(Ch 8 lecture) Joint Structure and Types

Overview

This lecture covers the structure, classification, and function of joints (articulations), including details of joint types, movement, and major synovial joints and their features.

Introduction to Joints

• A joint (articulation) is where two bones meet.
• Arthrology is the study of joint structure, function, and dysfunction.
• Biomechanics and kinesiology study movement and musculoskeletal function.
• Joints are the weakest part of the skeleton but can withstand various forces.
• Joints provide mobility and hold the skeleton together.

Classification of Joints

• Joints are classified by function (movement) and structure (binding material and cavity).
• Functional classes: synarthrosis (immovable, axial skeleton), amphiarthrosis (slightly movable, axial skeleton), diarthrosis (freely movable, limbs).
• Structural classes: fibrous (immovable, no cavity), cartilaginous (rigid/slightly movable, no cavity), synovial (freely movable, fluid cavity).

Fibrous Joints

• Bones joined by dense fibrous connective tissue, no joint cavity.
• Types:
  • Sutures (skull; serrate, lap, plane types)
  • Syndesmoses (bones connected by ligaments; e.g., distal tibiofibular joint)
  • Gomphoses (peg-in-socket, e.g., tooth in socket held by periodontal ligament)

Cartilaginous Joints

• Articulating bones united by cartilage, no joint cavity, not highly movable.
• Synchondroses: joined by hyaline cartilage (e.g., epiphyseal plate, rib 1 to manubrium), immovable.
• Symphyses: bones covered with hyaline cartilage fused to fibrocartilage pad (e.g., intervertebral discs, pubic symphysis), slightly movable.

Synovial Joints and Features

• Bones separated by fluid-filled cavity, most freely movable and complex joints.
• Key features:
  • Articular cartilage (hyaline, covers bone ends, absorbs compression)
  • Joint cavity (contains synovial fluid)
  • Articular capsule (2 layers: fibrous and synovial membrane)
  • Synovial fluid (lubricates joint)
  • Reinforcing ligaments (stabilize joint)
  • Articular discs (fibrocartilage pads between bones)

Movements at Synovial Joints

• Muscles attach to bones at origin (immovable) and insertion (movable).
• Joint movement types:
  • Gliding: flat bones slide past each other (e.g., wrist)
  • Angular: changes angle between bones (flexion, extension, hyperextension, abduction, adduction, circumduction, rotation)
  • Special: supination, pronation (forearm); inversion, eversion (foot); protraction, retraction; elevation, depression; opposition (thumb).

Range of Motion of Synovial Joints

• Nonaxial: gliding only.
• Uniaxial: movement in one plane.
• Biaxial: movement in two planes.
• Multiaxial: movement in all three planes.

Types of Synovial Joints

• Plane: nonaxial, flat surfaces (e.g., intercarpal)
• Hinge: uniaxial, cylindrical to trough (e.g., elbow)
• Pivot: uniaxial, rounded to ring (e.g., radioulnar, atlas-axis)
• Condyloid: biaxial, oval surfaces (e.g., metacarpophalangeal)
• Saddle: biaxial, concave/convex regions (e.g., thumb)
• Ball-and-Socket: multiaxial, spherical head fits into socket (e.g., shoulder, hip)

Major Synovial Joints

• Temporomandibular (jaw): mandible and temporal bone; has lateral ligament.
• Shoulder (glenohumeral): humerus and scapula; glenohumeral, coracoacromial, and coracohumeral ligaments provide support.
• Elbow: humerus, radius, ulna; annular, radial collateral, and ulnar collateral ligaments.
• Hip (coxal): femur and acetabulum; iliofemoral, ischiofemoral, pubofemoral, and ligamentum teres.
• Knee: femur, tibia, patella; patellar, fibular/tibial collateral, ACL, PCL, menisci; susceptible to injury (unhappy triad: tibial collateral, medial meniscus, ACL tears).

Key Terms & Definitions

• Joint/Articulation — point where two bones meet.
• Arthrology — study of joints.
• Synarthrosis — immovable joint.
• Amphiarthrosis — slightly movable joint.
• Diarthrosis — freely movable joint.
• Synovial fluid — lubricant in synovial joints.
• Articular cartilage — hyaline cartilage covering bone ends.
• Meniscus — fibrocartilage pad in joints.

Action Items / Next Steps

• Read textbook sections on the six synovial joint features for detailed understanding.
• Review Chapter 1 content on planes of movement.
• Study diagrams of major synovial joints and their ligaments.