Anatomy & Physiology Study Notes: Introduction to Joints

Introduction to Joints

The human skeleton contains over 200 bones, and nearly all of them connect to other skeletal elements at joints. Joints, also known as articulations or arthroses, are contact points between two or more bones, or between a bone and a tooth. Joints may also include cartilage, ligaments, tendons, and muscles.

• Key Functions of Joints:

  • Facilitate skeletal movement

  • Provide stability to the skeleton

• The greater the range of motion, the less stable the joint is.

Examples of Joints:

• Finger joints

• Shoulder joint

• Bone-to-tooth joint

Application: Dislocation of the shoulder joint is a common injury because most sports put a lot of stress on the shoulder joint, and people often try to lift things that are too heavy.

Classification of Joints

Functional Classes of Joints

Joints are classified by the amount of movement they allow:

• Synarthrosis (S): Stationary joint with basically no movement (immovable joint). Often found in the axial skeleton.

• Amphiarthrosis (A): Slightly moveable joint with little or "average" movement.

• Diarthrosis (D): Dynamic and freely moveable joint (predominant in the appendicular skeleton).

Example: Rheumatoid arthritis causes pain when joints move. Diarthroses are most likely affected because they allow the greatest range of motion.

Structural Classes of Joints

Structural classification is based on the binding material used between skeletal elements:

• Fibrous Joints: Bones bound by collagen fibers of dense connective tissue. Always synarthrosis or amphiarthrosis.

• Cartilaginous Joints: Bones bound by cartilage. Always synarthrosis or amphiarthrosis.

• Synovial Joints: Bones have a synovial cavity and are bound by ligaments within an articular capsule. Always diarthrosis.

Table: Joint Classification Overview

Functional Class	Structural Class	Movement Allowed	Example
Synarthrosis	Fibrous, Cartilaginous	None	Sutures of skull
Amphiarthrosis	Fibrous, Cartilaginous	Slight	Intervertebral joints
Diarthrosis	Synovial	Free movement	Knee joint

Fibrous Joints

Fibrous joints are skeletal elements bound by dense irregular connective tissue. They allow little or no movement and are classified as synarthroses or amphiarthroses.

• Sutures: Only join bones of the skull. Provide structural support but allow little movement. As the brain grows, sutures ossify to form a synostosis (bony joint) in adults.

• Gomphoses: Joints between teeth and their sockets.

• Syndesmoses: Joints where bones are connected by a ligament or interosseous membrane, allowing slight movement.

Example: In a baby, the bones of the skull are joined by fibrous connective tissue. Over time, these bones fuse together to form ossified immovable joints (synostoses).

Practice Questions & Applications

• Which of the following is a correct description of syndesmoses?

  • Fibrous amphiarthrosis

• Which joint classification is not based on the joint's range of motion?

  • Synovial

• Which scenario is most concerning for a pediatric patient?

  • The epiphyseal plate in their femur is not fully ossified.

Additional Info

• Ossification: The process by which bone tissue forms, leading to the fusion of bones at joints such as sutures in the skull.

• Synostosis: A type of joint where two bones have fused together, eliminating the joint space.

• Arthritis: A common disease associated with joints, often affecting those that allow movement (diarthroses).