Anatomy & Physiology: The Skeletal System – Joints

Unit 3: Skeletal System

Lesson 4: Joints

This lesson explores the anatomy and physiology of joints, focusing on their classification, structure, function, and clinical significance within the skeletal system.

Learning Outcomes

• Define terminology pertinent to the anatomy and physiology of joints.

• Identify and describe the structural (anatomic) components of joints and their significance.

• Explain the function (physiology) of joint components.

• List and describe the steps in significant processes involving joints and explain their importance to the body.

• Apply anatomical and physiological knowledge of joints to clinical examples.

Joints: Introduction

Joints (also called articulations) are the locations where two or more bones meet. They are essential for movement and stability in the skeletal system.

• Hold bones together and allow for movement.

• May involve direct bone-to-bone contact, cartilage, or fibrous tissue.

• Some joints connect bone to cartilage or teeth to bone (e.g., gomphosis).

Classification of Joints

By Structure

Structural classification is based on the anatomical components that connect the bones:

• Fibrous joints: Bones joined by dense connective tissue; no joint cavity.

• Cartilaginous joints: Bones joined by cartilage; no joint cavity.

• Synovial joints: Bones separated by a fluid-filled joint cavity.

By Function

Functional classification is based on the degree of movement permitted:

• Synarthrosis: Immovable joint (e.g., suture in the skull, gomphosis between teeth and jaw).

• Amphiarthrosis: Slightly movable joint (e.g., symphysis pubis, intervertebral discs).

• Diarthrosis: Freely movable joint (synovial joints), further subdivided by their plane of movement.

Structural Classifications

Fibrous Joints

• Bones are closely joined by dense connective tissue.

• Allow little or no movement.

• Examples: Sutures in the skull, syndesmoses, gomphoses.

Cartilaginous Joints

• Allow little or no movement.

• Bones are tightly connected by fibrocartilage or hyaline cartilage.

• Examples: Symphysis pubis, sternal angle.

Synovial Joints

• Most common and movable type of joint in the body.

• Characterized by a synovial cavity filled with synovial fluid.

• Articulating bone surfaces are covered with articular cartilage.

Components of Synovial Joints

• Articular cartilage: Covers bone surfaces, reduces friction.

• Joint (articular) capsule: Encloses the joint cavity; composed of fibrous tissue.

• Synovial membrane: Lines the inner surface of the capsule; produces synovial fluid.

• Synovial fluid: Lubricates the joint, nourishes articular cartilage, absorbs shock.

• Ligaments: Strengthen and stabilize the joint.

• Accessory structures: Include cartilage and fat pads, tendons, and bursae.

Accessory Structures

• Cartilage and fat pads: Provide cushioning and support.

• Ligaments: Connect bone to bone, stabilize joints.

• Tendons: Connect muscle to bone, aid in movement and stability.

• Bursae: Fluid-filled sacs that reduce friction between tissues.

Types of Synovial Joints (by Movement)

Synovial joints are classified by the type and range of motion they allow:

Type of Joint	Movement	Example
Gliding (plane) joint	Gliding/slight non-axial	Intercarpal, intertarsal joints
Hinge joint	Angular, monoaxial (like a door hinge)	Knee, elbow, ankle, interphalangeal joints
Pivot joint	Rotational movement only	Proximal radioulnar joint, atlanto-axial joint
Condyloid (ellipsoid) joint	Angular, biaxial	Radiocarpal, metatarsophalangeal joints
Saddle joint	Biaxial movement	First carpometacarpal joint (thumb)
Ball-and-socket joint	Multiaxial movement	Shoulder, hip joints

Types of Movements at Synovial Joints

• Linear/gliding movements: Bones slide past each other.

• Angular movements: Change the angle between bones (e.g., flexion, extension, abduction, adduction).

• Circumduction: Circular movement combining flexion, extension, abduction, and adduction.

• Rotation: Bone turns around its own axis (e.g., internal and external rotation).

• Special movements: Include inversion/eversion (foot), dorsiflexion/plantar flexion (ankle), pronation/supination (forearm).

Range of Motion (ROM) refers to the extent of movement possible at a joint, determined by the joint structure and surrounding tissues.

Examples of Major Joints

Elbow Joint

• Complex hinge joint involving the humerus, radius, and ulna.

• Includes the large humeroulnar joint and smaller humeroradial joint.

• Stabilized by three main ligaments: radial collateral ligament, annular ligament, and ulnar collateral ligament.

• Muscles such as the biceps brachii allow for flexion and supination of the forearm.

Knee Joint

• Largest and most complex hinge joint in the body.

• Transfers weight from femur to tibia.

• Includes three articulations: between femoral condyles and tibial surface, and between patella and femur.

• Movements: flexion, extension, limited rotation.

• Stabilized by seven major ligaments: patellar ligament, two popliteal ligaments, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL).

• Contains menisci (medial and lateral) for shock absorption.

Shoulder Joint (Glenohumeral Joint)

• Ball-and-socket joint with the greatest range of motion.

• Head of the humerus articulates with the glenoid cavity of the scapula.

• Supported by the glenoid labrum, rotator cuff muscles, and five major ligaments (acromioclavicular, coracoclavicular, coraco-acromial, coracohumeral, glenohumeral).

Hip Joint

• Strong ball-and-socket joint.

• Head of the femur articulates with the acetabulum of the hip bone.

• Contains a horseshoe-shaped articular cartilage and acetabular labrum.

• Allows for flexion, extension, abduction, adduction, circumduction, and rotation.

• Stabilized by five main ligaments: iliofemoral, pubofemoral, ischiofemoral, transverse acetabular, and ligament of the femoral head.

• Surrounded by strong muscles for additional stability.

Vertebral Joints

• Joints between vertebrae (C2 to sacrum) are separated by intervertebral discs.

• Allow for flexion, extension, lateral flexion, and rotation.

• Special joint between C1 (atlas) and C2 (axis) allows for rotation of the head.

Age-Related Changes in Joints

• "Wear-and-tear" increases the risk of rheumatism and arthritis.

• Decreased range of motion with age.

• Increased risk of fractures due to changes in bone density.

• Nursing consideration: Osteoarthritis rates are higher in females than males.

Key Terms

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

• Synovial fluid: Viscous fluid within synovial joints for lubrication and nourishment.

• Ligament: Dense connective tissue connecting bone to bone.

• Tendon: Connective tissue connecting muscle to bone.

• Bursa: Fluid-filled sac reducing friction in joints.

• Meniscus: Crescent-shaped cartilage in certain joints (e.g., knee) for shock absorption.

Additional info: For a more comprehensive understanding, students should refer to diagrams of joint structures and practice identifying the components and types of movement at each major joint.