liðið

Liðið, in anatomy, refers to the connection between bones that allows motion. Joints may involve cartilage, ligaments, tendons and a joint capsule that encloses a synovial cavity in many joints. The arrangement of these parts determines how the joint moves and how stable it is.

Joints are traditionally classified by mobility into fibrous joints (immovable or barely movable), cartilaginous joints (slightly movable), and synovial joints (freely movable). Fibrous joints include skull sutures; cartilaginous joints include intervertebral discs; synovial joints include the knee, hip, shoulder and elbow. Synovial joints share key features: articular cartilage on the contacting bones, an articular capsule, a synovial membrane that produces fluid, and reinforcing ligaments. Some joints also include menisci, discs or bursae to improve fit and absorb load.

Within synovial joints, movement is described by planes and axes and includes types such as hinge (elbow), pivot (radius and ulna), ball-and-socket (hip, shoulder), condyloid (wrist), saddle (thumb), and gliding joints (between small hand and foot bones).

Joints enable a balance between mobility and stability, transmit and absorb forces, and rely on muscles for movement as well as proprioception for position sense. Clinical relevance includes conditions such as osteoarthritis, inflammatory arthritis, dislocations, sprains, and injuries to ligaments or menisci, which can reduce range of motion and cause pain.