Muscles of the Posterior Compartment of the Forearm

Overview

• The posterior compartment of the forearm contains extensor muscles and is also known as the extensor compartment.
• These muscles are responsible for:
  • Extension at the wrist joint
  • Extension of the fingers and thumb
  • Supination of the forearm
• Innervation by the radial nerve.

Layers of Muscles

1. Superficial Layer
2. Deep Layer

Superficial Layer Muscles

• Total of 7 Muscles
• Extensor Retinaculum: A fibrous band holding tendons in place.

Muscles

1. Brachioradialis

   • Origin: Lateral supracondylar ridge of the humerus
   • Insertion: Lateral surface of the distal radius
   • Function: Accessory flexor of the elbow

2. Extensor Carpi Radialis Longus

   • Origin: Lateral supracondylar ridge
   • Insertion: Base of the second metacarpal
   • Function: Extends and abducts the wrist

3. Extensor Carpi Radialis Brevis

   • Origin: Lateral epicondyle
   • Insertion: Base of the third metacarpal
   • Function: Extends and abducts the wrist

4. Extensor Digitorum

   • Origin: Lateral epicondyle
   • Insertion: Bases of the middle and distal phalanges of fingers 2-5
   • Function: Extends the fingers and wrist

5. Extensor Digiti Minimi

   • Origin: Lateral epicondyle
   • Insertion: Extensor hood of the little finger
   • Function: Extends the little finger

6. Extensor Carpi Ulnaris

   • Origin: Lateral epicondyle
   • Insertion: Base of the fifth metacarpal
   • Function: Extends and adducts the wrist

7. Anconeus

   • Origin: Lateral epicondyle
   • Insertion: Posterior ulna and olecranon

Deep Layer Muscles

• Total of 5 Muscles
• Innervation: Posterior interosseous nerve (continuation of deep branch of radial nerve)

Muscles

1. Supinator

   • Function: Supinates the forearm
   • Structure: Two heads (superficial and deep)

2. Abductor Pollicis Longus

   • Function: Abducts the thumb at the carpometacarpal joint

3. Extensor Pollicis Brevis

   • Function: Extends the thumb at the metacarpophalangeal joint

4. Extensor Pollicis Longus

   • Function: Extends the thumb at the interphalangeal joint

5. Extensor Indicis

   • Function: Extends the index finger

Key Points

• All muscles in the posterior forearm compartment are extensors and are named logically based on their actions and locations.
• The tutorial covers the structure, origins, insertions, and functions of each muscle in the extensor compartment.

Conclusion

• Review the logical naming and functions to help remember the muscle actions and placements.