Synovial membrane

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Synovial joints are the main type of joints found in the body.

The synovial membrane refers to a specialized type of connective tissue which lines the inner surfaces of synovial joint capsules, tendon sheaths and bursae. Its primary role is to secrete the lubricant synovial fluid.

Within the joint capsule, the synovial membrane lines all internal surfaces not covered by cartilage as well as intracapsular ligaments. It has a pink shiny appearance with folds that extend into some areas of the joint cavity.

The synovial membrane is composed of two distinct layers: a cellular, intimal layer which is supported by a fibrovascular subintimal layer (subsynovial tissue).

In some large synovial joint capsules, such as that of the knee, the synovial membrane may be continuous with the synovial lining of adjacent bursae. In addition, closed sacs of synovial membrane may also be found outside joint capsules. These form the synovial bursae located between various structures such as tendons and bone, or tendon sheaths surrounding tendons to reduce friction.

Synovial membrane cells produce synovial fluid, which is derived from blood plasma. It contains a high concentration of hyaluronan, believed to be responsible for its unique properties. Synovial fluid serves to lubricate and nourish the articular cartilage, as well as to evenly distribute pressure forces across the articular surfaces.