Joints and Articulations

An articulation, or joint, is the point where two or more bones meet. Joints hold the skeleton together and, in most cases, allow movement. They vary widely in structure and in how freely they move. Some, such as the sutures of the skull, are essentially fixed; others, such as the joints between the bones of the spine, permit only limited movement; and the most familiar joints, including those of the limbs, are freely movable synovial joints. In a synovial joint, the bone ends are capped with smooth cartilage and enclosed in a capsule containing lubricating synovial fluid, which reduces friction during movement.

Different synovial joints permit different motions. The knee and the elbow are hinge joints that mainly bend and straighten in one plane, while the shoulder and hip are ball-and-socket joints that allow movement in many directions. The hand and wrist contain numerous small joints that together provide the fine, varied movements used for grasping and manipulation. Ligaments connect bone to bone and stabilise joints, while tendons attach muscles to bones so that muscle contraction produces movement.

Joints are subject to injury and disease. A dislocation occurs when bones are forced out of their normal alignment, and arthritis refers to inflammation of joints, which can cause pain and stiffness. Conditions such as osteoporosis weaken bone and raise the risk of fracture near joints, and back pain is sometimes described as lumbago. Arthroscopy, a procedure using a small camera inserted into a joint, allows surgeons to examine and treat joint problems through tiny incisions.

Frequently asked questions

What is a synovial joint?

A synovial joint is a freely movable joint where cartilage-capped bone ends meet within a capsule of lubricating synovial fluid, as in the knee and shoulder.

What is the difference between a hinge and a ball-and-socket joint?

A hinge joint, like the elbow or knee, moves mainly in one plane, while a ball-and-socket joint, like the shoulder or hip, allows movement in many directions.

What is arthroscopy?

Arthroscopy is a procedure in which a small camera is inserted into a joint through a tiny incision, letting surgeons examine and treat the joint with minimal disruption.