Joint Classifications, Movements, and Pathologies

Joint Classification and Synovial Joint Dynamics

  • Structural Classifications:

    • Bony: Synostosis.

    • Fibrous: Sutures, Syndesmosis, Gomphosis.

    • Cartilaginous: Synchondrosis, Symphysis.

    • Synovial: Plane, Hinge, Pivot, Condylar, Saddle, Ball-and-socket (diarthrotic, fluid-filled cavity).

  • Stability Factors:

    • Muscle tone: Most important factor, keeping tendons taut across joints.

    • Ligament number and location: Limited role.

    • Shape of articular surface: Minor role.

  • Mechanics & Range of Motion:

    • Muscle contraction pulls insertion (movable bone attachment) toward origin (immovable bone attachment).

    • Motion ranges: Nonaxial (slipping), Uniaxial (one plane), Biaxial (two planes), Multiaxial (three planes).

Synovial Joint Movements

  • Gliding: Flat bone surfaces slide past each other (e.g., intercarpal, intertarsal, intervertebral articular processes).

  • Angular Movements:

    • Flexion / Extension / Hyperextension: Decreases joint angle / Increases joint angle / Movement beyond anatomical position.

    • Abduction / Adduction: Movement away from / toward midline along frontal plane.

    • Circumduction: Limb moves to describe a cone in space.

  • Rotation: Bone turns around its long axis (Medial toward midline; Lateral away from midline).

  • Special Movements:

    • Supination / Pronation: Palm faces anteriorly (radius and ulna parallel) / Palm faces posteriorly (radius rotates over ulna).

    • Dorsiflexion / Plantar flexion: Bending foot toward shin / Pointing toes downward.

    • Inversion / Eversion: Sole of foot faces medially / Sole faces laterally.

    • Protraction / Retraction: Mandible juts out / Mandible moves back toward neck.

    • Elevation / Depression: Lifting body part superiorly / Lowering body part inferiorly.

    • Opposition / Reposition: Thumb touches fingertips / Thumb returns to anatomical position.

Joint Injuries and Inflammatory Conditions

  • Cartilage Tears: Caused by compression and shear stress; fragments cause joint locking or binding; poor self-repair; managed via arthroscopic surgery.   

    Torn medial meniscus arthroscopy

  • Sprains: Ligaments stretched or torn; poor vascularization leads to slow repair; treated with immobilization, suturing, or grafts.

  • Dislocations (Luxations): Bones forced out of alignment; partial dislocation is termed subluxation; requires reduction.

  • Bursitis & Tendonitis: Inflammation of bursae (from friction/blows) or tendon sheaths (from overuse).

Arthritic Diseases

  • Osteoarthritis (OA):

    • Chronic wear-and-tear degenerative disease affecting half of Americans by age 85 (more women than men).

    • Cartilage breaks down faster than replaced, forming bone spurs (osteophytes) and producing joint crepitus.

  • Rheumatoid Arthritis (RA):

    • Autoimmune chronic inflammatory disease usually arising between ages 40 and 50 (affects 3 times as many women as men).

    • Begins with synovitis, leading to fluid accumulation, abnormal pannus tissue, cartilage erosion, and ankylosis.   

      Hand deformed by rheumatoid arthritis

  • Gouty Arthritis: Deposition of uric acid crystals in joints (most commonly base of great toe); more common in men; untreated cases risk joint immobilization.

  • Lyme Disease: Tick-borne bacterial infection causing joint pain, rash, flu-like symptoms, and foggy thinking; treated with antibiotics.