The terms dislocation and subluxation refer to the displacement from their normal position of bones that form a joint. These displacements most often result from injury, causing adjoining bones to no longer align with each other. A partial or incomplete dislocation is called a subluxation.

In a healthy joint, the bones are held together with tough, fibrous bands called ligaments, attached to each bone. Surrounding the joint is a fibrous sac called the articular capsule or joint capsule. The ligaments and joint capsule permit movement within a normal range for each joint. In dislocation, one of the bones making up the joint is forced out of its natural alignment by excessive stretching and tearing of the ligaments and capsule. Muscles and tendons surrounding the joint are usually stretched and injured to some degree.

A violent movement at the joint that exceeds normal limits usually...