sinovial

Synovial, often spelled synovial in English, refers to the structures and fluids associated with the synovial joints. The term is also encountered as sinovial in some languages or as a common misspelling in English. It encompasses the membranes lining joints, the joint cavity, and the lubricating fluid within this space.

Anatomy: The joint capsule is lined on its inner surface by the synovial membrane, which has two layers: an intima composed of specialized cells known as synoviocytes and a subintima of loose connective tissue. The space inside the capsule, the synovial cavity, contains synovial fluid produced by the lining cells. This system can be accompanied by articular cartilage, which covers the ends of bones and is nourished by the fluid.

Function: The primary role of the synovial system is to reduce friction between articulating surfaces and to nourish avascular cartilage. Synovial fluid is viscous due to hyaluronic acid and lubricin, providing lubrication and boundary protection during movement. The membrane also participates in immune and inflammatory responses within the joint.

Joints: Synovial joints are diarthroses, characterized by a synovial cavity and a degree of joint mobility. They are classified into several types based on surface shape and movement: plane, hinge, pivot, condyloid, saddle, and ball-and-socket joints.

Clinical relevance: Inflammation of the synovial membrane, synovitis, is common in conditions such as rheumatoid arthritis and other inflammatory arthritides. Abnormal synovial fluid production or joint effusion can indicate infection, crystal arthropathies, or degenerative joint disease, and analysis of the fluid can aid diagnosis.