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JOINTS


Learning Objectives

  1. Identify joint classifications.
  2. Identify joint movements for the key joints in the body. Wherever two or more bones meet a joint is formed. A joint binds various parts of the skeletal system together and enables body parts to move in response to skeletal muscle contractions.

JOINT CLASSIFICATIONS

Joints are classified according to the amount of movement they permit. Joint classifications are as follows (Fig. 1):

Immovable (synarthroses)

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).

Figure 1.—Joint Classifications

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.

Figure 2.—Types of synovial joints. Uniaxial: A, hinge, and B, pivot. Biaxial: C, saddle, and D, condyloid. Multiaxial: E, ball and socket, and F, gliding.

TYPES OF JOINT MOVEMENTS

Joint movements are generally divided into four types: gliding, angular, rotation, and circumduction (Table 1).

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: A movement in which the bone moves around a central point without being displaced, such as turning the head from side to side.
  • Circumduction: The movement of the hips and shoulders.

Other Types of Movement

  • Supination: Turning upward, as in placing the palm of the hand up.
  • Pronation: Turning downward, as in placing the palm of the hand down or placing sole of the foot to the outside.
  • Inversion: Turning inward, as in turning the sole of the foot inward.
  • Eversion: Turning outward, as in turning the sole of the foot outward.


Table 1.—Synovial Joints.

Image reprinted  from: Thibedeau, G. A., & Patton, K. T. (2006). Anatomy & Physiology (6th ed.). St. Louis: Elsevier Health Sciences.

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:

  • Glenoid fossa: Oval depression in the temporal bone that articulates with the mandibular condyle.
  • Articular eminence: Ramp-shaped segment of the temporal bone located anterior to the glenoid fossa.
  • Condyle: The knuckle-shaped portion of the mandibular ramus found on the end of the condyloid process. It is positioned underneath the glenoid fossa and makes up the hinge joint of the TMJ.

Figure 3.—Temporal Mandibular Joint


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David L. Heiserman, Editor

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Revised: June 06, 2015