Joint

A joint is a junction between two or more rigid elements that allows for movement or provides stability. In human anatomy, joints connect bones and other skeletal components, enabling a range of motions and load transmission. Joints are commonly categorized by their degree of movement into immobile (synarthroses), slightly movable (amphiarthroses), and freely movable (diarthroses).

Structurally, joints are classified as fibrous, cartilaginous, or synovial. Fibrous joints are bound by dense connective tissue and typically permit little or no movement, as in skull sutures. Cartilaginous joints connect bones by cartilage and allow limited motion, such as the pubic symphysis or intervertebral joints. Synovial joints feature a joint cavity, articular cartilage, and a synovial membrane within a joint capsule, with synovial fluid that lubricates the joint. They are reinforced by ligaments and may include structures such as menisci or bursae to improve stability and function.

Common synovial joints illustrate various movements: hinge joints (such as the knee and elbow) enable flexion and extension; ball-and-socket joints (shoulder and hip) permit multi-directional movement; pivot joints (proximal radioulnar) allow rotation; saddle and condyloid joints provide combinations of movements; plane joints permit gliding. Skull sutures are examples of fibrous immobile joints, while the temporomandibular joint is a movable, combined joint.

Joint disorders and injuries include osteoarthritis, rheumatoid arthritis, gout, sprains, and dislocations, which can affect function and cause pain. Management ranges from physical therapy and medications to surgical intervention in some cases. The term joint also appears in everyday language to refer to a marijuana cigarette, which contains cannabis and is subject to legal and health considerations varying by jurisdiction.