Joint

A joint is the location at which two or more bones make contact.[1] They are constructed to allow movement (except for skull bones) and provide mechanical support, and are classified structurally and functionally. Classification Depiction of an intervertebral disk, a cartilaginous joint. Diagram of a synovial (diarthrosis) joint. Joints are mainly classified structurally and functionally. Structural classification is determined by how the bones connect to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications. Terms ending in the suffix -sis are singular and refer to just one joint, while -ses is the suffix for pluralization. [edit]Structural classification (Binding tissue) Structural classification names and divides joints according to the type of binding tissue that connects the bones to each other.[3] There are three structural classifications of joints:[4] fibrous joint - joined by dense irregular connective tissue that is rich in collagen fibers [5] cartilaginous joint - joined by cartilage synovial joint - not directly joined - the bones have a synovial cavity and are united by the dense irregular connective tissue that forms the articular capsule that is normally assoc ated with accessory ligaments.[5] [edit]Functional classification (movement) Joints can also be classified functionally according to the type and degree of movement they allow:[3][6] synarthrosis - permits little or no mobility. Most synarthrosis joints are fibrous joints (e.g., skull sutures). amphiarthrosis - permits slight mobility. Most amphiarthrosis joints are cartilaginous joints (e.g., intervertebral discs). diarthrosis - freely movable.[3][6] All diarthrosis joints are synovial joints (e.g., shoulder, hip, elbow, knee, etc.), and the terms "diarthrosis" and "synovial joint" are considered equivalent by Terminologia Anatomica.[7] Diarthroses can in turn be classified into six groups according to the type of movement they allow: arthrodia, enarthrosis, ginglymus, rotary diarthrosis,[8][9] condyloid articulation and articulation by reciprocal reception.[10] Joints can also be classified according to the number of axes of movement they allow, into monoaxial, biaxial and multiaxial.[11] Another classification is according to the degrees of freedom allowed, and distinguished between joints with one, two or three degrees of freedom.[11] A further classification is according to the number and shapes of the articular surfaces: flat, concave and convex surfaces.[11] Types of articular surfaces include trochlear surfaces.