Study Notes on Types of Joints and Their Functions
Types of Joints
Definition of Joints (Articulations)
Functional connections between bones: Joints act as pivot points for movement between skeletal bones.
Bind parts of skeletal system together: They provide structural integrity to the skeleton.
Enable bone growth: Joints allow for the growth of bones during development.
Permit shape change during childbirth: Joints adapt to accommodate the delivery process.
Facilitate movement: They allow the body to move in response to skeletal muscle contractions.
Structural Classification of Joints
Types of Structural Classification
Fibrous Joints:
Held together by dense connective tissue.
Cartilaginous Joints:
Held together by cartilage.
Synovial Joints:
Have a complex structure involving a joint cavity.
Types of Functional Classification
Synarthrotic:
Immovable joints.
Amphiarthrotic:
Slightly movable joints.
Diarthrotic:
Freely movable joints.
Fibrous Joints
Definition
Fibrous joints are held together with dense connective tissue that contains a high concentration of collagen fibers.
Commonly found in bones that are in close contact.
Types of Fibrous Joints
Syndesmosis:
Description: Bones are bound by a sheet of dense connective tissue (interosseous membrane) or a bundle of dense connective tissue (interosseous ligament).
Movement: Amphiarthrotic (flexible, may twist).
Example: Joint between the tibia and fibula.
Suture:
Description: A thin layer of connective tissue (sutural ligament) connects the bones.
Movement: Synarthrotic (immovable).
Example: Joints between the flat bones of the skull.
Gomphosis:
Description: A cone-shaped bony process that fits into a socket.
Movement: Synarthrotic (immovable).
Example: Root of a tooth in the maxilla or mandible, held in place by the periodontal ligament.
Cartilaginous Joints
Definition
Cartilaginous joints are connected by either hyaline cartilage or fibrocartilage.
Types of Cartilaginous Joints
Synchondrosis:
Description: Bands of hyaline cartilage unite the bones.
Movement: Synarthrotic.
Notes: Some synchondroses (e.g., epiphyseal plate) are temporary and become a synostosis through ossification, while others are permanent (e.g., between the manubrium and the first rib).
Symphysis:
Description: A pad of fibrocartilage lies between the bone surfaces, with articular surfaces covered by hyaline cartilage.
Movement: Amphiarthrotic (limited movement).
Examples: Pubic symphysis and intervertebral discs (joint between bodies of adjacent vertebrae).
Synovial Joints
Definition
Synovial joints are the most common type of joint and all are classified as diarthrotic.
They have a complex structure with several distinct components.
Structure of a Synovial Joint
Articular Cartilage: Covers the articular ends of bones to reduce friction.
Joint Capsule: Comprises two layers:
Outer Fibrous Layer: Composed of ligaments that provide stability.
Inner Synovial Membrane: Secretes synovial fluid for lubrication.
Components of a Synovial Joint
Articular cartilage
Joint capsule
Ligaments
Synovial membrane
Synovial cavity
Synovial fluid
Meniscus (-i) in some joints
Bursa (-ae) in some joints
Types of Synovial Joints
Overview
Six types classified by shape and allowed movements:
Ball-and-Socket Joint:
Also known as spheroidal joint, characterized by a round head fitting into a cup-shaped cavity.
Movement: Multiaxial with rotation (widest range of motion).
Examples: Hip, shoulder.
Condylar Joint:
Also known as ellipsoidal joint, where an oval condyle fits into an elliptical cavity.
Movement: Biaxial (back-and-forth, side-to-side) with no rotation.
Example: Joints between metacarpals and phalanges.
Plane Joint:
Also known as gliding joint, featuring nearly flat surfaces.
Movement: Nonaxial (back-and-forth and twisting).
Examples: Wrist and ankle joints.
Hinge Joint:
Features a convex surface fitting into a concave surface of another bone.
Movement: Uniaxial (in one plane).
Examples: Elbow and joints between phalanges.
Pivot Joint:
Also called trochoid joint, with a cylindrical surface rotating within a ring of another bone.
Movement: Uniaxial (rotation only).
Example: Joint between atlas (C1) and dens of axis (C2).
Saddle Joint:
Also known as sellar joint, where both bones have concave and convex surfaces.
Movement: Biaxial (in two planes).
Example: Joint between carpal and metacarpal of the thumb.
Types of Joint Movements
Description of Movements
Action of Skeletal Muscle: Movement occurs at synovial joints when a muscle contracts, pulling the insertion toward the origin.
Definitions of Movements:
Flexion: Bending at a joint.
Extension: Straightening at a joint.
Hyperextension: Extension beyond the normal anatomical position.
Lateral Flexion: Bending of the torso to the side.
Abduction: Movement away from the midline of the body.
Adduction: Movement toward the midline of the body.
Dorsiflexion: Ankle movement that points the toes upward.
Plantar Flexion: Ankle movement that points the toes downward.
Circumduction: Circular movement of a body part.
Rotation: Movement around an axis.
Medial Rotation: Rotation of a limb so that the anterior surface moves toward the midline.
Lateral Rotation: Rotation of a limb so that the anterior surface moves away from the midline.
Supination: Forearm rotation that turns the palm upward or forward; lying face up (supine).
Pronation: Forearm rotation that turns the palm downward or backward; lying face down (prone).
Inversion: Turning the foot so that the plantar surface faces the midline.
Eversion: Turning the foot so that the plantar surface faces away from the midline.
Protraction: Movement of a body part forward.
Retraction: Movement of a body part backward.
Elevation: Raising a body part.
Depression: Lowering a body part.
Examples of Synovial Joints
Common examples of large, complex synovial joints include:
Shoulder
Elbow
Hip
Knee
Specific Joint Examples
Shoulder Joint
Type: Ball-and-socket joint.
Components: Head of humerus and glenoid cavity of scapula.
Features: Loose joint capsule, ligaments to prevent displacement, glenoid labrum, several bursae.
Movement: Wide range, including rotation and circumduction.
Major Ligaments:
Coracohumeral ligament
Glenohumeral ligaments
Transverse humeral ligament
Elbow Joint
Articulations: Contains two articulations:
Hinge Joint: Between trochlea of humerus and trochlear notch of ulna (flexion/extension only).
Plane Joint: Between capitulum of humerus and fovea on head of radius (pronation/supination).
Reinforcing Ligaments:
Radial collateral ligament
Ulnar collateral ligament
Anular ligament
Hip Joint
Type: Ball-and-socket joint.
Components: Head of femur and acetabulum of hip bone.
Features: Acetabular labrum, heavy joint capsule, numerous reinforcing ligaments.
Major Ligaments:
Iliofemoral ligament (strongest in the body)
Pubofemoral ligament
Ischiofemoral ligament
Knee Joint
Description: Largest and most complex synovial joint, consisting of three bones: femur (medial and lateral condyles), tibia (medial and lateral condyles), and patella (articulating with femur).
Features: Strengthened by many ligaments, cushioned by bursae and fat pads, with menisci separating femur and tibia.
Type: Modified hinge joint and planar joint between femur and patella.
Movements: Flexion/extension and some rotation when knee is flexed.
Ligaments of the Knee Joint
Major Ligaments:
Patellar ligament
Oblique popliteal ligament
Arcuate popliteal ligament
Tibial (medial) collateral ligament
Fibular (lateral) collateral ligament
Anterior cruciate ligament
Posterior cruciate ligament
Joint Disorders
Causes of Joint Injuries: Trauma, overuse, infection, inappropriate immune response, degeneration.
Diagnosis and Treatment: Arthroscopy is utilized for treatment of injuries to the shoulder, elbow, and knee; can also diagnose conditions.
Common Joint Injuries:
Dislocations: Displacement of bone surfaces; frequently occurs in shoulder, knee, fingers, jaw.
Sprain: Tearing of connective tissue in joints without dislocation.
Torn Ligament: Results from twisting, overextension, lifting heavy objects, or falls.
Bursitis: Inflammation of a bursa due to overuse or stress.
Arthritis: Inflammation, swelling, and pain in joints, with subtypes including:
Rheumatoid arthritis (autoimmune disease).
Osteoarthritis (degenerative, common with aging).
Lyme arthritis (caused by Lyme disease from tick bites).
Replacing Joints
Joint Replacement Materials: Synthetic materials used to replace damaged joints due to arthritis or injury; steel and titanium are common for larger joints, while silicone is used for smaller ones. Ceramic materials may also be utilized.
Common Procedures: Hip replacements are the most frequent surgery.
New Technologies: Innovations include materials resembling natural body chemicals (e.g., hydroxyapatite-coated implants) and 3D printing technology for creating custom joint replacements.
Lifespan Changes
Aging Effects on Joints:
Joint stiffness is an early indicator of aging.
Arthritis often develops with age.
Fibrous joints may change first, potentially strengthening over a lifetime.
Cartilage in synchondroses may stiffen.
Ligaments may lose elasticity over time.
Changes in symphysis joints of the vertebral column can reduce flexibility and decrease height due to water loss from intervertebral discs.
Synovial joints may lose function as capillary supply diminishes.
Disuse can speed up stiffness due to nutrient supply hampering.
Regular activity and exercise can help in maintaining joint function longer.