Figure 1.

The comparison between normal joint and osteoarthritic joint Normal joint composed of joint cartilage, joint capsule, synovial membrane and articular cavity. Generally, synovial membrane has two layers. The inner layer, also called lining layer is mainly composed of synovial macrophage and synovial fibroblasts. The outer layer of synovial membrane also called sublining layer is connective tissue composed of blood vessels, collagens, interstitial macrophages, fibroblasts, adipocytes and a small number of lymphocytes. In osteoarthritic joint, the articular cartilage is damaged and the fragments of cartilage drift into articular cavity, forming loose bodies. The loss of cartilage leads to unevenly distributed loads on subchondral bones which can further cause osteoproliferation and sclerosis in the friction part as well as bone resorption and cystic degeneration in the periphery part. Moreover, both synovial membrane and articular capsule thicken in osteoarthritic joint due to inflammation. In hyperplastic synovial membrane, the most prominent changes are the hyperplasia of synovial and interstitial macrophages, the infiltration of T lymphocytes in sublining layer and the proliferation of blood vessels.