Anatomy & Physiology: Chapter 8 – Joints (Articulations)

Joints (Articulations)

Introduction to Joints

Joints, also known as articulations, are the locations where two or more bones meet. They play a crucial role in providing movement and flexibility to the skeleton, as well as stability and support.

• Range of Motion (ROM): Refers to the degree of movement possible at a joint.

• Function: Joints allow for movement, support, and protection of the body.

• Classification: Joints are classified based on their structure and the amount of movement they permit.

Key Example: The joints of the axial skeleton include sutures of the skull, temporomandibular joint, atlanto-occipital joint, intervertebral joints, and sacrococcygeal joint.

Classification of Joints

Main Types of Joints

Joints are classified into three main categories based on their structure and function:

• Fibrous Joints: Immovable joints (synarthroses)

• Cartilaginous Joints: Slightly movable joints (amphiarthroses)

• Synovial Joints: Freely movable joints (diarthroses)

Additional info: The degree of movement allowed by a joint is directly related to its structural type.

Fibrous Joints

General Features

Fibrous joints are connected by dense fibrous connective tissue and typically permit little or no movement.

• Types of Fibrous Joints:

  • Sutures

  • Gomphoses

  • Syndesmoses

Sutures

Definition: Sutures are joints united by a thin layer of fibrous tissue, found only between the flat bones of the skull.

• Movement: Allow a small amount of movement early in life; become immovable later in life as the bones fuse.

• Example: The coronal suture between the frontal and parietal bones.

Gomphoses

Definition: Gomphoses are joints where a peg-in-hole shaped bone is united by fibrous material, such as the attachment of teeth to their sockets.

• Movement: Slight movement of teeth to mandible or maxilla early in life; become immovable later in life.

• Example: The joint between a tooth and the alveolar socket of the mandible or maxilla.

Syndesmoses

Definition: Syndesmoses are joints united by a fibrous ligament or interosseous membrane.

• Movement: Slightly movable.

• Examples:

  • Interosseous membrane between the radius and ulna in the forearm

  • Interosseous membrane between the tibia and fibula in the leg

Cartilaginous Joints

General Features

Cartilaginous joints are connected by cartilage and allow for limited movement. They are classified as amphiarthroses.

• Types:

  • Symphyses

  • Synchondroses

Additional info: These joints are important for shock absorption and flexibility in the axial skeleton.

Synovial Joints

General Features

Synovial joints are the most movable type of joint in the body. They are characterized by a synovial cavity filled with synovial fluid, which reduces friction and allows for a wide range of movements.

• Types:

  • Hinge

  • Pivot

  • Condyloid (Ellipsoid)

  • Saddle

  • Ball and Socket

  • Gliding (Plane)

Additional info: Synovial joints are found in the limbs and are essential for locomotion and manipulation.

Summary Table: Joint Classification

Joint Type	Structural Feature	Movement	Example
Fibrous	Dense fibrous connective tissue	Immovable or slightly movable	Sutures of the skull, gomphoses (teeth), syndesmoses (radius/ulna)
Cartilaginous	Cartilage (hyaline or fibrocartilage)	Slightly movable	Intervertebral discs, pubic symphysis
Synovial	Synovial cavity, articular cartilage	Freely movable	Shoulder, hip, knee, elbow

Key Terms and Definitions

• Articulation: The site where two or more bones meet.

• Synarthrosis: An immovable joint.

• Amphiarthrosis: A slightly movable joint.

• Diarthrosis: A freely movable joint.

• Synovial Fluid: Lubricating fluid found within synovial joints.

Clinical Relevance

• Osteoarthritis (OA): Degeneration of joint cartilage and underlying bone, often due to wear and tear or injury.

• Rheumatoid Arthritis (RA): An autoimmune disorder causing inflammation and destruction of joint tissues.

• Joint Replacement: Surgical procedures such as total shoulder, hip, knee, or ankle arthroplasty are performed to restore function in severely damaged joints.