Joints

Joints

1. Structural Classification

   • Fibrous
     • Suture
       • Immobile, wavy bones interlock and are filled with short connective tissue
       • Ex: skull
     • Gomphoses
       • Immobile; Peg-in-socket joint; Joined by periodontal ligament
       • Ex: articulation of tooth with alveolar socket
     • Syndesmoses
       • Slightly mobile Bones are connected by a ligament or a band of long fibers
       • Ex: tibia and fibula(distally)
   • Cartilaginous
     • Synchondroses
       • Immobile; Unites bones with hyaline cartilage
       • Ex: joint between costal cartilage of first rib and manubrium
     • Symphyses
       • Immoble; Bones connected with fibrocartilage; Acts as shock absorber
       • Ex: pubic bone or pubic symphyses of pelvis
   • Synovial
     • Structure
       • Articular cartilage
         • Spongy cushions which absorb compression and prevent bone ends from being crushed
       • Joint cavity
         • Space which contains synovial fluid
       • Articular capsule
         • Consists of two layers; Outside layer is tough fibrous capsule made of irregular connective tissue; Inner layer synovial membrane made of loose connective tissue
       • Synovial fluid
         • Occupies free spaces in joint cavities; Has viscous egg-white consistency; Provides slip between bones to reduce friction between cartilage
       • Reinforcing ligaments
         • capsular or intrinsic ligaments, thickened parts of the fibrous capsule
     • Types
       • Plane Joints
         • Flat articular surfaces which only allow gliding movements and don’t rotate
         • Ex: joint between vertebral articular processes
       • Hinge Joints
         • Cylindrical projection of bone connects to a trough-shaped surface of another bone; Only movements allowed and extension and flexion
         • Ex: joint between ulna and humerus
       • Pivot Joints
         • Round end of one bone connects to ring made of another bone; Only movement is rotation around its long axis
         • Ex: joint between axis and atlas
       • Condyloid Joints
         • Ovular articular surface of one bone connects to a complementary depression of another one; Permits angular motion
         • Ex: joint between metacarpal and phalanges
       • Saddle Joints
         • Both bones concave and convex and are complementary to one another in order to fit together like a puzzle; Resemble shape of saddle; Allows greater freedom to move
         • Ex: carpometacarpal joint of thumb
       • Ball-and-Socket Joints
         • One bone with spherical head fits into another bone with depressed cup-like shape Most freely moving joints
         • Ex: femur and pelvis joint

2. Functional Classification

   • Synarthroses
     • No movement Sutures(fibrous), gomphosis(fibrous), synchondrosis(cartilaginous)
     • Ex: skull
   • Amphiarthroses
     • Slight movement; Syndesmosis(fibrous), symphysis(cartilaginous)
     • Ex: pubic symphysis
   • Diarthroses
     • Freely movable; Synovial joints
       • Nonaxial
         • Slipping movements; No axis
         • Ex: waving hand
       • Uniaxial
         • Movement in one direction; One plane
         • Ex: fingers
       • Biaxial
         • Movement in two directions; Two planes
         • Ex: femur and tibia
       • Multiaxial
         • Movement in all directions; All three planes
         • Ex: hip bone and femur
       • Gliding
         • One bone slips or glides over another
         • Ex: intercarpal and intertarsal joints
       • Angular Movements
         • Flexion
           • Decreases angle of joint; Brings articulating bones closer; Along sagittal plane
           • Ex: bending knee towards back
         • Extension
           • Opposite of flexion; Increases angle between articulating bones; Along sagittal plane
           • Ex: bringing leg straight upwards
         • Dorsiflexion/ Plantar Flexion
           • Dorsiflexion is bringing foot upwards Plantar flexion is bringing foot downwards
         • Circumduction
           • Moving a limb in a cone shape; Distal end of limb makes a circle while the joint is stationary
           • Ex: drawing circles with arms
         • Abduction
           • Movement of limb away from median plane of body
           • Ex: raising arm laterally
         • Adduction
           • Movement of limb closer to median plane of body
           • Ex: moving digits toward midline of hand
         • Rotation
           • Turning bone around its long axis
           • Ex: medial rotation of the thigh