📝 STANDARD DESCRIPTION:
Arthrology = study of joints (articulations).
3 Types based on movement / structure:
1. Synarthrosis (Fibrous joint) — IMMOVABLE.
• Bones held by dense fibrous tissue.
• Examples: cranial sutures, gomphosis (tooth-socket).
2. Amphiarthrosis (Cartilaginous joint) — SLIGHTLY MOVABLE.
• Bones connected by cartilage.
• Synchondrosis (hyaline) — growth plate.
• Symphysis (fibrocartilage) — pelvic symphysis, intervertebral disc.
3. Diarthrosis (Synovial joint) — FREELY MOVABLE.
• True 'joints' as we use the word.
• Have synovial cavity + capsule + cartilage + ligaments + synovial fluid.
• Most joints in the body fall here.
📚 DETAILED DESCRIPTION:
JOINTS — STRUCTURAL & FUNCTIONAL CLASSIFICATION
Joints (articulations / arthroses) are unions between bones, cartilage, or teeth. They are classified BOTH structurally (what holds bones together) AND functionally (how much they move).
1. FIBROUS JOINTS (Synarthroses): No cavity. Bones united by dense fibrous tissue. Essentially IMMOVABLE.
• Sutures — between flat bones of skull (e.g., sagittal suture). Fuse with age (synostosis).
• Syndesmoses — bones connected by ligament/membrane (e.g., interosseous membrane between equine radius-ulna).
• Gomphoses — peg-and-socket joint of tooth in alveolus (held by periodontal ligament).
2. CARTILAGINOUS JOINTS (Amphiarthroses): Bones united by cartilage. Slight movement.
• Synchondrosis — hyaline cartilage union (e.g., epiphyseal growth plate). Temporary; ossifies at maturity.
• Symphysis — fibrocartilage union (e.g., pelvic symphysis, intervertebral disc, mandibular symphysis).
3. SYNOVIAL JOINTS (Diarthroses): The classic 'joint' — most freely movable. All have:
• A synovial cavity filled with synovial fluid.
• Articular (hyaline) cartilage on bone ends.
• A fibrous joint capsule (outer fibrous layer + inner synovial membrane).
• Ligaments — within or outside capsule.
• Some have menisci (stifle), articular discs (TMJ), or fat pads.
SYNOVIAL JOINT SUBTYPES (by shape & axes of motion):
• Plane / Gliding joint — flat surfaces; small gliding motion (intercarpal).
• Hinge joint (Ginglymus) — uniaxial, flexion-extension only (elbow, hock).
• Pivot joint (Trochoid) — rotation around long axis (atlanto-axial).
• Condylar joint — biaxial; oval condyle + concave surface (stifle).
• Saddle joint (Sellar) — concavo-convex; biaxial (interphalangeal in some).
• Ball-and-socket (Spheroidal) — multiaxial; rotation in all directions (hip, shoulder).
SYNOVIAL FLUID: Clear, viscous, egg-white-like fluid. Functions: lubricate, nourish cartilage, absorb shock, remove debris. Made by synovial membrane (B-cells); contains hyaluronic acid.
// COMPARATIVE ANALYSIS
| HORSE |
Stifle (femoro-patellar + femoro-tibial) and fetlock are the famously 'high-motion' synovial joints — most prone to lameness/arthritis. |
| DOG |
Hip and stifle often affected by hip dysplasia and cranial cruciate rupture. |
| BIRD |
Joints of synsacrum almost completely fused — limited mobility, gain in stability. |
CLINICAL RELEVANCE
Arthrocentesis: Aspiration of synovial fluid for diagnosis (bacterial, immune-mediated arthritis). Septic arthritis: Joint sepsis — fluid becomes turbid with neutrophils. Osteoarthritis: Cartilage degeneration; common in old dogs and high-performance horses.
