Articulations

Articulations and Joints Introduction

• The human body contains 206 bones, with all but one articulating with at least one other bone.

• Understanding how joints move is crucial:

  • How many joints move very much?

  • How many joints move at all?

• Key concepts to consider in joint classification: strength and movement.

I. Classification of Joints by Structure

• Classification of joints can be outlined into three primary categories:
  I. Fibrous Joints
  II. Cartilaginous Joints
  III. Synovial Joints

I. A. Fibrous Joints

• Characteristics:

  • Typically exhibit no movement.

  • An example includes skull bone sutures.

  • Limited movement can occur in structures like tooth sockets.

  • Also includes ligaments connecting radius and ulna.

  • Structure defined by dense connective tissue (CT) with no joint cavity.

  • Strong yet allow little to no movement.

I. B. Cartilaginous Joints

• Characteristics:

  • Include epiphyseal cartilages in growing bones.

  • Example includes joints between ribs and costal cartilages.

  • Symphyses, such as pubic, mental, and intervertebral disks are also included.

  • Composed of either hyaline or fibrocartilage.

  • Allow little to no movement.

I. C. Synovial Joints

• General Structure:

  • Mostly found in appendicular skeleton.

  • Main Components:

  • Synovial Fluid:

    • Fills joint cavity.

    • Acts as lubricant, shock absorber, and transport medium for nutrients and wastes.

  • Joint Capsule:

    • Defines an avascular internal space.

    • Composed of a fibrous capsule (dense irregular CT outer layer) and synovial membrane that produces synovial fluid.

  • Articular Cartilages:

    • Provide more mobility but render the joint weaker.

• The synovial joint may also contain ligaments, tendons, and bursae or tendon sheaths for additional support.

II. Describing the Motion of Joints

II. A. Types of Joint Motion

1. Gliding Motion:

   • Involves little actual movement characterized by two bones sliding on each other’s surfaces.

   • Examples include carpals, tarsals, and the connection between the clavicle and sternum.

2. Angular Motion:

   • Involves increasing or decreasing the angle between two bones at a joint.

   • Examples:

     • Flexion/Extension:

     • Decreases or increases the angle in the anterior/posterior (sagittal) plane, with hyperextension as a note.

     • Abduction/Adduction:

     • Movement away from or towards the axis of the body, with circumduction being a circular movement around an axis.

3. Circular Motions:

   • Include movements that pivot around an axis, such as:

     • Left/Right rotation.

     • Medial/Lateral rotation.

     • Pronation/Supination.

     • Circumduction, a complex motion composed of a combination of flexion, extension, abduction, and adduction.

4. Special Motions:

   • Include unique movements that do not fall under standard categories such as:

     • Retraction

     • Protraction

     • Elevation

     • Depression

     • Opposition

     • Lateral flexion

     • Dorsiflexion (ankle flexion)

     • Plantar flexion (ankle extension)

III. Synovial Joint Classification by Type of Movement/Action

• Types of Synovial Joints:

  1. Gliding/Plane Joint

  2. Hinge Joint

  • Angular movement usually occurs along one axis, examples include the elbow, knee, interphalangeal joints, and the ankle.

  1. Pivot Joint

  • Allows rotational movement around an axis, with examples such as the atlas/axis joints and proximal & distal radioulnar joints.

  1. Ellipsoidal Joint

  • Also known as a condylar joint, allowing biaxial movement including angular motion and circumduction, with examples including the radiocarpal joint and metacarpophalangeal joints.

  1. Saddle Joint

  • Similar to ellipsoidal joints allowing all angular motion and circumduction but no rotation. An example includes the 1st carpometacarpal joint.

  1. Ball-and-Socket Joint

  • Allows triaxial movement, enabling all angular and rotational motion, with shoulder and hip joints as prime examples.

IV. The Knee: An Example of a Synovial Joint

• Structure:

  • Composed of various components including:

  • Femur, tibia, fibula

  • Articular cartilage, ligaments (patellar ligament also known as patellar tendon, fibular collateral ligament, and tibial collateral ligament), and menisci (medial and lateral).

  • Specific components identified from various perspectives:

    • Anterior view showing the patella and quadriceps tendon (cut)

    • Sagittal section showing tibiofemoral and patellofemoral joints.

• Key Movements:

  • The knee, classified as a hinge joint, primarily allows flexion and extension, thus demonstrating uniaxial motion.

V. Practical Applications of Joint Classification

• For practical assessments of joint structures and functions:

  • Determine the types of joints involved.

  • Identify the types of motions or actions facilitated by the joint.

  • Example Analysis:

  • Identifying the elbow joint: it is a synovial hinge joint allowing flexion/extension, displaying angular mobility only.