The Elbow & Radioulnar Joints

elbow inferior radioulnar joint radioulnar joint superior radioulnar joint ulnar collateral ligament

The Elbow

  • The elbow is a complex joint made up of the humerus articulating with the ulna (ulnohumeral joint) and the radius (radiohumeral joint)
  • Typical synovial, hinge joint allowing only uniaxial movement and reinforced by strong set of collateral ligaments
  • Note carrying angle: 10-15° in males, 20-25° in females 

Articular Surfaces

  • Articular surfaces on the humerus are the trochlea (anterior and posterior) and capitulum (anterior only)
  • Ulnar - trochlea notch formed by the coronoid and olecranon processes
  • Radius - biconcave superior aspect of head of radius
  • All covered with hyaline cartilage


  • Covered by a fibrous capsule that encloses the superior radio-ulnar joint
  • Attaches superiorly above the olecranon, radial and coronoid fossae and inferiorly blends with the annular ligament, to the neck of the radius and margins of the coronoid process
  • Medially and laterally is thickest and reinforced by the radial and ulnar collateral ligaments

Synovial Membrane

  • Very extensive - extends from the margin of the articular surface of the humerus, lines the coronoid, radial and olecranon fossæ (prone to impingement)
  • Lines deep surface of capsule
  • Attaches to articular margins of the ulna, annular ligament and radius
  • Fat pads within fossae protect bony elements in extension

Radial Collateral Ligament

  • Supported by a strong set of collateral ligaments
  • Lateral (radial) collateral ligament - smaller of the 2
    • From lateral epicondyle
    • To annular ligament
    • Limits adduction of forearm and extension

Ulnar Collateral Ligament

  • Stronger - formed from 3 (occasionally 4) bands
  • Anterior band - from medial epicondyle to medial coronoid process
  • Posterior band - from medial epicondyle to medial olecranon
  • Transverse (oblique) band - unites the distal attachments of the anterior and posterior bands

Movements & Surface Markings of the Elbow Joint

  • Physiological movements possible at the elbow are flexion/extension
  • Abduction / Adduction are limited by the collateral ligaments
  • Surface makings can be identified by drawing a line from a point 2 cm below the medial epicondyle to a point 1cm below the lateral epicondyle

Function & Stability

  • The joint is very stable due to: 
    • Good congruence between the joint surfaces
    • Collateral ligaments
    • Muscles surrounding the joints at certain angles
    • Max stability at 90 flexion due to muscle activation and maximum bony contact
  • Cubital fossa - area in the anterior elbow for venopuncture median nerve - brachial artery - radial nerve


  • Dislocation in children predominantly
  • Supracondylar, olecranon and radial head fractures most common
  • Medial joint damage due to a traumatic abduction force or repetitive strain

Superior Radioulnar Joint

  • Classified as a synovial pivot joint 
  • Between the circumference of the head of the radius and the radial notch on the ulna (covered in hyaline cartilage)
  • The inner surface of the annular ligament - attaches to anterior and posterior margins of radial notch - lined with fibrocartilage

Superior Radioulnar Joint

  • Common joint cavity and capsule with elbow
  • Stability is via the annular ligament, the quadrate ligament (from neck of radius to below radial notch) and the interosseous membrane

Inferior Radioulnar Joint

  • Also classified as a synovial pivot joint
  • Between head of ulna and ulnar notch on lower end of radius - both covered with hyaline cartilage
  • United by a loose capsule 
  • Stabilised by anterior and posterior thickenings in the capsule, interosseous membrane and the articular  disc (from base of ulnar styloid to distal edge of ulnar notch)

Interosseous Membrane

  • Very strong fibrous membrane that passes from the interosseous border on the ulna to the interosseous border on the radius
  • Fibres pass obliquely downwards and medially
  • Note oblique cord
  • Functions
    • Stabilises 2 bones of forearm/limits movement
    • Allow transmission of force from large lower end of radius to large upper end of ulna
    • Compartmentalises
    • Provides openings for passage of vessels and nerve from anterior to posterior  
    • Provides increased surface area for attachment of muscle

Radioulnar Articulations

  • Superior and inferior RU joints are palpable beneath the skin
  • All 3 articulations allow the movements of supination and pronation

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