Bone Articulations and Joint Classification

• Articulations of bones are joints

Functions of Joints

• Hold bones together
• Allow for mobility
• Involve cartilage and ligaments

Joint Classification

• Classified structurally or functionally

Structural Classification

• Fibrous joints: Composed of fibrous connective tissue and are generally immovable
• Cartilaginous joints: Simple, immovable, or slightly moveable
• Synovial joints: Complex and freely moveable

Functional Classification

• Synarthroses: Immovable joints
• Amphiarthroses: Slightly moveable joints

Fibrous Joints

• No joint cavity
• Bones are held together by fibrous connective tissue
• Can absorb shock but permit little or no movement
• Interosseous membrane between radius & ulna or fibula & tibia (syndesmosis)
• Sutures – joints between skull bones
• Fibrous tissue connects roots of teeth to alveolar process (gomphosis)

Cartilaginous Joints

• No joint cavity.
• Bones are held together by cartilage.
• Can attenuate applied forces and permit some movement
  • Synchondroses: Contains hyaline cartilage
  • Symphyses: Intervertebral disc, Pubic symphysis- fibrocartilage

Synovial Joint

• Joint cavity that allows free movement
• Joint capsule that is fibrous
• Synovial membrane which attaches to margins of articular cartilage, secretes synovial fluid to reduce friction, provide nutrients, and facilitate phagocytic cells
• Articular cartilage is hyaline
• Meniscus(i) is fibrocartilage articular discs, such as in the knee joint and temporomandibular joint
• Ligaments are intracapsular and extracapsular and reinforce joint structures
• Bursae are flattened fibrous sacs filled with synovial fluid
• Tendon sheath is an elongated bursa that wraps around a tendon

Types of Movement in Synovial Joints

• Plane/Gliding Joints: Bone surfaces are flat or slightly curved, allowing side-to-side movement only and prevented from rotation by ligaments. Examples include intercarpal joints, intertarsal joints, and vertebrocostal joints.
• Pivot Joint: Rounded surface of bone articulates with ring formed by 2nd bone & ligament and allows rotation around longitudinal axis. Examples: Atlas C1 - axis C2 (atlanto-axial), proximal radio-ulnar joint
• Hinge Joints: Convex surface of one bone fits into concave surface of the 2nd bone, allowing uniaxial, limited movement (like a door hinge). Examples include the knee, elbow, ankle, and interphalangeal joints in fingers.
• Condyloid/Ellipsoidal Joint: Oval-shaped projection fits into an oval depression; both articular surfaces are oval for biaxial movement of flexion/extend or abduction/adduction. Example: wrist & metacarpophalangeal (knuckles) joints for digits 2 to 5.
• Saddle Joint: One bone is saddled-shaped, and the other bone fits into it, allowing biaxial circumduction (around), where opposition allows tip of thumb to touch tip of other fingers.
• Ball and Socket Joint: Ball fitting into a cuplike depression allowing multiaxial movements: flexion/extension, abduction/adduction, and rotation. Examples include the shoulder joint (glenohumeral joint) and hip joint (coaxal joint).

Developmental Aspects and Conditions of Joints

• By embryonic week 8, joints resemble adult joints
• Joint size, shape, and flexibility are modified by activity
• Full-range-of-motion exercise key to postponing joint problems
• Weight-lifting/ bearing together with too much stress (jumps etc.) may damage articular cartilage
• Over advancing years ligaments and tendons shorten and weaken
• Bursitis: Inflammation of bursa due to stress, overuse, or friction, especially in the shoulder or knee.
• Tendonitis: Inflammation of tendon sheaths, often due to injury or overuse
• Arthritis: Inflammatory or degenerative diseases of joints, with over 100 different types. Affects especially elderly.

This lesson covers bone articulations, joint functions, and classification. It discusses structural classifications like fibrous, cartilaginous, and synovial joints. Functional classifications such as synarthroses and amphiarthroses are also explained.