Joints and Their Classification

Objectives

When you have completed this section, you should be able to

  • explain what joints are, how they are named, and what functions they serve;
  • define arthrology, kinesiology, and biomechanics; and
  • name and describe the three major structural classes and three major functional classes of joints.

Arthrology is the science concerned with the anatomy, function, dysfunction, and treatment of joints. The study of musculoskeletal movement is called kinesiology (kih-NEE-see-OL-oh-jee). This is a subdiscipline of biome-chanics, which deals with a broad range of motions and mechanical processes, including the physics of blood circulation, respiration, and hearing.

Joints such as the shoulder, elbow, and knee are remarkable specimens of biological design—self-lubricating, almost frictionless, and able to bear heavy loads and withstand compression while executing smooth and precise movements (fig. 9.1). Yet, it is equally important that other joints be less movable or even immovable. Such joints are better able to support the body and provide protection for delicate organs. The vertebral column, for example, must provide a combination of support and flexibility; thus its joints are only moderately movable. The immovable joints between the cranial bones afford the best possible protection for the brain and sense organs.

The name of a joint is typically derived from the names of the bones involved. For example, the atlanto-occipital joint is where the occipital condyles meet the atlas, the humero-scapular joint is where the humerus meets the scapula, and the coxal joint is where the femur meets the os coxae.

Joints can be classified according to their relative freedom of movement:

• A diarthrosis1 (DY-ar-THRO-sis) is a freely movable joint such as the elbow.

Slightly Movable Joints Ribs
Figure 9.1 Joint Flexibility. This gymnast demonstrates the flexibility, precision, and weight-bearing capacity of the body's joints.
  • An amphiarthrosis2 (AM-fee-ar-THRO-sis) is a joint that is slightly movable, such as the intervertebral and intercarpal joints.
  • A synarthrosis3 (SIN-ar-THRO-sis) is a joint that is capable of little or no movement, such as a suture of the skull.

Joints are also classified according to the manner in which the adjacent bones are joined. In this system, there are fibrous, cartilaginous, bony, and synovial joints, defined and described in the sections that follow. These two sys-

1 dia = separate, apart + arthr = joint + osis = condition

Saladin: Anatomy & I 9. Joints I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 9 Joints 295

Functional classification

I

Based on relative joint mobility

4

Fibrous Joints Examples

Fibrous joints: Bones held together by collagenous fibers extending from the matrix of one bone into the matrix of the next; no joint cavity Examples: skull sutures teeth in sockets distal radioulnar joints tibiofibular joints

Cartilaginous joints: Bones held together by cartilage; no joint cavity Examples:

epiphyseal plates of long bones costosternal joints pubic symphysis intervertebral discs

Amphiarthroses: Slightly movable joints

Examples:

intervertebral discs

joints between articular processes of cervical to

lumbar vertebrae

costosternal joints (ribs 2-7)

pubic symphysis

distal radioulnar joints

tibiofibular joints

Diarthroses: Freely movable synovial joints

Examples:

shoulder, elbow, carpal joints

hip, knee, tarsal joints

interphalangeal joints

Synarthroses: Joints with little or no movement Examples: skull sutures teeth in sockets epiphyseal plates of long bones first costosternal joint mental symphysis

Figure 9.2 Systems of Classifying the Joints. Left: A structural classification based on how the bones are joined. Right: A functional classification based on relative joint mobility. Connecting lines indicate overlap between the classification systems. For example, synovial joints can be either diarthroses or amphiarthroses, all diarthroses are synovial joints, and amphiarthroses include joints of the synovial, fibrous, and cartilaginous types.

tems of classification overlap. For example, synovial joints may be either diarthroses or amphiarthroses, and amphiarthroses can be any of the three structural types— synovial, fibrous, or cartilaginous (fig. 9.2).

Before You Go On

Answer the following questions to test your understanding of the preceding section:

  1. What is the difference between arthrology and kinesiology?
  2. Describe the two basic ways of classifying joints. What distinctions are looked for in each system?
  3. Explain the distinction between a diarthrosis, amphiarthrosis, and synarthrosis. Give an example of each.

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Responses

  • goytiom luwam
    What are the two systems for classifying joints?
    7 years ago
  • fnan
    What is the difference between arthrology and kinesiology?
    7 years ago
  • Leon
    What are joints and their categories?
    7 years ago
  • Guendalina
    Which joints are important in kinesiology dia?
    6 years ago

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