Joint Classification: Fibrous, Cartilaginous, Synovial

Joint Classification

• Joints are classified by structure and function.
• Structural classification is based on the material binding bones together: fibrous, cartilaginous, and synovial.
• Functional classification is based on the amount of movement allowed: synarthrosis (immovable), amphiarthrosis (slightly movable), and diarthrosis (freely movable).

Fibrous Joints

• Bones are connected by dense connective tissue.
• Movement ranges from little to none.
• Sutures are immovable joints found in the skull.
• Syndesmoses are slightly movable, such as the tibia and fibula.
• Gomphoses are peg-in-socket joints, like teeth in the jaw.

Cartilaginous Joints

• Synchondroses use hyaline cartilage and are mostly immovable, like epiphyseal plates.
• Symphyses use fibrocartilage and are slightly movable, such as the pubic symphysis.

Synovial Joints

• These joints have a joint cavity filled with synovial fluid.
• Articular cartilage, a fibrous capsule, and reinforcing ligaments are present.
• Articular cartilage reduces friction.
• Synovial fluid lubricates and nourishes.
• The joint capsule encloses the joint.
• Ligaments stabilize the joint.
• Bursae reduce friction between tissues.

Synovial Joint Types

• Plane (gliding) joints are present in intercarpal joints.
• Hinge joints can be found in the elbow.
• Pivot joints are in the atlantoaxial joint.
• Condylar (ellipsoid) joints are present in the wrist.
• Saddle joints are in the thumb (carpometacarpal joint).
• Ball-and-socket joints are found in the shoulder and hip.
• Uniaxial joints allow movement in one plane (hinge, pivot).
• Biaxial joints permit movement in two planes (condylar, saddle).
• Multiaxial joints allow movement in multiple planes (ball-and-socket).

Joint Movements

• Gliding involves sliding movements, such as in intercarpal joints.
• Angular movements change the angle (flexion, extension).
• Circular movements include rotation and circumduction.
• Special movements are unique, like supination and pronation.
• Flexion is bending; extension is straightening.
• Plantar flexion is pointing the foot; dorsiflexion is raising the foot.
• Abduction moves away from the midline; adduction moves toward the midline.
• Supination turns the palm up; pronation turns the palm down.
• Elevation raises a body part; depression lowers a body part.
• Protraction moves forward; retraction moves backward.
• Opposition touches the thumb to fingers; reposition returns the thumb.
• Inversion turns the foot inward; eversion turns the foot outward.

Rotation, Circumduction, and Excursion

• Rotation turns around a fixed axis, like neck rotation.
• Circumduction combines flexion, extension, abduction, and adduction in a circular motion.
• Excursion is side-to-side movement, such as lateral jaw movement.

Range of Motion

• Active range of motion is movement performed by the individual.
• Passive range of motion is movement performed by an external force.
• Exceeding normal range of motion can cause ligament tears, joint dislocations, and cartilage damage.
• Factors affecting range of motion include joint structure, ligament flexibility, muscle strength and tone, and injury or disease.

Major Joints

• The temporomandibular joint (TMJ) is a modified hinge joint that allows gliding and rotational movements.
• The shoulder is more mobile but less stable than the hip.
• The hip is more stable but less mobile than the shoulder.
• The elbow is a strong hinge joint with limited movement.
• The knee is a complex hinge joint that allows slight rotation.
• The ankle provides hinge motion with slight side movement.
• ACL, PCL, MCL, and LCL ligaments stabilize knee movement.
• Arches of the foot provide support and shock absorption.

Common Joint Disorders

• Arthritis is inflammation of the joint (osteoarthritis, rheumatoid arthritis).
• Bursitis is inflammation of bursae.
• Dislocations occur when bones are forced out of position.