Joint Anatomy: Classification and Structure

Complete anatomy of joints - fibrous, cartilaginous, and synovial joints. Synovial joint components, types of movement, and major joint anatomy (shoulder, elbow, hip, knee).

Skeletal System 4 min read
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Joints (articulations) are the sites where two or more bones meet. They provide mobility, stability, or both, and are classified by their structure and function.

Classification of Joints

Structural Classification

Type Connecting Tissue Movement Examples
Fibrous Dense connective tissue None (synarthrosis) or minimal Skull sutures, tibiofibular syndesmosis, gomphosis
Cartilaginous Cartilage None or slight (amphiarthrosis) Intervertebral discs, pubic symphysis, growth plates
Synovial Joint cavity with synovial fluid Free (diarthrosis) Most joints

Functional Classification

Class Movement Examples
Synarthrosis None (immovable) Skull sutures, gomphosis
Amphiarthrosis Slight (limited) Pubic symphysis, intervertebral discs
Diarthrosis Free movement Knee, shoulder, hip, elbow

Fibrous Joints

Type Structure Location
Suture Interlocking edges, thin connective tissue Skull (coronal, sagittal, lambdoid)
Syndesmosis Ligamentous connection (more distance than sutures) Distal tibiofibular, radioulnar interosseous membrane
Gomphosis Peg-in-socket, periodontal ligament Tooth in alveolus

Cartilaginous Joints

Type Cartilage Type Location
Synchondrosis Hyaline cartilage Growth plate (epiphyseal plate), costochondral junction, first sternocostal joint
Symphysis Fibrocartilage Pubic symphysis, intervertebral discs, manubriosternal joint

Synovial Joints

General Structure

Component Description Function
Joint capsule Fibrous connective tissue (continuous with periosteum) Encloses joint, provides stability
Synovial membrane Inner layer of capsule (areolar or fibrous) Secretes synovial fluid
Synovial fluid Ultrafiltrate of plasma + hyaluronic acid Lubrication, nutrient supply, shock absorption
Articular cartilage Hyaline cartilage (no perichondrium) Low-friction surface, shock absorption
Joint cavity Space containing synovial fluid Allows movement
Ligaments Dense connective tissue bands Stabilize joint, guide movement
Bursae Fluid-filled sacs (synovial lining) Reduce friction between structures
Tendon sheaths Synovial-lined tubes around tendons Reduce friction in confined spaces

Synovial Joint Types

Type Axes Movement Examples
Ball and socket 3 Flexion/extension, abduction/adduction, rotation, circumduction Shoulder, hip
Hinge 1 Flexion/extension Elbow (humeroulnar), knee, ankle (talocrural), interphalangeal
Pivot 1 Rotation Atlantoaxial (C1-C2), proximal radioulnar
Condylar (ellipsoid) 2 Flexion/extension, abduction/adduction (no rotation) Wrist (radiocarpal), metacarpophalangeal
Saddle 2 Flexion/extension, abduction/adduction, circumduction Carpometacarpal (thumb)
Plane (gliding) Multiple Sliding Intercarpal, intertarsal, facet joints, sacroiliac

Major Joints

Temporomandibular Joint (TMJ)

  • Type: Condylar (modified hinge)
  • Bones: Mandibular condyle + temporal bone (mandibular fossa, articular tubercle)
  • Articular disc: Fibrocartilage between bones
  • Movements: Depression, elevation, protraction, retraction, lateral deviation

Shoulder Joint (Glenohumeral)

  • Type: Ball and socket (most mobile, least stable)
  • Bones: Humerus (head) + scapula (glenoid cavity)
  • Glenoid labrum: Fibrocartilage rim (deepens socket)
  • Capsule: Loose, thin

Ligaments:

Ligament Location Function
Glenohumeral (superior, middle, inferior) Anterior capsule Anterior stability
Coracohumeral Coracoid to greater tubercle Superior stability
Transverse humeral Across intertubercular sulcus Holds biceps tendon

Rotator cuff tendons (dynamic stability):

Muscle Action
Supraspinatus Abduction (initiation)
Infraspinatus External rotation
Teres minor External rotation
Subscapularis Internal rotation

Bursae: Subacromial, subdeltoid, subcoracoid

Movements: Flexion (180°), extension (50°), abduction (180°), adduction (30°), internal rotation (90°), external rotation (90°), circumduction

Elbow Joint

  • Type: Hinge (humeroulnar) + pivot (radioulnar)
  • Bones: Humerus + ulna (trochlear), humerus + radius (capitulum)

Ligaments:

Ligament Function
Ulnar collateral (medial) Valgus stability
Radial collateral (lateral) Varus stability
Annular ligament Holds radial head in place

Movements: Flexion (145°), extension (0°), pronation (80°), supination (80°)

Wrist Joint (Radiocarpal)

  • Type: Condylar (ellipsoid)
  • Bones: Radius + scaphoid, lunate, triquetrum
  • Articular disc (triangular fibrocartilage complex): Distal radioulnar joint

Movements: Flexion (80°), extension (70°), radial deviation (20°), ulnar deviation (40°)

Hip Joint

  • Type: Ball and socket (stable, weight-bearing)
  • Bones: Femur (head) + acetabulum
  • Acetabular labrum: Fibrocartilage rim

Ligaments:

Ligament Location Function
Iliofemoral (Y ligament of Bigelow) Anterior (strongest) Prevents hyperextension
Pubofemoral Anteromedial Limits abduction, extension
Ischiofemoral Posterior Limits internal rotation, extension
Ligamentum teres (fovea capitis) Inside joint Blood supply to femoral head (small)

Movements: Flexion (120°), extension (15°), abduction (45°), adduction (25°), internal rotation (30°), external rotation (45°)

Knee Joint

  • Type: Modified hinge (hinge + rotation)
  • Bones: Femur + tibia (femoral condyles + tibial plateau), patellofemoral joint
  • Largest joint in the body

Menisci (C-shaped fibrocartilage):

Meniscus Shape Attachments
Medial C-shaped Attached to MCL (more commonly torn)
Lateral O-shaped (nearly circular) Isolated (less commonly torn)

Ligaments:

Ligament Location Function
Anterior cruciate (ACL) Intracapsular Prevents anterior tibial translation
Posterior cruciate (PCL) Intracapsular Prevents posterior tibial translation
Medial collateral (MCL) Medial (extra-articular) Valgus stability
Lateral collateral (LCL) Lateral (extra-articular) Varus stability

Extensor mechanism:

  • Quadriceps tendon → patella → patellar tendon → tibial tuberosity

Bursae: Suprapatellar, prepatellar, infrapatellar (superficial and deep)

Capsule: Thin, strengthened by surrounding tendons/ligaments

Movements: Flexion (140°), extension (0°), internal rotation (10-15°), external rotation (10-15°)

Ankle Joint (Talocrural)

  • Type: Hinge
  • Bones: Tibia (medial malleolus), fibula (lateral malleolus), talus (trochlea)

Ligaments:

Ligament Region
Deltoid (medial) Medial (strong, triangular)
Anterior talofibular Lateral (most commonly sprained)
Calcaneofibular Lateral
Posterior talofibular Lateral

Movements: Dorsiflexion (20°), plantarflexion (40°)