Elbow

1. Anatomy of the Elbow Complex

Bones

The elbow is made of three bones:

  • Humerus – upper-arm bone

  • Ulna – medial forearm bone (pinky-side)

  • Radius – lateral forearm bone (thumb-side)

Joints

The elbow complex includes three functional joints:

  1. Humeroulnar Joint

    • Between the trochlea (humerus) and the trochlear notch (ulna)

    • Main role: Flexion/extension

  2. Humeroradial Joint

    • Between capitulum (humerus) and radial head

    • Role: Flexion/extension and helps with rotation stability

  3. Proximal Radioulnar Joint

    • Between radial head and radial notch of ulna

    • Main role: Supination/pronation

Ligaments

  • UCL (Ulnar Collateral Ligament)

    • Stabilizes valgus force (throwing motions)

    • Most commonly injured in overhead athletes

  • RCL (Radial Collateral Ligament)

    • Stabilizes varus forces

  • Annular Ligament

    • Wraps around the radial head

    • Allows smooth forearm rotation

2. Major Muscles Acting on the Elbow

Elbow Flexors

Muscle

Action

Notes

Biceps Brachii

Flexion & Supination

Most active when forearm is supinated

Brachialis

Primary flexor

Works in all forearm positions

Brachioradialis

Flexion

Strongest in neutral grip (hammer curl)

Elbow Extensors

Muscle

Action

Notes

Triceps Brachii

Primary extensor

Long head crosses shoulder joint

Anconeus

Assists extension

Helps stabilize elbow

Forearm Supinators

  • Biceps Brachii – most powerful

  • Supinator – works in neutral/extended positions

Forearm Pronators

  • Pronator Teres – pronation + weak elbow flexion

  • Pronator Quadratus – primary pronator, especially at end-range

3. Joint Movements at the Elbow

A. Flexion

  • Muscles: Biceps brachii, brachialis, brachioradialis

  • Typical ROM: ~140–150°

  • Functional examples: Lifting, pulling, curls

B. Extension

  • Muscles: Triceps, anconeus

  • ROM: ~0° (some people have slight hyperextension)

  • Functional examples: Pushing, throwing, dips

C. Supination

  • Muscles: Biceps brachii, supinator

  • Examples: Turning a doorknob, catching a ball with open hand

D. Pronation

  • Muscles: Pronator teres, pronator quadratus

  • Examples: Typing, dribbling a basketball, using a screwdriver

4. Injury Considerations

1. UCL Sprain / Tear ("Tommy John" injury)

Cause:

  • Repetitive valgus stress (e.g., pitching, overhead sports)

Symptoms:

  • Medial elbow pain

  • Loss of throwing velocity

  • Instability or “giving out” feeling

Related anatomy:

  • UCL, flexor-pronator group often overworked trying to stabilize

2. Lateral Epicondylitis (Tennis Elbow)

Cause:

  • Overuse of wrist extensors, especially ECRB

Symptoms:

  • Pain on lateral elbow

  • Difficulty gripping or lifting

Mechanics link:

  • Repetitive wrist extension + gripping

  • Poor shoulder or wrist mechanics increases strain

3. Medial Epicondylitis (Golfer’s Elbow)

Cause:

  • Overuse of wrist flexors or pronator teres

Symptoms:

  • Medial elbow pain

  • Pain with wrist flexion or pronation

4. Radial Head Subluxation (“Nursemaid’s elbow”)

Cause:

  • Sudden traction on a child’s arm

  • Movement of radial head under annular ligament

5. Biceps Tendon Rupture

Cause:

  • Forceful load during flexion or supination

  • Often seen in lifting or catching heavy weight awkwardly

Symptoms:

  • “Pop,” bruising, weakness in supination/flexion

6. Olecranon Bursitis

Cause:

  • Prolonged leaning on elbow, trauma, or infection

Symptoms:

  • Swelling over posterior elbow