infrapatellar fat pad during total knee arthroplasty: does it affect patient outcomes? Int Orthop 38: 2483-2487.
21.
Panettiere, P., D. Accorsi, L. Marchetti, A.M. Minicozzi, G. Orsini, P. Bernardi, D. Benati, G. Conti, A. Sbarbati (2011) The trochanteric fat pad. Eur J Histochem 55: e16.
22.
Pasarica, M., B. Gowronska-Kozak, D. Burk, I. Remedios, D. Hymel, J. Gimble, E. Ravussin, G.A. Bray, S.R. Smith (2009) Adipose tissue collagen VI in obesity. J Clin Endocrinol Metab 94: 5155-5162.
23.
Pinsornsak, P., K. Naratrikun, S. Chumchuen (2014) The effect of infrapatellar fat pad excision on complications after minimally invasive TKA: a randomized controlled trial. Clin Orthop Relat Res 472: 695-701.
24.
Polacek, P. (1961) Differences in the structure and variability of encapsulated nerve endings in the joints of some species of mammals. Acta Anat 47: 112-124.
25.
Russ, J.C. (2011) The Image Processing Handbook, ed. 6. Boca Raton, Taylor & Francis Group.
26.
Sbarbati, A., D. Accorsi, D. Benati, L. Marchetti, G. Orsini, G. Rigotti, P. Panettiere (2010) Subcutaneous adipose tissue classification. Eur J Histochem 54: e48.
27.
Schneider, C.A., W.S. Rasband, K.W. Eliceiri (2012) NIH Image to ImageJ: 25 years of image analysis. Nat Methods 9: 671-675.
28.
Smillie, I.S. (1974) Disease of the Knee Joint, ed. 1. London, Churchill Livingstone.
29.
Spencer, M., R. Unal, B. Zhu, N. Rasouli, R.E. McGehee Jr., C.A. Peterson, P.A. Kern (2011) Adipose tissue extracellular matrix and vascular abnormalities in obesity and insulin resistance. J Clin Endocrinol Metab 96: E1990-E1998.
30.
Standring, S., N.R. Borley, P. Collins, A.R. Crossman, M.A. Gatzoulis, J.C. Healy, D. Johnson, V. Mahadevan, R.L.M. Newell, C.B. Wigley (eds) (2008) Gray's Anatomy, ed. 40. London, Churchill Livingstone, p 1395.
31.
Sund, S., P. Grimm, A.V. Reisaeter, T. Hovig (2004) Computerized image analysis vs. semiquantitative scoring in evaluation of kidney allograft fibrosis and prognosis. Nephrol Dial Transplant 19: 2838-2845.
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2016
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