Articulations: Anatomy and Clinical Overview

General Features of Joints

  • Articulations (Joints): Meeting place of two or more bones.

  • Range of Motion (ROM): Normal extent of mobility for a specific joint movement.

  • Degrees of Freedom (DOF): Number of axes at which movement in a joint occurs.

  • Stability vs. Mobility: More mobile joints are more prone to injury.

    • Example: Shoulder joint is highly mobile but less stable (susceptible to dislocation).

    • Example: Hip joint is more stable but less mobile.

Classification of Joints

  • Fibrous Joints (Synarthrosis - immovable/Amphiarthrosis - slight movement):

    • Suture: Coronal, lambdoid, sagittal; connect skull bones; no movement.

    • Syndesmosis: Distal tibiofibular; tibia and fibula; slight "give" movement.

    • Gomphosis: Dentoalveolar; tooth and alveolar process; no movement.

  • Cartilaginous Joints (Synarthrosis/Amphiarthrosis):

    • Synchondrosis: Epiphyseal plate; diaphysis and epiphysis of long bones; no movement; converts to synostosis.

    • Symphysis: Intervertebral, symphysis pubis; joined by fibrocartilage pads; slight movement.

  • Synovial Joints (Diarthrosis - free movement): Have a joint cavity with synovial fluid.

    • Uniaxial: E.g., elbow (hinge), atlantoaxial (pivot); 11 axis, 11 DOF.

    • Biaxial: E.g., wrist (condyloid), first carpometacarpal (saddle); 22 axes, 22 DOF.

    • Triaxial (Multiaxial): E.g., shoulder (ball-and-socket); 33 DOF.

    • Nonaxial: E.g., sternocostal (gliding); slight movements in many directions.

Joint Movements

  • Sagittal Plane Movements:

    • Flexion: Raises limbs forward.

    • Extension: Moves limbs backward.

    • Dorsiflexion: Ankle movement (foot upwards).

    • Plantarflexion: Ankle movement (foot downwards).

  • Frontal Plane Movements:

    • Abduction: Movement away from the midline.

    • Adduction: Movement towards the midline.

  • Both Sagittal and Frontal Planes:

    • Circumduction: Combination of movements in a cone-like shape.

  • Longitudinal Axis Movements:

    • Rotation: Head, spine intervertebral discs, ball-and-socket joints.

  • Special Movements:

    • Supination/Pronation: At radioulnar joints.

    • Opposition: Thumb touches fingers.

    • Inversion/Eversion: Intertarsal joints.

    • Elevation/Depression: Upward/downward movement.

    • Protraction/Retraction: Jaw joint movement.

Types of Fibrous Joints (Details)

  • Sutures: Connect skull bones; immovable.

    • Fontanels: Incompletely-ossified areas in infant skulls; ossify by age 22.

  • Syndesmoses: Bones connected by interosseous ligament; slight shift movement.

  • Gomphosis: Teeth in sockets; periodontal ligaments; generally immovable.

Types of Cartilaginous Joints (Details)

  • Synchondroses: Hyaline cartilage connects bones (e.g., epiphyseal plates).

  • Symphyses: Fibrocartilage discs unite bones; allows slight movement (e.g., pubic symphysis, intervertebral).

Synovial Joints (Details)

  • General Features: Joint cavity with synovial fluid; freely movable; most common in appendicular skeleton.

  • Bursitis: Inflammation of a bursa (fluid-filled sac) due to overuse or injury.

Selected Articulations

  • Temporomandibular Joint (TMJ): Combined hinge/gliding joint; mandibular condyle with temporal bone.

  • Intervertebral Joints:

    • Symphysis joints between bodies (fibrocartilage discs).

    • Gliding joints between facets.

  • C1 (Atlas) / C2 (Axis): Double-condyloid joint; allows extended head ROM; most mobile intervertebral articulation.

  • Shoulder Joint: Most freely movable; triaxial ball-and-socket; stabilized by rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis).

  • Shoulder Girdle:

    • Sternoclavicular (gliding).

    • Acromioclavicular (gliding).

    • Scapulothoracic (gliding).

  • Elbow Joint:

    • Humeroulnar: Hinge joint; flexion/extension.

    • Humeroradial: Capitulum of humerus with radius head.

    • Proximal Radioulnar: Pivot joint; pronation/supination.

  • Hip Joint: Triaxial ball-and-socket; femoral head in acetabulum; acetabular labrum deepens socket.

  • Knee Joint: Largest joint; "modified hinge"; little intrinsic stability; supported by menisci and ligaments.

    • ACL Tears: Sprain/tear of anterior cruciate ligament due to injury or sudden movement; often requires surgical reconstruction.

Clinical Considerations

  • Temporomandibular Disorder (TMJ Syndrome): Painful condition affecting TMJ due to misalignment, arthritis, or trauma. Managed with pain relievers, mouth guards, PT.

  • Post-CVA Shoulder Subluxation: Partial dislocation of shoulder due to loss of rotator cuff tone from stroke. Treated with hemi-sling.

  • Developmental Dysplasia of the Hip: Subluxation/dislocation of infant hip joint. Treated with manipulation and positioning harness.

  • Osteoarthritis: Chronic, degenerative joint disease; pain, stiffness, swelling. Managed by symptom control and improving ROM/flexibility.

  • Rheumatoid Arthritis: Autoimmune disease causing chronic joint inflammation; warm, swollen joints, stiffness. Treated with NSAIDs, corticosteroids, DMARDs.

  • Gout: Deposition of urate crystals in joints due to uric acid buildup; intense joint pain and inflammation. Treated with medications to block uric acid or increase excretion.

  • Nursemaid's Elbow: Separation of humeroradial joint in children; radial head slips. Treated by reduction.