Synovial fluid is made of hyaluronic acid and lubricin, proteinases, and collagenases.

[15] Chiefly, it is responsible for so-called boundary-layer lubrication, which reduces friction between opposing surfaces of cartilage.

[16] It also contains phagocytic cells that remove microbes and the debris that results from normal wear and tear in the joint.

Synovial fluid may be collected by syringe in a procedure termed arthrocentesis, also known as joint aspiration.

In a normal specimen, this should lead to a congealing of the hyaluronic acid, forming a 'mucin clot.'

If inflammation is present, a mucin clot is not formed (the hyaluronic acid is degraded).

Microscopic analysis of synovial fluid is performed to evaluate for cell count and crystals.

The volume of synovial fluid within the joint is insufficient to fill the expanding volume of the joint and gases dissolved in the synovial fluid (mostly carbon dioxide) are liberated and quickly fill the empty space, leading to the rapid formation of a bubble.

[23][24] The term synovia (/sɪˈnoʊviə/) came to English around 1640 (the anglicized form synovial is first recorded in the mid 18th century) from Neo-Latin, where it was coined perhaps by Paracelsus from Greek συν- "with" and Latin ovum "egg" and -ia because it resembles egg white in consistency and external appearance.

[25][26][27][28][29] The term synovium is a much more recent pseudo-Latin coinage for what is less confusingly called the synovial membrane.