Figure 1.

Overview of knee macro- and microanatomy. (Right) Sagittal cut through a human knee. The femur and tibia articulate in the tibiofemoral joint, with two fibrocartilaginous menisci serving to provide rotational and anterior-posterior stability and load distribution. The patella is a hypomochlion (pivot point) for the quadriceps tendon that articulates with the femur in the patellofemoral joint. The intra-articular components of the osseous structures are covered by cartilage, enabling low-friction bearing. Joint function and stability are maintained by ligaments and the joint capsule. The inner surface of the joint capsule is lined with the synovial membrane, which is accompanied by adipose tissues located intra-articularly and extra-synovially, including the infrapatellar fat pad. (Left, top) Microanatomy of subchondral bone. The cellular components of bone include osteoblasts, osteoclasts and osteocytes that dynamically respond to changes in mechanical loading and potentially communicate with the overlying cartilage via soluble signals. (Left, bottom) Microanatomy of the synovial membrane. The synovium comprises three layers: the intimal lining layer which consists of macrophages and fibroblasts that together form a semi-permeable protective barrier; the vascularized subintimal or sublining layer which contains interstitial macrophages and fibroblasts as well as adipocytes; and an outer fibrous stromal layer forming the joint capsule (not shown). Created with BioRender.com and smart.servier.com.