The biphasic role of the infrapatellar fat pad in osteoarthritis
Songkai Yue, Ganggang Zhai, Siyu Zhao, Xiaming Liang, Yunke Liu, Jia Zheng, Xiaoyang Chen, Yonghui Dong
Abstract
Osteoarthritis (OA) is a progressive degenerative disease resulting in joint deterioration. It is a whole organ disease characterized by cartilage degeneration and varying degrees of synovitis, involving pathological changes in all joint tissues, such as cartilage, subchondral bone, ligaments, meniscus, synovium, and infrapatellar fat pad (IPFP). IPFP is the largest adipose tissue structure in the knee joint and is composed of fat cells, immune cells and blood vessels. Moreover, IPFP is located close to the cartilage and bone surface so that it may reduce the impact of loading and absorb forces generated through the knee joint, and may have a protective role in joint health. IPFP has been shown to release various cytokines and adipokines that play pro-inflammatory and pro-catabolic roles in cartilage, promoting OA progression. Intra-articular injections of IPFP-derived mesenchymal stem cells and exosomes have been shown to reduce pain and prevent OA progression in patients with knee OA. Previous studies have shown that IPFP has a biphasic effect on OA progression. This article reviews the latest research progress of IPFP, discusses the role and mechanism of IPFP in OA, provide new intervention strategies for the treatment of OA. This article will also discuss the handling of IPFP during the procedure of total knee arthroplasty. • IPFP is the largest adipose tissue in the knee, and IPFP quality has been implicated as a marker to predicate knee OA. • IPFP can release inflammatory factors and adipokines, which participate in the pathophysiology of knee OA. • IPFP-MSCs have emerged a promising cell source for cartilage repair. However, the application of MSCs has been controversial. • Single-cell transcriptomic approaches demonstrate the presence of significant cellular heterogeneity in the IPFP. • Due to the biphasic nature of IPFP in OA, the decision to remove the IPFP at surgery should be treated with caution.