Antebrachial region (with transverse section)
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From WikiLectures

The *Antebrachial Region*


Bones of the Antebrachial Region:

1. *Radius*:

  - Located on the lateral side (thumb side) of the forearm.

  - Its proximal end articulates with the humerus at the elbow and the ulna at the proximal radioulnar joint.

  - Its distal end articulates with the carpal bones at the wrist joint and the ulna at the distal radioulnar joint.


2. *Ulna*:

  - Located on the medial side (little finger side) of the forearm.

  - Proximally, it articulates with the humerus at the elbow (via the olecranon process) and the radius.

  - Distally, it is connected to the radius but does not directly articulate with the carpal bones of the wrist.


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### *Muscles of the Antebrachial Region:

The forearm muscles are divided into *anterior (flexor) and posterior (extensor) compartments*, separated by the interosseous membrane and fascia.


Anterior Compartment (Flexors and Pronators):

- Superficial Layer:

  1. *Pronator teres*: Pronates the forearm and assists in flexing the elbow.

  2. *Flexor carpi radialis*: Flexes and abducts the wrist.

  3. *Palmaris longus*: Flexes the wrist (often absent in some individuals).

  4. *Flexor carpi ulnaris*: Flexes and adducts the wrist.


- Intermediate Layer:

  1. *Flexor digitorum superficialis*: Flexes the middle phalanges of the fingers and aids in wrist flexion.


- Deep Layer:

  1. *Flexor digitorum profundus*: Flexes the distal phalanges of the fingers.

  2. *Flexor pollicis longus*: Flexes the thumb.

  3. *Pronator quadratus*: Pronates the forearm.


Posterior Compartment (Extensors and Supinators):

- *Superficial Layer*:

  1. *Brachioradialis*: Flexes the forearm at the elbow.

  2. *Extensor carpi radialis longus*: Extends and abducts the wrist.

  3. *Extensor carpi radialis brevis*: Extends and abducts the wrist.

  4. *Extensor digitorum*: Extends the fingers.

  5. *Extensor digiti minimi*: Extends the little finger.

  6. *Extensor carpi ulnaris*: Extends and adducts the wrist.


- Deep Layer:

  1. *Supinator*: Supinates the forearm.

  2. *Abductor pollicis longus*: Abducts the thumb.

  3. *Extensor pollicis brevis*: Extends the thumb at the metacarpophalangeal joint.

  4. *Extensor pollicis longus*: Extends the thumb at the interphalangeal joint.

  5. *Extensor indicis*: Extends the index finger.


Blood Supply:

1. *Brachial artery: Divides into the **radial* and *ulnar arteries* just below the elbow.

  - *Radial artery*: Runs along the lateral side of the forearm (near the radius) and supplies the lateral forearm muscles.

  - *Ulnar artery*: Runs along the medial side of the forearm (near the ulna) and supplies the medial forearm muscles.

  - *Anterior and posterior interosseous arteries*: Branches of the ulnar artery that supply deeper structures in the forearm.


*Nerve Supply:*

1. *Median nerve*:

  - Innervates most of the flexor muscles in the forearm (except for flexor carpi ulnaris and the medial part of flexor digitorum profundus).

  - Also provides sensory innervation to the lateral palm and first three fingers.


2. *Ulnar nerve*:

  - Innervates the flexor carpi ulnaris and the medial half of the flexor digitorum profundus.

  - Provides sensory innervation to the medial palm and the fourth and fifth fingers.


3. *Radial nerve*:

  - Supplies all the extensor muscles in the posterior compartment of the forearm.

  - Provides sensory innervation to the dorsum of the hand and part of the forearm.


Borders and Clinical Projections*:

- *Proximal boundary: Begins at the **cubital fossa*, the anterior elbow depression, bordered by the brachioradialis and pronator teres muscles.

- *Distal boundary*: Ends at the wrist joint.

- *Medial and lateral borders*: The medial border is marked by the ulna, and the lateral border by the radius.

 

Clinical Relevance:*

- *Fractures: Commonly occur in both the **radius* and *ulna, such as **Colles’ fracture* of the distal radius.

- *Compartment Syndrome*: Increased pressure in the forearm's fascial compartments can lead to tissue ischemia.

- *Tennis Elbow (Lateral Epicondylitis)*: Affects the common extensor tendon at the lateral epicondyle.

- *Golfer’s Elbow (Medial Epicondylitis)*: Affects the common flexor tendon at the medial epicondyle.