what is a joint capsule

A joint capsule is a vital structure in the human body that surrounds a synovial joint. It is a dense fibrous connective tissue that is attached to the bones via specialized attachment zones at the end of each involved bone. The joint capsule has several important functions, including sealing the joint space, providing passive stability by limiting movements, and providing active stability via its proprioceptive nerve endings. It may also form articular surfaces for the joint and varies in thickness according to the stresses to which it is subject. The capsule is often injured, leading to laxity, constriction, and/or adhesion to surrounding structures. Additionally, the joint capsule is important in rheumatic diseases, including rheumatoid arthritis and osteoarthritis. It consists of two layers or membranes: an outer fibrous layer and an inner synovial layer. The outer layer is highly innervated and is made up of dense connective tissue. The joint capsule is a key component of synovial joints and plays a crucial role in their function and stability.