Joint Capsule
A tough, fibrous envelope that surrounds a joint, enclosing the joint space and containing synovial fluid. Its inner lining produces the fluid that lubricates the joint.
Extended Definition
The joint capsule is a critical structure that defines and protects the joint space. It consists of two distinct layers, each serving important functions for joint health and movement.
The outer layer, called the fibrous capsule, is made of tough, dense connective tissue that provides strength and stability to the joint. This layer attaches to the bones on either side of the joint and helps hold them together while still allowing movement. Ligaments—the bands that connect bone to bone—are often considered thickenings of this fibrous capsule.
The inner layer is the synovial membrane, a delicate tissue rich in blood vessels and nerves. This membrane produces synovial fluid, which fills the joint space and lubricates the cartilage surfaces. The synovial membrane also contains cells that help remove debris from the joint space and regulate inflammation.
In osteoarthritis, the joint capsule often becomes thickened and stiff, contributing to reduced range of motion. The synovial membrane may become inflamed (synovitis), producing excess fluid and inflammatory chemicals that can further damage joint tissues. Physical therapy and gentle stretching exercises can help maintain capsule flexibility and joint mobility.
Related Terms
More Anatomy Terms
View allAcetabulum
The cup-shaped socket of the pelvis that holds the head of the femur (thigh bone) in the hip joint.
Articular Cartilage
The smooth, white tissue covering the ends of bones in joints. Its breakdown is the primary feature of osteoarthritis.
Bursae
Small, fluid-filled sacs that act as cushions between bones, tendons, and muscles near joints, reducing friction during movement. Singular form is 'bursa.'
Bursa
Small, fluid-filled sacs that cushion bones, tendons, and muscles near joints. Bursitis (inflammation of a bursa) can cause joint pain similar to arthritis.
Cartilage
A smooth, rubbery connective tissue that covers and protects the ends of bones where they meet to form joints, allowing them to glide smoothly during movement.