Anatomy of Joint Types and Functions

Chapter 9: Articulations

• Articulations are where bones meet, allowing various types and ranges of movement.
• Bones are rigid; articulations enable flexibility through their structure and supporting tissues.
• Arthrology is the scientific study of joints.

Classification of Joints

• Joints (articulations) are classified by structural characteristics and the type of movement they allow.

• Fibrous joints have no joint cavity and are held together by dense connective tissue. Examples include sutures (e.g., in the skull), gomphoses (e.g., teeth in sockets), and syndesmoses (e.g., between radius and ulna).

• Cartilaginous joints also lack a joint cavity and join bones via cartilage. Examples include synchondroses (e.g., epiphyseal plates, first rib to sternum) and symphyses (e.g., pubic symphysis, intervertebral discs).

• Synovial joints have a fluid-filled joint cavity separating articulating bone surfaces. The surfaces are enclosed within connective tissue, and bones are attached by ligaments. Examples are elbow, knee, and shoulder joints.

• Each joint type has a specific range of motion, from immobile (synarthroses) to freely mobile (diarthroses).

Functional Classification of Joints

• Synarthroses are immobile joints - fibrous or cartilaginous joints.

• Amphiarthroses are slightly mobile - fibrous or cartilaginous joints.

• Diarthroses are freely mobile joints - all synovial joints.

Range of Motion at Joints

• The structure of each joint dictates its stability and mobility.
• There's a tradeoff between mobility and stability; high mobility often comes with lower stability, and vice versa.

Fibrous Joints

• Characterized by dense regular connecting tissue.
• No joint cavity.
• Can be immovable or slightly mobile.
• Three common types: gomphoses, sutures, and syndesmoses.

Fibrous Joints: Gomphoses

• "Peg-in-socket" articulation.
• Only found in teeth within their sockets of the mandible and maxilla.

Fibrous Joints: Sutures

• Immovable fibrous joints only between certain skull bones.
• Interlocking edges increase skull strength and reduce fractures during childhood growth.
• Eventually fuse to become synostoses (completely fused).

Fibrous Joints: Syndesmoses

• Joined by long strands of connective tissue.
• Allow for slight mobility (amphiarthroses).
• Examples include the interosseous membrane between the radius and ulna.

Cartilaginous Joints

• Have cartilage connecting articulating bones (hyaline or fibrocartilage).
• Lack a joint cavity.
• Can be immovable or slightly mobile.
• Two main types: synchondroses and symphyses.

Cartilaginous Joints: Synchondroses

• Joined by hyaline cartilage.
• Immobile (synarthroses).
• Examples include epiphyseal plates and the first rib to sternum.

Cartilaginous Joints: Symphyses

• Joined by fibrocartilage.
• Slightly mobile (amphiarthroses).
• Example includes intervertebral discs and pubic symphysis.
• Acts as shock absorber.

Clinical View: Costochondritis

• Inflammation of the costochondral joints, causing localized chest pain.
• Usually unknown cause.

Synovial Joints: Distinguishing Features and Anatomy

• Synovial joints are freely moveable.
• Bones are separated by a joint cavity. They are lined by a synovial membrane.
• The joint cavity contains synovial fluid that lubricates, nourishes, and acts as a shock absorber.
• Synovial joints have an articular capsule (fibrous layer and synovial membrane).
• The articular capsule contains ligaments, sensory nerves, and blood vessels.

Synovial Joints: Articular Cartilage

• Hyaline cartilage covers articulating surfaces.
• Reduces friction.
• Absorbs shock.
• Prevents damage.
• Lacks perichondrium.

Synovial Joints: Joint Cavity

• Separates articulating bone surfaces.
• Lined with synovial membrane that secretes synovial fluid.
• Synovial fluid is a viscous, oily substance lubricating articulating cartilage; nutrient transport.

Synovial Joints: Ligaments

• Dense regular connective tissue connecting bones.
• Stabilize and strengthen synovial joints.
• Some ligaments are extrinsic (physically separate from the capsule); others are intrinsic (thickening of the capsule itself).

Synovial Joints: Other Accessory Structures

• Tendons: Dense regular connective tissue attaching muscles to bones; often help stabilize or limit movement at the joint.
• Bursae: Fibrous sacs containing synovial fluid, reducing friction between bones, tendons, or muscles.
• Tendon sheaths: Elongated bursae wrapped around tendons—especially common in areas of high friction like wrists and ankles.
• Fat pads: Act as packing material; cushion joints.

Synovial Joints: Classification

• Classified by shape of articulating surfaces and type of movement allowed (uniaxial, biaxial, multiaxial).

• Types of Synovial Joints: Plane, Hinge, Pivot, Condylar, Saddle, Ball-and-Socket

Movements of Synovial Joints

• Gliding: Side-to-side or back-and-forth movement of bones.
• Angular: Increases or decreases the angle between bones.
• Flexion: Decreasing angle
• Extension: Increasing angle
• Hyperextension: Extending beyond the normal range
• Lateral flexion: Bends the vertebral column laterally
• Abduction: Moving a structure away from the midline
• Adduction: Moving a structure toward the midline
• Circumduction: Moving a distal part of the body in a circle.
• Rotation: Pivoting around a longitudinal axis.
• Lateral rotation: Turns front of a structure away from the midline
• Medial rotation: Turns front of a structure toward the midline
• Pronation: Medial rotation of forearm so palm faces posteriorly
• Supination: Lateral rotation of forearm so palm faces anteriorly.

Knee Joint

• Largest and most complex diarthrosis in the body.
• Primarily a hinge joint.
• Composed of tibiofemoral and patellofemoral articulations.
• Contains cruciate ligaments (ACL and PCL), collateral ligaments (medial and lateral), and menisci (medial and lateral). The articular capsule encloses regions of medial, lateral, and posterior aspects of the knee.

Knee Injuries

• Common injuries involve collateral, cruciate ligaments, and the menisci.

Notes on the images

• Images showcase anatomical structures, and X-ray or MRI modalities.
• Many images illustrate examples of the various joint types.

Test your knowledge on the various types of joints in the human body, specifically focusing on fibrous and cartilaginous joints. This quiz covers their functions, characteristics, and structural differences. Understand the relationship between mobility and stability as it pertains to joint anatomy.