Mechanical insights into fat pads: a comparative study of infrapatellar and suprapatellar fat pads in osteoarthritis

Osteoarthritis (OA) is the most common musculoskeletal disorder, primarily affecting knee joints and causing pain and disability. The infrapatellar (IFP) and the suprapatellar (SFP) fat pad are knee adipose tissues that play essential mechanical roles during articular activity but are also sources of adipokines and cytokines, contributing to OA progression. For this reason, this work aims to provide new insights into IFP and SFP implications in knee OA. IFP and SFP tissue mechanical properties were studied through compression, indentation and shear mechanical tests performed on samples collected from patients who underwent total knee arthroplasty surgery due to end-stage OA. The energy loss, peak stress, and initial and final elastic moduli were calculated from the unconfined compression tests. The time-dependent response, evaluated in terms of equilibrium relative stiffness, was computed from stress-relaxation loading conditions. Considering shear tests, they provided strain-energy dissipation density, peak shear stress, and the shear moduli. Experimental results showed the typical adipose tissue mechanics features: non-linear stiffening with strain and time-dependent response. Experimental results showed that OA IFP is stiffer than OA SFP, indeed IFP final compression elastic modulus was greater than the SFP (84.43 kPa vs 35.54 kPa respectively) (<i>p</i> = 0.042). Regarding the viscoelastic properties they were comparable: the equilibrium relative stiffness was reported as 0.13 for IFP and 0.11 for SFP (<i>p</i> = 0.026). These outcomes provide new insights into the OA influence on knee mechanics and lay the basis for developing computational tools to improve knee prosthesis design.

骨关节炎（Osteoarthritis, OA）是最常见的肌肉骨骼疾病，主要累及膝关节，引发疼痛与功能障碍。髌下脂肪垫（infrapatellar, IFP）与髌上脂肪垫（suprapatellar, SFP）作为膝关节脂肪组织，在关节活动中发挥关键机械作用，同时也是脂肪因子与细胞因子的来源，可促进骨关节炎进展。为此，本研究旨在深入解析髌下脂肪垫与髌上脂肪垫在膝关节骨关节炎中的作用，为相关领域提供新的研究视角。本研究针对因终末期骨关节炎接受全膝关节置换术的患者术中采集的脂肪垫样本，通过压缩、压痕与剪切力学试验，对髌下脂肪垫与髌上脂肪垫的力学性能展开研究。从无侧限压缩试验中，研究人员计算得到了能量损失、峰值应力以及初始与最终弹性模量；基于应力松弛加载工况，通过平衡相对刚度指标评估了样本的时间依赖性响应；剪切试验则获取了应变能量耗散密度、剪切峰值应力与剪切模量。试验结果显示，脂肪组织具有典型的力学特性：随应变呈现非线性硬化，且存在时间依赖性响应。研究发现，骨关节炎患者的髌下脂肪垫刚度高于髌上脂肪垫：其最终压缩弹性模量分别为84.43 kPa与35.54 kPa（*p*=0.042）。二者的黏弹性特性则较为相近，平衡相对刚度分别为0.13与0.11（*p*=0.026）。本研究结果为解析骨关节炎对膝关节力学特性的影响提供了新的认知，并为开发用于优化膝关节假体设计的计算工具奠定了基础。