Projection lines of neurovascular bundles
The landmark for the main neurovascular bundle is the line connecting the point between the anterior and middle thirds of the upper boundary of the region and the midpoint of the cubital crease. The latter point is located 1 cm medial to the tendon of the biceps brachii muscle (m. biceps brachii). This line corresponds to the medial bicipital sulcus (sulcus bicipitalis medialis). The basilic vein (v. basilica) is projected along this same axis.
The ulnar nerve (n. ulnaris) follows the course of the main bundle in the upper third, and below shifts medially, heading towards a point 1 cm lateral to the apex of the medial epicondyle.
The radial nerve (n. radialis) is projected onto the anterior surface only in the lower third of the arm, following the lateral sulcus (sulcus bicipitalis lateralis).
Vascular topography
The main vessel is the brachial artery (a. brachialis). Along its course, it gives off several important branches:
- In the upper third, a large deep artery of the arm (a. profunda brachii) branches off and immediately passes into the posterior fascial compartment.
- At the border of the upper and middle thirds, the superior ulnar collateral artery (a. collateralis ulnaris superior) originates, accompanying the ulnar nerve.
- In the lower third, the inferior ulnar collateral artery (a. collateralis ulnaris inferior) is formed. It descends along the brachialis muscle medially, participating in the formation of the ulnar collateral network.
The key veins of the region are the deep brachial vein (v. brachiales), as well as the superficial cephalic (v. cephalica) and basilic (v. basilica) veins.
Mutual arrangement of nerves and vessels by levels
The relationship of the nerve trunks to the brachial artery changes along the length of the arm.
In the middle third of the arm, significant rearrangements take place:
- The median nerve (n. medianus) lies anterior to the artery.
- The ulnar nerve (n. ulnaris) shifts medially, pierces the medial intermuscular septum, and leaves the anterior compartment, passing posteriorly.
- The medial antebrachial cutaneous nerve (n. cutaneus antebrachii medialis) is concealed within Pirogov's canal (a fascial splitting).
- The musculocutaneous nerve (n. musculocutaneus) runs obliquely outward between the biceps and brachialis muscles.
In the lower third of the arm:
- The median nerve lies medial to the brachial artery.
- The radial nerve (n. radialis), piercing the lateral intermuscular septum, returns to the anterior compartment and lies deep between the brachialis muscle and the lateral head of the triceps, joining the radial collateral artery.
Course of the musculocutaneous and radial nerves
The musculocutaneous nerve (n. musculocutaneus) penetrates through the coracobrachialis muscle (m. coracobrachialis) from the axillary fossa. Having emerged laterally, it conceals itself under the long head of the biceps. By the middle third of the arm, it lies on the deep fascia superficial to the brachialis muscle, providing innervation to all muscles of the anterior compartment.
The radial nerve (n. radialis) begins below the tendon of the latissimus dorsi, lying posterior to the artery. It almost immediately leaves the anterior compartment, passing into the posterior space between the long and lateral heads of the triceps brachii muscle (m. triceps brachii).
Briefly: answers to topical questions
What branches does the brachial artery give off in the arm?
In the upper third of the arm, the artery gives off a large branch—the deep artery of the arm (a. profunda brachii). At the border of the upper and middle thirds of the arm, the superior ulnar collateral artery (a. collateralis ulnaris superior) branches off. In the lower third of the arm, the inferior ulnar collateral artery (a. collateralis ulnaris inferior) branches off from the brachial artery; it runs obliquely downward along the surface of the brachialis muscle into the cubital region and participates in the formation of the ulnar collateral network.
How does the syntopy of the median nerve in relation to the brachial artery change along the arm?
- Upper third — the median nerve (n. medianus) is located lateral to the artery.
- Middle third — located anterior to the brachial artery, crossing it.
- Lower third — located medial to the brachial artery, but close to it.
Which specific muscles does the musculocutaneous nerve innervate in the arm?
The musculocutaneous nerve (n. musculocutaneus) innervates the muscles of the anterior fascial compartment of the arm: the biceps brachii muscle (m. biceps brachii), the coracobrachialis muscle (m. coracobrachialis), and the brachialis muscle (m. brachialis). On its way from the axillary fossa, it pierces the coracobrachialis muscle.
How many deep veins accompany the brachial artery?
The brachial artery is accompanied throughout its length by two brachial veins (vv. brachiales). Deep veins are venae comitantes and accompany arteries in pairs (two veins per one artery).
The median nerve crosses the artery like the letter "X" (from top to bottom, from outside in): in the upper third — laterally, in the middle — anteriorly, in the lower — medially.
Class and exam questions
With which structure does the ulnar nerve leave the anterior compartment of the arm?
The ulnar nerve passes into the posterior fascial compartment together with the superior ulnar collateral artery (a. collateralis ulnaris superior).
Where is Pirogov's canal located and what passes through it?
Pirogov's canal is a splitting of the deep fascia in the middle third of the arm. The basilic vein exits and the medial antebrachial cutaneous nerve enters through it.
In which third of the arm is the radial nerve projected anteriorly?
The radial nerve is projected onto the anterior surface only in the lower third of the arm, following the lateral sulcus.
What else to study on this topic
- Formation and Topography of Pirogov's Canal
- Syntopy of the Elements of the Main Neurovascular Bundle
- Topography of the Radial Nerve in the Lower Portions
- Anastomoses of the Ulnar Collateral Network
- Innervation of the Anterior Fascial Compartment
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