Chapter 9: Joints – Structure, Classification, and Movement

Joints and Movement

Definition of a Joint

A joint (also called an articulation) is the place where adjacent bones or bone and cartilage come together to form a connection. Joints are essential for movement and stability in the skeletal system.

• Articulation: The point of contact between bones, or between bone and cartilage.

Factors Affecting Joints

Determinants of Joint Type and Movement

The type of joint and the range of movement it allows are determined by:

• Structure of the joint: The physical composition and arrangement of the joint.

• Function of the joint: The degree and type of movement permitted.

Structural Classification of Joints

Overview of Structural Classification

Structural classification of joints is based on how the bones are connected and whether a joint cavity is present. The three main types are:

• Fibrous joint

• Cartilaginous joint

• Synovial joint

Fibrous Joints

In fibrous joints, adjacent bones are directly connected by fibrous connective tissue. These joints do not have a joint cavity and allow little to no movement.

• Suture: Found between skull bones; immobile.

• Gomphosis: The joint of a tooth within its socket in the maxilla or mandible.

Cartilaginous Joints

Cartilaginous joints are where bones are joined by cartilage (either hyaline or fibrocartilage). These joints allow more movement than fibrous joints but less than synovial joints.

• Synchondrosis: Bones are joined by hyaline cartilage. Examples include:

  • Temporary: Epiphyseal plate (growth plate), sacral bone, coxal bone.

  • Permanent: Ribs at the costochondral margins (costal cartilage).

• Symphysis: Bones are joined by fibrocartilage (which is tougher than hyaline cartilage). Examples include:

  • Pubic symphysis

  • Intervertebral symphysis (between vertebral bodies)

Synovial Joints

Synovial joints are characterized by the presence of a fluid-filled joint cavity that allows for free movement between the bones. These are the most common and most movable type of joint in the body.

• Articulating surfaces are not directly connected but come into contact within a synovial cavity.

• Examples: Shoulder, knee, elbow, hip joints.

Functional Classification of Joints

Overview of Functional Classification

Joints can also be classified by the amount of movement they allow:

• Synarthrosis: Immobile joint (e.g., sutures of the skull).

• Amphiarthrosis: Slightly mobile joint (e.g., pubic symphysis, intervertebral discs).

• Diarthrosis: Freely movable joint (all synovial joints).

Summary Table: Structural and Functional Classification of Joints

Structural Type	Examples	Functional Type	Mobility
Fibrous (Suture, Gomphosis)	Skull sutures, tooth in socket	Synarthrosis	Immobile
Cartilaginous (Synchondrosis, Symphysis)	Epiphyseal plate, pubic symphysis, intervertebral discs	Amphiarthrosis	Slightly mobile
Synovial	Shoulder, knee, hip, elbow	Diarthrosis	Freely movable

Key Terms and Concepts

• Articulation: The point where two bones meet.

• Synarthrosis: Immovable joint.

• Amphiarthrosis: Slightly movable joint.

• Diarthrosis: Freely movable joint.

• Hyaline cartilage: Smooth cartilage that covers the ends of bones in synovial joints and forms synchondroses.

• Fibrocartilage: Tough cartilage found in symphyses.

Examples and Applications

• Sutures: Immobile joints in the skull that protect the brain.

• Gomphosis: The joint that anchors teeth in their sockets.

• Synchondrosis: The epiphyseal plate in growing children, which allows for bone growth.

• Symphysis: The pubic symphysis, which allows for slight movement during childbirth.

• Synovial joints: The knee and shoulder, which allow for a wide range of motion necessary for daily activities.

Additional info: Later sections of the chapter would likely cover the detailed anatomy of synovial joints, types of synovial joints, and specific joint movements.