Type A cells maintain the synovial fluid by removing wear-and-tear debris.

This membrane, together with the cells of the intima, provides something like an inner tube, sealing the synovial fluid from the surrounding tissue (effectively stopping the joints from being squeezed dry when subject to impact, such as running).

Surface cells have no basement membrane or junctional complexes denoting an epithelium despite superficial resemblance.

Virtually all the space between muscles, ligaments, bones, and cartilage is filled with pliable solid tissue.

These may include: Synovium can become irritated and thickened (synovitis) in conditions such as osteoarthritis,[6] Ross River virus[7] or rheumatoid arthritis (RA).

Excessive thickened synovium, filled with cells and fibrotic collagenous tissue, can physically restrict joint movement.

The synovial fibroblasts may make smaller hyaluronan so it is a less effective lubricant of the cartilage surfaces.