a delicate, thin inner layer that constitutes part of the articular capsule
of a synovial joint
. The synovial
membrane, also known as the synovium, is highly vascular
and lines the nonarticular portion of the synovial
joint, any intra-articular ligaments or tendons, and the intracapsular bone surfaces, which are clothed by periosteum or perichondrium but are without cartilaginous surfaces (the "marginal" or "bare" areas of the joint). Small finger-like projections, termed synovial
villi may be present on its inner surface.
The synovial membrane varies in structure in different parts of the joint. Although in general, the membrane exists in two synovial layers (a thin cellular surface layer or intima and a deeper vascular underlying layer or subintima), in some locations membrane is attenuated and two distinct layers cannot be differentiated. In the knee joint, the synovial membrane is especially elaborate and can be divided into a central portion, a suprapatellar synovial pouch, a posterior femoral recess and a subpopliteal recess.
Among the functions of this membrane are the secretion of a sticky mucoid substance into the synovial fluid; facilitation of and accommodation to the changing shape of the articular cavity required for normal joint motion; and assistance in the removal of substances from the articular cavity. The synovial membrane reveals abnormal changes in numerous pathologic conditions; several representative examples are listed in Table 1.
Synovial membrane, Table 1. Some histological findings on synovial membrane biopsy.