TYPES OF JOINT MOVEMENTS

� Freely movable. Most joints in the body are freely movable joints. The joint consists of the joint capsule, articular cartilage, synovial membrane, and synovial (joint) cavity (fig. 1-26). There are six classifications of freely movable joints: ball-in-socket, condyloid, gliding, hinge, pivot, and saddle joints (fig. 1-27). These joints have much more complex structures than the immovable and slightly movable joints. The ends of the bones in this type of joint are covered with a smooth layer of cartilage. The whole joint is enclosed in a watertight sac or membrane containing a small amount of lubricating fluid. This lubrication enables the joint to work with little friction. Ligaments (cords or sheets of connective tissue) reach across the joints from one bone to another and keep the bone stable. When ligaments are torn, we call the injury a sprain; when bones are out of place, we refer to this as a dislocation; and when bones are chipped or broken, the injury is called a fracture. TYPES OF JOINT MOVEMENTS Joint movements are generally divided into four types: gliding, angular, rotation, and circumduction. Gliding Gliding is the simplest type of motion. It is one surface moving over another without any rotary or angular motion. This motion exists between two adjacent surfaces. Angular Angular motion decreases or increases the angle between two adjoining bones. The more common types of angular motion are as follows: � Flexion—bending the arm or leg. � Extension—straightening or unbending, as in straightening the forearm, leg, or fingers. � Abduction—moving an extremity away from the body. � Adduction—bringing an extremity toward the body. Rotation Rotation is a movement in which the bone moves around a central point without being displaced, such as turning the head from side to side. 1-16 SYNOVIAL MEMBRANE SYNOVIAL (JOINT) CAVITY JOINT CAPSULE ARTICULAR CARTILAGE FREELY MOVABLE JOINT SYMPHYSIS PUBIS CORONAL SUTURE INTERNASAL SUTURE FIBROUS SUTURE IMMOVABLE JOINT SLIGHTLY MOVABLE JOINT HM3F0126 Figure 1-26.—Example of immovable, slightly movable, and freely movable joints.