Chapter 7: Articulations Part 2

Chapter 7: Articulations

Learning Objectives

  • L.O. 7.1: Define anatomical position, range of motion, and degrees of freedom.
  • L.O. 7.2: Identify the types of motion possible at movable joints.
  • L.O. 7.3: Classify joints by structure and function.
  • L.O. 7.4: Relate joint structure to joint function.
  • L.O. 7.5: Predict the effects of various injuries/pathologies on joint function.
  • L.O. 7.6: Defend this proposal: "The knee joint should not be classified as a hinge joint, but rather as a double condyloid joint."

General Features of Joints

  • ARTICULATION (JOINT): The meeting place of two or more bones.
  • RANGE OF MOTION: Refers to the normal extent of mobility for a specific joint movement.
  • DEGREES OF FREEDOM: The number of axes at which movement in a joint occurs.
  • STABILITY VS. MOBILITY: The more mobile a joint is, the more likely it is to sustain injuries.

Classification of Joints

Basis of Joint Classification
  • Joints allow the movement of the skeleton at points of articulation (where two or more bones meet).
  • Classified based on:
    • Structure: Presence or absence of a joint cavity.
    • Function: The functionality or amount of movement in the joint.
Structural Classification

  1. Fibrous: Joints with fibrous tissue, no joint cavity.

    • Types:
      • Sutures: Seams between bones (e.g., skull).
      • Syndesmoses: Bones connected by a ligament with minimal movement.
      • Gomphoses: Peg-in-socket connections found in teeth.

  2. Cartilaginous: Joints connected by cartilage, no cavity present.

    • Types:
      • Synchondroses: Bar of hyaline cartilage connecting bones or parts of bones (e.g., epiphyseal plate).
      • Symphyses: Fibrocartilage discs unite bones, allowing slight movement (e.g., pubic symphysis, joints connecting vertebral bodies).

  3. Synovial: Articulating bones are separated by a fluid-containing cavity (synovial cavity containing synovial fluid).

Functional Classification
  • Synarthroses: Immovable joints, typically found in the axial skeleton.
  • Amphiarthroses: Slightly movable joints, also located in the axial skeleton.
  • Diarthroses: Freely movable joints, found in the limbs.

Fibrous Joints

  • Composed of fibrous tissue, characterized by little to no movement.
  • Types:
    • Sutures: Seams connecting membranous bones of the skull that are immovable.
    • Syndesmoses: Bones connected by interosseous ligaments allowing slight movement.
    • Gomphoses: Connective tissue fibers (periodontal ligaments) articulate teeth with maxilla or mandible; mostly immovable but may show some motion over time.

Cartilaginous Joints

  • Connections made by cartilage.
  • Types:
    • Synchondroses: Hyaline cartilage connects bones; e.g., epiphyseal plates representing developmental history.
    • Symphyses: Fibrocartilage discs unite bones, allowing slight movement; e.g., pubic symphysis, intervertebral joints.

Synovial Joints

Overview
  • Characterized by a joint cavity containing synovial fluid which facilitates movement.
Features
  • Articular Cartilage: Hyaline cartilage covering opposing bone surfaces.
  • Joint (Synovial) Cavity: The space filled with synovial fluid.
  • Articular Capsule: A fibrous capsule with a synovial membrane enhancing joint strength.
  • Synovial Fluid: Acellular fluid that reduces friction and nourishes articular cartilage, containing primarily water and hyaluronic acid.
  • Reinforcing Ligaments: Provide additional stability to joints.

Joints and Their Functionality

Reducing Friction in Joints
  • Bursae: Flattened fibrous sacs filled with synovial fluid to cushion joints.
  • Tendon Sheaths: Elongated bursae that wrap around tendons, providing lubricant during movement.
Factors Influencing Stability of Synovial Joints
  1. Articular surfaces: Minor role, where shallow surfaces are less stable than ball-and-socket designs.
  2. Ligaments: More ligaments typically offer a stronger joint but provide limited stability.
  3. Muscle Tone: Important for stability; tone keeps tendons tense and helps maintain alignment of bones.

Joint Movements

Types of Joint Movements

  1. Flexion/Extension: Occurs in the sagittal plane.

    • Flexion: Raises limbs forward (anterior direction).
    • Extension: Moves limbs backward (posterior direction).
    • Dorsiflexion and Plantarflexion: Specific terms used for ankle movement.

  2. Abduction/Adduction: Primarily occurs in the frontal plane.

    • Abduction: Movement away from the body's midline.
    • Adduction: Movement towards the body's midline.

  3. Circumduction: Involves a cone-like movement combining flexion, extension, abduction, and adduction.

  4. Rotation: Movement around the longitudinal axis of the moving segment.

    • Includes head rotation on the neck, rotation of intervertebral discs, and movements at ball-and-socket joints.

  5. Special Movements: Includes specialized joint movements such as:

    • Inversion/Eversion: Movements specific to intertarsal joints.
    • Elevations/Depressions: Movements upwards or downwards.
    • Protraction/Retration: Jaw movements at the temporomandibular joint.

Types of Fibrous Joints

SUTURES
  • Connect membranous bones of the skull; immovable.
FONTANELS
  • Areas of incompletely-ossified membranes in fetal and infant skulls; ossify by age 2.
SYNDESMOSES
  • Bones connected by interosseous ligaments, allowing slight give/movement.
GOMPHOSIS
  • Connective tissue fibers articulate teeth with sockets; generally immovable but may exhibit movement over time.

Types of Cartilaginous Joints

SYNCHONDROSES
  • Bones are connected by hyaline cartilage.
  • E.g. epiphyseal plates, revealing history of cartilage before bone development.
SYMPHYSES
  • Fibrocartilage discs unite bones and allow slight movement; e.g. pubic symphysis, intervertebral discs.

Synovial Joints Anatomy

GENERAL FEATURES
  • Freely movable joints characterized by a joint cavity containing synovial fluid and cartilage.
  • Most common joints in the appendicular skeleton, sharing similar anatomical structure.

Focus on Disease: Bursitis

  • Bursa: A small fibrous sac lined with synovial membrane and filled with synovial fluid, found under tendons/ligaments.
  • Bursitis: Inflammation of a bursa, often from overuse or injury, typically affecting the elbow or knee.

Types of Synovial Joints

Uniaxial Joints
  • Hinge joints: e.g. Elbow; allow movement along 1 axis.
  • Pivot joints: e.g. Atlanto-axial joint; cylindrical structure rotates in a ring of bone or ligament.
Biaxial Joints
  • Condyloid joints: e.g. Wrist; allow movement in 2 planes.
  • Saddle joints: e.g. First carpometacarpal joint; similar movements to condyloid joints, but distinctive in structure.
Multiaxial Joints
  • Ball-and-Socket joints: e.g. Shoulder; allow movement in 3 planes.
  • Gliding joints: e.g. Sternocostal; allow slight movements in all directions without identifiable axes of rotation.

Selected Articulations

The Temporomandibular Joint (TMJ)
  • Articulation between the mandibular condyle and the temporal bone; classified as both hinge and gliding joint, allowing motion forward and side-to-side.
Intervertebral Joints
  • Connect vertebral bodies through symphyses, with articular facets via gliding joints; slight movements permitted.
Movement in Vertebral Column
  • Strong ligaments prevent excess motion; the sum of movements includes flexion/extension, lateral flexion, circumduction, and rotation.
Atypical Intervertebral Joints (C1 and C2)
  • C1 (atlas) supports the skull; C2 (axis) contains the dens allowing significant motion due to a double-condyloid structure.
Anatomy of the Shoulder Joint
  • Most freely movable joint; a triaxial ball-and-socket with stabilization from rotator cuff muscles (e.g., supraspinatus, infraspinatus, teres minor, subscapularis).
Anatomy of the Elbow Joint
  • Comprised of:
    • Humeroulnar joint: Hinge joint allowing flexion and extension.
    • Humeroradial joint: Connects capitulum of humerus with the radius.
    • Proximal radioulnar joint: Pivot joint facilitating pronation/supination.
Anatomy of the Knee Joint
  • Largest joint in the body, classified as a modified hinge with limited stability from soft tissue structures including menisci and ligaments.
Focus on Disease: ACL Tears
  • Sprain or tear of the anterior cruciate ligament, commonly caused by trauma or sudden joint movements, treated often with surgical reconstruction.

Clinical Considerations

Temporomandibular Disorder (TMJ Syndrome)
  • Characterized by pain in the temporomandibular joint, caused by misalignment or arthritis; treatments include pain relievers and physical therapy.
Post-CVA Shoulder Subluxation
  • Resulting from loss of motor tone, leading to partial shoulder dislocation; treatment includes supportive positioning.
Developmental Dysplasia of the Hip
  • Subluxation or dislocation of an infant's hip treated by positioning harness or surgery.
Osteoarthritis
  • Chronic degenerative joint disease, causing pain and stiffness, managed with medications for symptom relief and improving joint mobility.
Rheumatoid Arthritis
  • Autoimmune joint disease characterized by swelling and stiffness; treatment includes medications and exercise.
Gout
  • Condition resulting from urate crystal deposition, causing severe pain; treatment focuses on medication for uric acid management.
Nursemaid’s Elbow
  • Separation of the humeroradial joint in children caused by improper pulling; treated by joint reduction.
Lyme Disease
  • Caused by tick-borne bacteria affecting multiple body systems, with musculoskeletal implications; treated with antibiotics.