Joints: Classification, Structure, and Movements (Chapter 9 Study Notes)

Joints and Their Classification

Overview of Joint Classification

Joints, also known as articulations, are points where two bones meet. Their classification is based on the manner in which adjacent bones are bound to each other and the degree of movement permitted.

• Joint Name: Typically derived from the bones involved (e.g., atlanto-occipital joint, glenohumeral joint).

• Classification: Joints are classified by the type of tissue binding the bones and their mobility.

• Four Major Categories:

  • Bony joints (Synostosis)

  • Fibrous joints (Synarthrosis)

  • Cartilaginous joints (Amphiarthrosis)

  • Synovial joints (Diarthrosis)

Bony Joints (Synostosis)

Definition and Examples

Bony joints, or synostoses, are immovable joints formed when the gap between two bones ossifies, resulting in a single bone.

• Examples:

  • Frontal and mandibular bones in infants

  • Cranial sutures in elderly

  • Attachment of first rib and sternum with age

• Can result from ossification of either fibrous or cartilaginous joints.

Fibrous Joints (Synarthrosis)

Types and Structure

Fibrous joints are points where adjacent bones are bound by collagen fibers. They are generally immovable or only slightly movable.

• Three Types:

  • Sutures: Bind skull bones; classified as serrate (interlocking), lap (overlapping), or plane (straight edges).

  • Gomphoses: (Not detailed in slides, but refers to tooth sockets.)

  • Syndesmoses: Bones bound by longer collagenous fibers, allowing more mobility (e.g., interosseous membrane between radius and ulna).

Types of Sutures

Type	Structure	Example
Serrate	Interlocking wavy lines	Coronal, sagittal, lambdoid sutures
Lap (Squamous)	Overlapping beveled edges	Temporal and parietal bones
Plane (Butt)	Straight, nonoverlapping edges	Palatine processes of maxillae

Syndesmosis

• Most movable: Interosseous membrane between radius and ulna (allows supination/pronation).

• Less movable: Tibia to fibula.

Cartilaginous Joints (Amphiarthrosis)

Types and Examples

Cartilaginous joints are where two bones are linked by cartilage, allowing limited movement.

• Two Types:

  • Synchondroses: Bones bound by hyaline cartilage (e.g., epiphyseal plate in children, first rib to sternum).

  • Symphyses: Bones joined by fibrocartilage (e.g., pubic symphysis, intervertebral discs).

Table: Cartilaginous Joint Types

Type	Binding Tissue	Example
Synchondrosis	Hyaline cartilage	Epiphyseal plate, first rib-sternum
Symphysis	Fibrocartilage	Pubic symphysis, intervertebral discs

Synovial Joints (Diarthrosis)

General Anatomy

Synovial joints are the most familiar and freely movable type of joint, characterized by a joint cavity filled with synovial fluid.

• Articular cartilage: Hyaline cartilage covering facing surfaces of bones (2-3 mm thick).

• Joint (articular) cavity: Separates articular surfaces.

• Synovial fluid: Slippery lubricant, rich in albumin and hyaluronic acid; nourishes cartilage and removes waste.

• Joint capsule: Connective tissue enclosing the cavity; consists of an outer fibrous capsule and an inner synovial membrane (fibroblast-like cells and macrophages).

Axes of Rotation

Degrees of Freedom

The axis of rotation is a stationary line about which a bone moves. Joints are classified by the number of axes:

• Multiaxial: Shoulder joint (three degrees of freedom).

• Biaxial: Movement in two planes.

• Monoaxial: Movement in one plane.

Classes of Synovial Joints

Types and Examples

Type	Structure	Example	Axes
Ball-and-Socket	Hemisphere head in cup socket	Shoulder, hip	Multiaxial
Condyloid (Ellipsoid)	Oval convex fits depression	Radiocarpal, metacarpophalangeal	Biaxial
Saddle	Both surfaces saddle-shaped	Thumb (trapeziometacarpal), sternoclavicular	Biaxial
Plane (Gliding)	Flat surfaces slide	Carpal, tarsal, vertebral processes	Biaxial
Hinge	Convex fits concave	Elbow, knee, fingers, toes	Monoaxial
Pivot	Projection held by ring ligament	Atlantoaxial, proximal radioulnar	Monoaxial

Movements of Synovial Joints

Vocabulary and Zero Position

Movements are described relative to the anatomical position (zero position). Understanding anatomical planes and directional terms is essential.

• Flexion: Decreases joint angle (common in hinge joints).

• Extension: Straightens joint, returns to zero position.

• Hyperextension: Extension beyond zero position.

• Abduction: Moves body part away from midline in frontal plane.

• Adduction: Moves body part toward midline.

• Elevation: Raises body part vertically.

• Depression: Lowers body part vertically.

• Protraction: Anterior movement in transverse plane.

• Retraction: Posterior movement.

• Circumduction: Circular motion with stationary end.

• Rotation: Bone spins on longitudinal axis (medial/lateral).

• Supination: Forearm turns palm anterior/upward.

• Pronation: Forearm turns palm posterior/downward.

Special Movements

Head, Trunk, Mandible, and Foot

• Head and Trunk: Flexion, hyperextension, lateral flexion, right/left rotation.

• Mandible: Lateral/medial excursion, protraction, retraction, elevation, depression.

• Foot: Dorsiflexion, plantar flexion, inversion, eversion.

Arthritis and Joint Disorders

Types and Treatments

• Arthritis: Pain and inflammation of a joint; most common crippling disease in the U.S.

• Osteoarthritis (OA): 'Wear-and-tear' arthritis; degeneration of articular cartilage, bone spurs, crepitus.

• Rheumatoid Arthritis (RA): Autoimmune attack on joint tissues; synovial membrane degradation, ankylosis (fusion).

• Arthroplasty: Replacement of diseased joint with artificial prosthesis.

Table: Arthritis Types

Type	Cause	Features
Osteoarthritis	Wear and tear	Cartilage degeneration, bone spurs
Rheumatoid Arthritis	Autoimmune	Synovial membrane attack, ankylosis

Summary Table: Joint Types and Examples

Joint Type	Binding Tissue	Mobility	Example
Bony (Synostosis)	Bone	Immovable	Frontal bone, cranial sutures (elderly)
Fibrous (Synarthrosis)	Collagen fibers	Immovable/slightly movable	Sutures, syndesmoses
Cartilaginous (Amphiarthrosis)	Cartilage	Slightly movable	Epiphyseal plate, pubic symphysis
Synovial (Diarthrosis)	Synovial cavity	Freely movable	Shoulder, knee, hip

Additional info: The notes have been expanded with definitions, examples, and tables for clarity and completeness, suitable for college-level Anatomy & Physiology study.