Synovial Joint Shapes and Movements

Synovial Joint Shape and Movement

• Condylar (ellipsoid) joints: Allow movement in two planes (biaxial)

  • Types of movement: Abduction/adduction, flexion/extension, circumduction
  • Examples: Radiocarpal joint, metacarpophalangeal joint

• Saddle joints: Allow movement in two planes (biaxial)

  • Types of movement: Abduction/adduction, flexion/extension, circumduction, opposition
  • Examples: Thumb (1st carpophalangeal joint)

• Ball-and-socket joints: Allow movement in all axes (multiaxial)

  • Types of movement: Abduction/adduction, flexion/extension, rotation, circumduction
  • Examples: Shoulder and hip joints

Shoulder (Glenohumeral) Joint

• Most freely movable joint but lacks stability
• Articular capsule is thin and loose
• Important ligaments: Glenohumeral ligament, coracohumeral ligament, coracoacromial ligament

Bursae and Tendon Sheaths

• Bursa: Membrane-bound pocket filled with synovial fluid

  • Found where tendons or ligaments rub against bone or other tissue
  • Reduces friction and absorbs shock

• Tendon Sheath: A bursa that extends along a tendon

Elbow Joint

• Hinge joint: Articulation of the humero-ulnar joint with the trochlear notch of the ulna allows only flexion and extension
• Radio-ulnar Joints: Proximal and distal joints allow rotational movements of supination and pronation
• Important ligaments: Ulnar collateral ligament, radial collateral ligament, annular ligament

Hip Joint

• Ball-and-socket structure
• Movements occur in all axes but are limited by ligaments and the acetabulum
• Head of femur articulates with the acetabulum
• Stability primarily from acetabulum and capsular ligaments:
  • Iliofemoral
  • Pubofemoral
  • Ischiofemoral
  • Ligament of the head of femur

Knee Joint

• Acts primarily as a hinge joint
• Two fibrocartilage menisci occur within the joint cavity
• Femoropatellar joint: Shares joint cavity, allows patella to glide across the distal femur

Knee Joint Ligaments

• Extracapsular: Fibular and tibial collateral ligament
• Intracapsular ligaments: Cruciate ligaments (cross each other like an “X”)
  • Anterior cruciate ligament: Prevents anterior sliding of the tibia
  • Posterior cruciate ligament: Prevents forward sliding of the femur or backward displacement of the tibia

Synovial Joints Overview

• Most movable type of joint (diarthroses)
• Components:
  • Fluid-filled joint cavity
  • Articular cartilage
  • Articular capsule (fibrous layer and synovial membrane)
  • Synovial fluid
  • Reinforcing ligaments
  • Some synovial joints contain an articular disc

Synovial Joint Movements

• Gliding: One bone glides across the surface of another, no change in angle between joints
• Angular movement: Changes angle between bones:
  • Flexion and extension: Bending and straightening
  • Abduction and adduction: Moving closer or farther away from the trunk
  • Circumduction: Combination of two movements that look like making a cone
• Rotation: Movement around a bone’s long axis

Synovial Joint Shapes

• Plane joint: Articular surfaces are flat planes

  • Types of movement: Gliding
  • Examples: Intercarpal, intertarsal, Acromioclavicular

• Hinge joints: Uniaxial, allow angular movement in one plane

  • Types of movement: Flexion/extension
  • Examples: Elbow, Knee, Ankle, Interphalangeal

• Pivot joints: Uniaxial, allow only rotation of bones around their long axis

  • Types of movement: Rotation
  • Examples: Atlantoaxial, Radioulnar

Joint Classification

• Functional classification based on movement:

  • Synarthroses: Immovable (common in axial skeleton)
  • Amphiarthroses: Slightly movable (common in axial skeleton)
  • Diarthroses: Freely movable (common in appendicular skeleton)

• Structural classification based on material binding bones:

  • Fibrous: Bones connected by fibrous connective tissue
  • Cartilaginous: Bones connected by cartilage
  • Synovial: Bones connected by synovial membrane

Fibrous Joints

• Three types:
  • Sutures: Short fibers between bones, not movable (Synarthroses)
    • Examples: Skull sutures
  • Syndesmosis: Long fibers between bones, slightly movable (Amphiarthroses)
    • Examples: Between radius and ulna or tibia and fibula
  • Gomphosis: Periodontal ligament between bones, not movable (Synarthroses)
    • Examples: Teeth roots in jaws

Cartilaginous Joints

• Two types
  • Synchondroses: Hyalin cartilage between bones, not movable (Synarthroses)
    • Examples: Costochondral joints, epiphyseal plates in long bones
  • Symphyses: Fibrocartilage between bones, slightly movable (Amphiarthroses)
    • Examples: Intervertebral discs, symphysis pubis