External landmarks and boundaries
On the skin of the anterior arm region, the biceps brachii (m. biceps brachii) and the epicondyles of the humerus (epicondylus medialis et lateralis) are well-contoured. Two sulci run along the edges of the biceps:
- Medial sulcus (sulcus bicipitalis medialis). It is of major clinical significance: the humerus is palpable here, and the brachial artery runs through it. This is precisely where a tourniquet is applied or the artery is digitally compressed during hemorrhage.
- Lateral sulcus (sulcus bicipitalis lateralis). Proximally, it continues into the deltopectoral sulcus (sulcus deltopectoralis).
Both sulci transition distally into the anterior cubital region.
Boundaries of the region:
- Superior: a line between the attachment points of the pectoralis major and latissimus dorsi muscles.
- Inferior: a circular line 4 cm proximal to the epicondyles.
- Lateral: vertical lines drawn upward from the epicondyles.
Layer-by-layer Structure
The layers of the anterior arm region have specific features that determine surgical approaches and the course of infections:
- Skin: thin (especially medially) and mobile. Innervated by the medial brachial cutaneous nerve (n. cutaneus brachii medialis).
- Subcutaneous adipose tissue: loose.
- Superficial fascia: poorly developed for the most part, condensing in the lower third to form sheaths for superficial structures.
- Deep fascia (fascia brachii): surrounds the entire arm as a dense sheath. In the medial sulcus at the border of the middle and lower thirds, it splits to form the Pirogov canal. The basilic vein (v. basilica) passes inward through it, while the medial antebrachial cutaneous nerve (n. cutaneus antebrachii medialis) emerges onto the surface.
From the deep fascia, medial and lateral intermuscular septa extend inward to the bone, dividing the arm into anterior and posterior fascial compartments.
Anterior fascial compartment
Anteriorly, the anterior compartment (compartimentum brachii anterius) is bounded by the deep fascia, and posteriorly by the humerus and intermuscular septa.
Muscles are arranged in two layers:
- Superficial layer: long head of the biceps brachii.
- Deep layer: in the upper third, the coracobrachialis muscle (m. coracobrachialis) and short head of the biceps; in the lower two thirds, the brachialis muscle (m. brachialis).
Main neurovascular bundle: Located within its own sheath formed by the medial intermuscular septum. In the upper third, it lies medial to m. coracobrachialis, and more inferiorly, along the medial margin of the biceps.
- Composition: brachial artery (a. brachialis), accompanying veins (vv. brachiales), and median nerve (n. medianus).
Topography in the upper third: Relative to the brachial artery, the structures are arranged as follows:
- Laterally: median nerve.
- Medially: ulnar nerve (n. ulnaris) and medial antebrachial cutaneous nerve (lying even more medially).
- Most superficially and internally: basilic vein (v. basilica).
Pathways of purulent process propagation
The loose connective tissue of the anterior fascial compartment of the arm communicates with adjacent regions, determining the migration pathways of purulent collections during suppuration:
- Proximally: pus can break through into the axillary fossa (fossa axillaris) along the main neurovascular bundle.
- Distally: infection can descend into the subcutaneous tissue of the anterior cubital region (regio cubitalis anterior).
- Into the posterior fascial compartment: purulent collections can spread along the course of the radial nerve (n. radialis).
- Into the subcutaneous tissue: breakthrough is possible through the opening in the fascia—the Pirogov canal.
Briefly: answers to topical questions
What branches does the brachial artery give off in the anterior arm region?
In the anterior arm region, the brachial artery gives off the profunda brachii artery and the superior ulnar collateral artery.
- Profunda brachii artery (a. profunda brachii) — arises in the upper third of the arm and passes with the radial nerve into the posterior fascial compartment.
- Superior ulnar collateral artery (a. collateralis ulnaris superior) — arises in the middle third of the arm and enters the posterior compartment along with the ulnar nerve.
How are the elements of the neurovascular bundle arranged relative to each other in the middle and lower thirds of the arm?
In the middle and lower thirds of the arm, the elements of the main neurovascular bundle change their mutual arrangement.
- Middle third of the arm — the median nerve (n. medianus) crosses the brachial artery (a. brachialis) anteriorly, passing to its medial side.
- Lower third of the arm — the median nerve is located 0.5–1.0 cm medial to the brachial artery.
Over this extent, the brachial artery itself projects along the medial margin of the biceps brachii muscle.
What innervates the skin of the anterior arm region?
The skin of the anterior arm region is innervated by branches of the medial brachial cutaneous nerve and has segmental innervation.
- Medial brachial cutaneous nerve (n. cutaneus brachii medialis) — branches out in the skin of the medial surface of the upper half of the arm.
- C5 segment — provides innervation to the lateral surface of the arm.
- Th2 segment — provides innervation to the medial surface of the arm.
What innervates the flexor muscles of the anterior group of the arm?
The flexor muscles of the anterior group of the arm are innervated by branches of the musculocutaneous nerve.
- Musculocutaneous nerve (n. musculocutaneus) — arises from the lateral cord of the brachial plexus and gives off branches to all anterior muscles of the arm.
The innervated muscles include the coracobrachialis muscle (m. coracobrachialis), biceps brachii muscle (m. biceps brachii), and brachialis muscle (m. brachialis).
Where exactly does the musculocutaneous nerve pass in the anterior arm region?
In the anterior arm region, the musculocutaneous nerve passes through the coracobrachialis muscle and lies within the anterior fascial compartment.
- Initial section — the nerve pierces the coracobrachialis muscle (m. coracobrachialis).
- Along the arm — courses directly within the anterior fascial compartment.
- Lower boundary — the terminal branch of the nerve emerges from under the biceps brachii muscle (m. biceps brachii), changing its name to the lateral antebrachial cutaneous nerve.
To remember the composition of the main neurovascular bundle, you can use the acronym VAN (Vein, Artery, Nerve) — here they are vv. brachiales, a. brachialis, and n. medianus.
Class and exam questions
Where is it most effective to compress the brachial artery to stop bleeding?
The artery should be compressed against the humerus along the medial bicipital sulcus (sulcus bicipitalis medialis).
Which nerves pass through the anterior fascial compartment of the arm throughout its entire length?
Throughout the anterior compartment, the median (n. medianus) and musculocutaneus (n. musculocutaneus) nerves pass. The ulnar and radial nerves leave the anterior compartment in the middle or upper parts.
What is Pirogov's canal in the arm?
This is a splitting of the brachial fascia in the medial sulcus (at the border of the middle and lower thirds). The basilic vein (v. basilica) dives into it, and the medial cutaneous nerve of the forearm emerges from it.
Does the median nerve give off branches in the arm?
No, the median nerve (n. medianus) passes through the anterior compartment of the arm in transit and gives off no branches here.
What else to study on this topic
- Topography of the neurovascular bundles in the middle and lower thirds of the arm
- Branching of the brachial artery (A. brachialis)
- Transition of the radial and ulnar nerves into the posterior fascial compartment
- Topography of superficial veins (v. basilica, v. cephalica)
- Topographical features of n. musculocutaneus near the cubital fossa
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