Pain, Mechanical Properties, and MRI Characteristics of Infrapatellar and Suprapatellar Fat Pads in End-Stage Osteoarthritis

Osteoarthritis (OA) is a common degenerative joint disease affecting millions worldwide, with knee OA being highly prevalent. The disease, associated with various risk factors (e.g. obesity and previous injuries), causes pain and disability, leading to significant healthcare costs. This study focuses on the biomechanical role of two knee adipose tissues obtained from patients undergoing Total Knee Arthroplasty (TKA): the Infrapatellar (IFP) and Suprapatellar Fat Pads (SFP). Specifically, it aims to investigate and compare their mechanical behaviours in OA conditions, exploring the relationship between tissue volume, mechanical properties, and pain. This was achieved using an experimental procedure (stress relaxation and loading-unloading unconfined compression tests) combined with Magnetic Resonance Imaging (MRI) segmentation to obtain the Insall-Salvati ratio and tissue volume. MRI analyses showed significantly larger volumes for the IFP tissue than the SFP, and the experimental results revealed that the IFP had a higher elastic modulus than the SFP. A strong positive correlation was found between SFP peak stress and pain and elastic modulus and pain; the parameters increased with pain, suggesting a potential link between SFP mechanical behaviour and pain. In contrast, no correlation was found between IFP MRI data, mechanical parameters, and pain. The novel findings of this study highlight the complex role of knee adipose tissues in OA, particularly concerning the SFP, which has not yet been studied till now. These insights could be useful for improving TKA surgery techniques and developing computational models to enhance knee prosthesis design.