Joints are the body's connectors, allowing movement and stability. They're classified by function and structure, ranging from immovable skull sutures to freely moving shoulders. Understanding joint types helps us grasp how our bodies move and stay together.

Synovial joints, the most mobile, have unique features like fluid-filled cavities and articular cartilage. These allow smooth motion while cushioning impacts. From hinge joints in fingers to ball-and-socket joints in hips, each type serves a specific purpose in our daily movements.

Joint Classifications and Characteristics

Joint classifications and examples

• Functional classification categorizes joints based on degree of movement
  • Synarthrosis (immovable) joints permit no movement between bones (sutures of the skull, gomphoses between teeth and mandible/maxilla)
  • Amphiarthrosis (slightly movable) joints allow limited movement (pubic symphysis, intervertebral joints)
  • Diarthrosis (freely movable) joints enable a wide range of motion (shoulder joint, knee joint)
• Structural classification categorizes joints based on the type of connective tissue
  • Fibrous joints are connected by fibrous connective tissue without a joint cavity (sutures, gomphoses, syndesmoses like the interosseous membrane between radius and ulna)
  • Cartilaginous joints are united by cartilage without a joint cavity (synchondroses like epiphyseal plates, symphyses such as the pubic symphysis and intervertebral discs)
  • Synovial joints contain a joint cavity filled with synovial fluid and are further classified by shape (plane joints like intercarpal joints, hinge joints such as the elbow and interphalangeal joints, pivot joints like the atlantoaxial joint, condyloid joints such as metacarpophalangeal joints, saddle joints like the carpometacarpal joint of the thumb, ball-and-socket joints such as the hip and shoulder)

Characteristics of joint types

• Synarthroses are immovable joints that provide stability and protection to the body
  • Permit no movement between the articulating bones
  • Examples include the sutures of the skull and gomphoses between teeth and jawbones
• Amphiarthroses are slightly movable joints that allow limited movement while providing stability
  • Enable some flexibility in the joint
  • Examples include the pubic symphysis and intervertebral joints
• Diarthroses are freely movable joints that allow a wide range of motion
  • Contain a joint cavity filled with synovial fluid for lubrication
  • Have articular cartilage covering the ends of the bones to reduce friction
  • Examples include the shoulder joint and knee joint

Features of joint structures

• Fibrous joints are connected by fibrous connective tissue without a joint cavity
  • Collagen fibers directly unite the bones
  • Examples include sutures between skull bones, gomphoses anchoring teeth in sockets, and syndesmoses like the interosseous membrane between the radius and ulna
• Cartilaginous joints are connected by cartilage without a joint cavity
  • Hyaline cartilage or fibrocartilage holds the bones together
  • Examples include synchondroses (growth plates) and symphyses like the pubic symphysis and intervertebral discs
• Synovial joints have unique structural features that enable free movement
  • Articular capsule surrounds the joint creating a joint cavity
  • Synovial fluid fills the joint cavity to lubricate the joint
  • Articular cartilage covers the ends of the bones to minimize friction
  • Ligaments reinforce the joint to provide stability
  • Bursae and fat pads cushion the joint to prevent friction
  • Examples include plane (intercarpal), hinge (elbow), pivot (atlantoaxial), condyloid (metacarpophalangeal), saddle (carpometacarpal of thumb), and ball-and-socket (hip, shoulder) joints

Joint Function and Mechanics

• Range of motion refers to the extent of movement possible at a joint
• Joint stability is influenced by the shape of articulating surfaces and supporting structures
• Articulating surfaces are the areas where bones come into contact within a joint
• Joint biomechanics studies the mechanical forces acting on and within joints during movement