Joints are classified according to the amount of movement they permit. Joint classifications are as follows (Fig. 1):
Bones of the skull are an example of an immovable joint. Immovable joints are characterized by the bones being in close contact with each other and little or no movement occurring between the bones.
Slightly movable (amphiarthroses)
In slightly movable joints, the bones are held together by broad flattened disks of cartilage and ligaments (e.g., vertebrae and symphysis pubis).
Freely movable (diarthroses) Most joints in the body are freely movable joints. The joint consists of the joint capsule, articular cartilage, synovial membrane, and synovial (joint) cavity. There are six classifications of freely movable joints: ball-insocket, condyloid, gliding, hinge, pivot, and saddle joints (Fig. 2). 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, the injury is called a sprain. When bones are out of place, it is called a dislocation. 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 (Table 1).
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 motion decreases or increases the angle between two adjoining bones. The more common types of angular motion are as follows:
Other Types of Movement
Table 1.—Synovial Joints.
TEMPORAL MANDIBULAR JOINT
The right and left temporal mandibular joints (TMJs) are formed by the articulation of the temporal bone and the mandible. This is where TMJs connect with the rest of the skull. Figure 3 illustrates the TMJ.
The mandible is joined to the cranium by ligaments of the temporal mandibular joint. The TMJ consists of three bony parts:
|David L. Heiserman, Editor||
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Revised: June 06, 2015