Joints

Importance of Joints
- In Australia, approximately 1.7 million doctor-patient interactions are related to sprains or strains.
- Common causes of joint issues include acute traumas like sprains from falls or slips.
- Example: Terrible triad - ACL (anterior cruciate ligament), MCL (medial collateral ligament), and medial meniscus injuries occurring simultaneously in knees.
- Chronic issues include inflammatory or degenerative conditions (e.g., arthritis), sometimes leading to joint replacements.
Learning Objectives
- Understand the structure of joints and their function
- Classify joints by both structure and function.
- Define possible movements at different types of joints.
Functions of Joints
- Joints provide mobility to the skeleton while maintaining structural integrity to avoid dislocation.
- Varied types of joints present different degrees of movement, depending on structure.

Classification of Joints
- Joints classified by structure (material binding bones and joint cavity) and function (degree of movement).
- Names of Structural Classifications
  - Fibrous joints: No movement; bones connected by fibrous tissue.
    - Examples: Syndesmosis (joined by ligament), Sutures (interlocking short joints in skull).
  - Cartilaginous joints: Slight movement; connected by cartilage.
    - Synchondrosis (hyaline cartilage plates) and Symphysis (fibrocartilage).
  - Synovial joints: Most common, feature a fluid-filled cavity, high mobility.
Functional Classifications
- Synarthroses: No movement.
- Amphiarthroses: Slight movement.
- Diarthroses: Freely movable; all synovial joints fall into this category.

Distinguishing Features of Synovial Joints
- Articular Cartilage: Covers bone ends to prevent damage.
- Joint Cavity: Contains synovial fluid for lubrication.
- Articular Capsule: Holds the joint together, enclosing synovial fluid.
- Associated Structures:
  - Menisci: Fibrocartilaginous discs improving bone fit.
  - Fat Pads: Provide cushioning during high impact activities.
  - Tendons and Ligaments: Tendons connect muscles to bones; ligaments connect bones to bones.
  - Bursa: Fluid-filled sacs that cushion joints; can become inflamed (bursitis).
Movement Constraints
- Movement is limited by the shape of articulating surfaces, ligaments, and muscle tension.

Classification of Movements
- Non-axial: Slipping movements (e.g., carpal bones).
- Uniaxial: Movement in one plane (e.g., elbow).
- Biaxial: Movement in two planes (e.g., wrist).
- Multiaxial: Movement in multiple planes (e.g., shoulder joint).
- Types of Movement
  - Gliding: Flat bones glide past each other.
  - Flexion and Extension: Decrease or increase the angle between bones.
  - Abduction and Adduction: Movement away from and towards the midline.
  - Circumduction: Circular movement of a limb.

Ankle Joint Structure
- Comprised of the tibia, fibula, and talus; classified as a uniaxial hinge joint but allows for inversion/eversion at subtalar joint.
Types of Synovial Joints
- Gliding Joints: Allow slight movement.
- Hinge Joints: Allow flexion/extension (e.g., elbow, knee).
- Pivot Joints: Permit rotation along a long axis (e.g., proximal radioulnar joint).
- Condyloid and Saddle Joints: Allow for biaxial movements, flexion, extension, abduction, and adduction.
- Ball and Socket Joints: Multi-axial movements (e.g., shoulder and hip joints).

Common Joint Injuries
- Sprains: Ligament injuries, often require long recovery due to poor blood supply.
- Dislocations: Ligaments forced out of place; partial dislocations termed subluxations.
- Cartilage Tears: Particularly found in the meniscus; often require surgical intervention.
- Arthritis: Common degenerative disease of the joints; includes osteoarthritis (wear and tear) and rheumatoid arthritis (autoimmune).
- Joint Replacements: Severe cases necessitate surgical replacement of damaged joints.