Abstract
The infrapatellar fat pad (IFP) is actively involved in knee osteoarthritis (OA). However, a proper description of which developmental modifications occur in the IFP along with age and in absence of joint pathological conditions, is required to adequately describe its actual contribution in OA pathophysiology. Here, two IFP sources were compared: (a) IFP from healthy young patients undergoing anterior-cruciate ligament (ACL) reconstruction for ACL rupture (n = 24); (b) IFP from elderly cadaver donors (n = 23). After histopathological score assignment to confirm the absence of inflammatory features (i.e., inflammatory infiltrate and increased vascularity), the adipocytes morphology was determined; moreover, extracellular matrix proteins were studied through histology and Second Harmonic Generation approach, to determine collagens content and orientation by Fast Fourier Transform and OrientationJ. The two groups were matched for body mass index. No inflammatory signs were observed, while higher area, perimeter, and equivalent diameter and volume were detected for the adipocytes in the elderly group. Collagen III displayed higher values in the young group and a lower total collagen deposition with aging was identified. However, collagen I/III ratio and the global architecture of the samples were not affected. A higher content in elastic fibers was observed around the adipocytes for the ACL-IFPs and in the septa cadaver donor-IFPs, respectively. Age affects the characteristics of the IFP tissue also in absence of a pathological condition. Variable mechanical stimulation, depending on age-related different mobility, could be speculated to exert a role in tissue remodeling.
Highlights
Age represents the strongest predictor of development for the most common musculoskeletal disorder worldwide: osteoarthritis (OA) [1,2,3,4], a disease of great impact, especially in the light of the World Population Prospects report data [5] dreading a great shift in demographics
The time between injury and surgery of patients with anterior-cruciate ligament (ACL) rupture was at least 6 months
After confirmation of no inflammatory signs in all samples, the study results proved the initial assumptions related to infrapatellar fat pad (IFP) cells and extracellular matrix (ECM)
Summary
Age represents the strongest predictor of development for the most common musculoskeletal disorder worldwide: osteoarthritis (OA) [1,2,3,4], a disease of great impact, especially in the light of the World Population Prospects report data [5] dreading a great shift in demographics. To date there are about 962 million individuals over the age of 60 which will rise, reaching 1.4 billion in 2030 and 2.1 billion in 2050. When referring to individuals of 80 years old or over (today 137 million), a growing of 32.2% is expected for 2050 [5]. To figure out the role of a tissue in a pathological condition, a fine understanding of its physiological-developmental characteristics is mandatory. Homeostasis maintenance is an age-dependent event; according to a biological perspective, from aging descends a progressive decline in tissue physiological homeostasis provoking an increased impaired function. Age-related mobility disability has largely been attributed to compromised skeletal muscle characteristics [6, 7] or cartilage alterations [2]. Adipose tissue features (e.g., cellular composition and secreted factors) likely play a critical role in this process [6] and, considering synovial joints, adipose tissue is both recognized in the sub-synoviocyte intimal layer and in the periarticular depots of the knee joint, like the infrapatellar fat pad (IFP) that consists in white adipose tissue [8]
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