Posterior region of the forearm

Boundaries and External Landmarks

The following external landmarks are used to define the region: the lateral and medial epicondyles of the humerus (epicondylus lateralis et medialis), the border of the ulna, and the styloid processes of the radius and ulna.

• Superior boundary: a transverse line 4 cm below the epicondyles of the humerus.
• Inferior boundary: a transverse line 2 cm above the tip of the radial styloid process.
• Lateral boundaries: vertical lines from the epicondyles to the respective styloid processes, separating the posterior region from the anterior one.

Layer-by-layer Structure

1. Skin: mobile, hairy, and significantly thicker compared to the anterior region of the forearm.
2. Subcutaneous tissue: poorly developed. It contains a venous network (draining into v. cephalica and v. basilica) and cutaneous nerves (n. cutaneus antebrachii posterior, medialis et lateralis).
3. Fascia propria (Fascia propria): dense in the upper part, aponeurosis-like. Medially, it fuses with the ulna, and laterally, it gives off the posterior radial intermuscular septum, forming the posterior fascial compartment (Compartimentum antebrachii posterius).

Muscles of the posterior forearm region

The muscles are arranged in two layers and function to extend the wrist and fingers.

The superficial layer originates from the lateral epicondyle of the humerus (from the ulna to the radius):

• Extensor carpi ulnaris (m. extensor carpi ulnaris);
• Extensor digiti minimi (m. extensor digiti minimi);
• Extensor digitorum (m. extensor digitorum) — tendons extend to all digits except the thumb;
• Extensor carpi radialis brevis and longus (m. extensor carpi radialis brevis et longus).

The deep layer (originating primarily from the forearm bones and interosseous membrane):

• Extensor indicis (m. extensor indicis);
• Extensor pollicis longus (m. extensor pollicis longus);
• Extensor pollicis brevis (m. extensor pollicis brevis);
• Abductor pollicis longus (m. abductor pollicis longus);
• Supinator (m. supinator) — located in the upper lateral part.

Vessels and Nerves

A fascial space is located between the fascial layers of the superficial and deep muscle layers. The posterior neurovascular bundle runs through it:

• Deep branch of the radial nerve (r. profundus n. radialis): emerges from the supinator canal, innervating all muscles of the posterior and lateral compartments. Its continuation is the posterior interosseous nerve.
• Posterior interosseous artery (a. interossea posterior): emerges through the upper opening of the interosseous membrane, located medial to the nerve.

In the lower third of the forearm, the anterior interosseous artery (a. interossea anterior) also enters the compartment, playing an important role in collateral circulation.

Class and exam questions

What else to study on this topic

• Peculiarities of the deep layer tendon paths (tendon cross-over)
• Topography of the supinator canal
• Pirogov's (Parona's) space (on the anterior forearm, in the context of cross-sections)
• Collateral circulation of the forearm
• Topography of the superficial cutaneous nerves of the posterior forearm region

Other topics in the "Upper Extremity" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.