Elbow Anatomy & Movement

Main ideas / concepts

• The elbow joint, while appearing simple, is a complex structure that provides:

  • Forearm flexion and extension
  • Forearm rotation (especially pronation/supination) to enable hand positioning for grasping

• Elbow anatomy is organized into major categories:

  • Bones and joints
  • Ligaments
  • Muscles and tendons

• Elbow function depends on:

  • The articulations between three bones
  • Stability/support provided by ligaments
  • Movement control from specific muscles whose dominance changes with forearm/hand position

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Elbow bones and joints (what moves what)

Elbow is composed of three bones

• Humerus
• Ulna
• Radius

Each contributes to specific movements.

1) Humeroulnar joint (hinge-like flexion/extension)

• Components: articulation between the trochlea of the humerus and the corresponding surface of the ulna
• Primary function: flexion and extension of the elbow

2) Humeroradial joint (forearm rotation)

• Components: articulation between the capitulum of the humerus and the head of the radius
• Primary function: pronation and supination of the forearm

3) Proximal radioulnar joint (radius rotates around ulna)

• Location/components: just below the radial head; formed by the radial notch of the ulna and the head of the radius
• Primary function: allows rotation of the radius around the ulna
  • Facilitates supination and pronation

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Carrying angle (anatomical feature + clinical deviations)

• The elbow has a carrying angle (also called cubital angle)
• Defined as the angle between:
  • the humerus and the forearm axes when the arm is in standard position (palm facing forward)

Typical range: 5–15°

• Usually greater in females: 10–15°
• Usually lower in males: 5–10°

Deformities:

• Cubitus valgus: forearm deviates laterally by > 15°
• Cubitus varus: forearm deviates medially by < 5°

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Elbow ligaments (stability and limiting excessive motion)

Elbow stability relies on a ligament network that resists abnormal stresses and excessive movement.

Medial collateral ligament (MCL)

• Location: inner (medial) side of the elbow
• Structure: three bands
  • Anterior ligament band
  • Posterior ligament band
  • Transverse ligament band
• Main role: resists excessive valgus outward stress
• Injury note: common in activities like throwing

Lateral collateral ligament (LCL) / Radio-collateral ligament (RCL)

• Location: outer (lateral) side of the elbow
• Main role: stabilizes against varus (inward-opening) stress
  • Helps prevent the elbow from opening on the outer side
• Injury note: less frequent; can occur with trauma or dislocations

Annular ligament

• Role: encircles the radial head, holding it firmly within the radial notch of the ulna
• Function: allows smooth radius rotation during pronation and supination while maintaining stability

Interosseous membrane

• Location/role: between the radius and ulna
• Function: helps distribute loads from the radius to the ulna during weight-bearing on the upper limb
• Mechanics: fiber orientation supports efficient load transfer and balanced force distribution

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Elbow muscles and movement control

Elbow flexion (bending the elbow)

Four muscles are described with position-dependent dominance:

• Brachialis
  • Leads when the arm/forearm is pronated
• Brachioradialis
  • Becomes dominant when the hand is in a mid position
• Biceps brachii
  • Dominant when the arm is supinated
  • Acts as a primary supinator and contributes significantly to elbow flexion
• Pronator teres
  • Primarily assists pronation (turning palm downward)
  • Also contributes to elbow flexion

Elbow extension (straightening the elbow)

• Triceps brachii
  • Primary extensor/mover for elbow extension
• Anconeus
  • Although small, contributes to:
    • elbow extension
    • joint stability

Elbow pronation (turning palm downward)

• Pronator teres (primary lead)
• Pronator quadratus
  • Works with pronator teres to facilitate pronation

Elbow supination (turning palm upward)

• Biceps brachii
  • Major role in supination in addition to flexion
• Supinator
  • Assists biceps brachii in forearm supination

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