Classification of Joints

Structural Classification of Joints

There are three structural classifications of joints: fibrous, cartilaginous, and synovial.

Learning Objectives

Describe the three structural categories of joints

Key Takeaways

Key Points

  • The type
    and characteristics of a given joint determine the degree and type of movement.
  • Structural classification categorizes joints based on the type of
    tissue involved in their formations.
  • There are three structural
    classifications of joints: fibrous, cartilaginous, and synovial.
  • Of the three types of fibrous joints, syndesmoses are the most movable.
  • Cartilaginous
    joints allow more movement than fibrous joints
    but less than synovial joints.
  • Synovial joints ( diarthroses ) are the most movable joints of the body and contain synovial fluid.

Key Terms

  • periosteum: A membrane that covers the outer surface of all bones.
  • manubrium: The broad upper part of the sternum.
  • synovial fluid: A viscous fluid found in the cavities of synovial
    joints that reduces friction between the articular cartilage during movement.

A joint, also known as an articulation or articular surface, is a connection that occurs between bones in the skeletal system. Joints provide the means for movement. The type and characteristics of a given joint determines its degree and type of movement. Joints can be classified based on structure and function.

Structural classification of joints categorizes them based on the type of tissue involved in formation. There are three structural classifications of joints: fibrous, cartilaginous, and synovial.

Fibrous Joints

Fibrous joints are connected by dense, tough connective tissue that is rich in collagen fibers. These fixed or immovable joints are typically interlocked with irregular edges. There are three types of fibrous joints.

Sutures are the types of joint found in the cranium (skull). The bones are connected by Sharpey’s fibres. The nature of cranial sutures allows for some movement in the fetus. However, they become mostly immovable as the individual ages, although very slight movement allows some necessary cranial elasticity. These rigid joints are referred to as synarthrodial.

Syndesmoses are found between long bones of the body, such as the radio-ulnar and tibio-fibular joints. These moveable fibrous joints are also termed amphiarthrodial. They have a lesser range of movement than synovial joints.

Gomphosis is a type of joint found at the articulation between teeth and the sockets of the maxilla or mandible (dental-alveolar joint). The fibrous tissue that connects the tooth and socket is called the periodontal ligament.

Image demonstrating the three types of fibrous joints and delineating structures including suture line, suture, dense fibrous connective tissue, ulna, radius, syndesmosis, antebrachial interosseous membrane, socket, gomphosis, root of tooth, and periodontal ligament.

Fibrous joints: Image demonstrating the three types of fibrous joints. (a) Sutures (b) Syndesmosis  (c) Gomphosis.

Cartilaginous Joints

Cartilaginous joints are connected by fibrocartilage or hyaline cartilage. They allow more movement than fibrous joints but less than that of synovial joints. These types of joints are further subdivided into primary (synchondroses) and secondary (symphyses) cartilaginous joints. The epiphyseal (growth) plates are examples of synchondroses. Symphyses are found between the manubrium and sternum (manubriosternal joint), intervertebral discs, and the pubic symphysis.

Image demonstration a synchondrosis joint (a) and a symphysis joint.

Cartilaginous Joints: Image demonstrates a synchondrosis joint with epiphyseal plate (temporary hyaline cartilage joint) indicated (a) and a symphysis joint (b).

This figure shows a synovial joint. The cavity between two bones contains the synovial fluid which lubricates the two joints.

Synovial Joint: This diagram of a synovial joint delineates the articular cartilage, articular capsule, bone, synovial membrane, and joint cavity containing synovial fluid.

Synovial Joints

This is the most common and movable joint type in the body. These joints (also called diarthroses) have a synovial cavity. Their bones are connected by dense irregular connective tissue that forms an articular capsule surrounding the bones’ articulating surfaces.

A synovial joint connects bones with a fibrous joint capsule that is continuous with the bones’ periosteum. This joint capsule constitutes the outer boundary of a synovial cavity and surrounds the bones’ articulating surfaces.

Synovial cavities are filled with synovial fluid. The knees and elbows are examples of synovial joints.

Functional Classification of Joints

Functional classification of joints is based on the type and degree of movement permitted.

Learning Objectives

Describe the three functional categories of joints

Key Takeaways

Key Points

  • Synarthrosis joints are immobile or have limited mobility and include fibrous joints.
  • Amphiarthrosis joints allow a small amount of mobility and include cartilaginous joints.
  • Diarthrosis joints are the freely movable synovial joints.
  • Synovial joints can also be classified as nonaxial, monoaxial, biaxial, and multiaxial.
  • The various movements permitted by synovial joints are abduction, adduction, extension, flexion, and rotation.

Key Terms

  • fibrous joints: Fixed or immobile joints that are connected by dense, tough connective tissue that
    is rich in collagen fibers.
  • cartilaginous joints: Joints connected by fibrocartilage or hyaline cartilage. They allow more movement than fibrous joints but less than synovial joints.
  • gomphosis joints: Joints of very limited mobility. These are found at the articulation
    between teeth and the sockets of maxilla or mandible (dental-alveolar joint).

Joints or articulations (connections between bones) can be classified in a number of ways. The primary classifications are structural and functional. Functional classification is based on the type and degree of movement permitted.

Image of a skeleton and schematics of the different classes of synovial joints.Terms include pivot joint (between C1 and C2 vertebrae), ball and socket joint (hip joint), hinge joint (elbow), condyloid joint (between radius and carpal bones of wrist), plane joint (between tarsal bones), saddle joint (between trapezium carpal bone and first metacarpal bone).

Types of Synovial Joints.jpg: Image of a skeleton and skematics of the different classes of synovial joints.

Three Categories of Functional Joints

  • Synarthrosis: These types of joints are immobile or allow limited mobility. This category includes fibrous joints such as suture joints (found in the cranium) and gomphosis joints (found between teeth and sockets of the maxilla and mandible).
  • Amphiarthrosis: These joints allow a small amount of mobility. Most joints in this category
    include cartilaginous joints such as those found between vertebrae and the pubic symphysis.
  • Diarthrosis: These are the freely-movable synovial joints. Synovial joints are further classified based on the different types of movement they provide, including:
    • Plane joint
    • Ball and socket joint
    • Hinge joint
    • Pivot joint
    • Condyloid joint
    • Saddle joint

Movement of Synovial Joints

Joints can also be classified by the number of axes of movement they permit:

  • Nonaxial (gliding): Found between the proximal ends of the ulna and radius.
  • Monoaxial (uniaxial): Movement occurs in one plane. An example is the elbow joint.
  • Biaxial: Movement can occur in two planes. An example is the wrist.
  • Multiaxial: Includes the ball and socket joints. An example is the hip joint.

The movements possible with synovial joints are:

  • Abduction: movement away from the body’s midline
  • Adduction: movement toward the body’s midline
  • Extension: straightening limbs at a joint
  • Flexion: bending the limbs at a joint
  • Rotation: a circular movement around a fixed point