CH 9 - pt 2 Types of Synovial Joints -

Introduction to Synovial Joints

  • Synovial joints are classified as diarthrotic joints, which are characterized by a space between articulating bones filled with synovial fluid.
  • The structural classification of these joints indicates they are all freely movable.

Types of Synovial Joints

  • Different types of synovial joints are based on their movement and how articulating condyles fit together.

Hinge Joint

  • Description: A hinge joint functions similarly to a door hinge.
  • Movement: Allows for two primary movements:
    • Flexion: Decreasing the angle at the joint.
    • Extension: Increasing the angle at the joint.
  • Examples of hinge joints include:
    • Elbow joint.
    • Joints between phalanges (finger joints).
    • Knee joint, which is primarily a hinge joint but has some unique movements.
    • Joint between the occipital bone and atlas (allows "yes" movement).
  • Hyperextension: Some individuals can hyperextend their arms, going beyond 180 degrees due to a unique fit of the condyles.

Ball and Socket Joint

  • Description: A synovial diarthrotic joint that allows extensive mobility.
  • Examples: Shoulder and hip joints.
  • Movements possible:
    • Flexion: Humerus moves forward.
    • Extension: Humerus returns to neutral position (straight down).
    • Hyperextension: Humerus extends beyond the neutral position.
    • Abduction: Moving the humerus laterally away from the body.
    • Adduction: Bringing the humerus back towards the body.
    • Rotation: Twisting the axis of the humerus inside the joint.
    • Circumduction: A circular motion that combines flexion, extension, abduction, and adduction; important in actions like throwing.
  • Movement at the hip joint is similar but generally more limited due to the deeper socket (acetabulum) compared to the shoulder (glenoid fossa).

Gliding Joint (Plane Joint)

  • Description: Comprises two flat surfaces that glide over each other.
  • Examples include:
    • Joints between carpal bones.
    • Joints between tarsal bones.
    • Joint between the clavicle and the manubrium of the sternum.

Pivot Joint

  • Description: Allows rotation around a single axis.
  • Examples:
    • Joint between the first (C1, atlas) and second cervical vertebra (C2, axis), allowing rotation to signify "no".
    • Joint between the proximal radius and ulna, allowing circumstantial movements of pronation and supination.
  • Movements defined:
    • Supination: Turning the palm up (like holding a cup of soup).
    • Pronation: Turning the palm down (hands flat on the table).

Ellipsoid Joint (Condyloid Joint)

  • Description: An oval condyle fits into an elliptical cavity of another bone.
  • Examples include:
    • Joint between metacarpals and proximal phalanges.
    • Joint between the radius and scaphoid carpal bone.
  • Movements allowed:
    • Flexion and extension.
    • Abduction and adduction.

Saddle Joint

  • Description: Structurally resembles a saddle, allowing movement in two planes.
  • Example: The joint at the thumb between the trapezium carpal and first metacarpal.
  • Movements:
    • Flexion and extension.
    • Abduction and adduction.

Understanding Joint Movements

  • Understanding joint movement is crucial for grasping muscle function, as muscles are responsible for creating movement at joints:
    • Muscles attached to bones can shorten, causing movement at the joint.
    • Example Muscles depicted:
    • A muscle connecting the pelvis to the femur will cause hip flexion when it contracts.
    • A muscle from the humerus to the radius will cause elbow flexion upon contraction.
  • It is important to recognize the location of muscles and joints to determine their functional outcomes in movement.

Practical Application and Learning

  • Engaging physically in demonstration of joint movements helps reinforce learning and understanding.
  • Use a partner to practice movements such as flexion, extension, abduction, and adduction to gain comfort with joint and muscle interactions.