Synovial membrane

The thin line of tissue in the lower part of this view is the synovial membrane, which is essentially a continuation of the bone lining cell layer shown in other sections of bone and connective tissue and which lines the joint space in the knee joint. Fatty connective tissue is in the upper part of the section. F4/80-positive macrophages (type A synovial cells) can be seen interdigitated with F4/80-negative fibroblasts (type B cells). Occasionally the synovium can be seen in flat section (not shown), and the cells spread in a similar way to those on the bone surface in the figure of "Surface of bone".