Ulnar Artery

Introduction

Introduction to the Ulnar Artery in the Forearm

The ulnar artery is the larger of the two terminal branches of the brachial artery and is the principal medial arterial channel of the forearm. It supplies the medial aspect of the forearm muscles, forms the superficial palmar arch of the hand, and provides critical collateral circulation to the elbow. Its course, deep to the pronator teres and flexor digitorum superficialis, and its relationship to the ulnar nerve in the distal forearm make it an essential structure in reconstructive surgery, arterial bypass, and the evaluation of hand perfusion.

This module covers the origin, course, relations, branches, variations, and clinical applications of the ulnar artery in the forearm.

Study

1. Origin and Termination

The ulnar artery arises from the brachial artery in the cubital fossa, opposite the neck of the radius, approximately 1 cm distal to the elbow crease. It is the larger terminal branch, deviating medially while the radial artery continues laterally. The ulnar artery terminates in the hand as the superficial palmar arch, which is completed by the superficial palmar branch of the radial artery.

2. Course and Relations in the Forearm

From its origin, the ulnar artery passes deep to the pronator teres, then continues distally under the fibrous arch of the flexor digitorum superficialis (FDS). It runs on the flexor digitorum profundus (FDP) muscle, with the median nerve initially lateral and then crossing superficial to it from lateral to medial.

In the distal forearm, the ulnar artery becomes superficial, emerging lateral to the flexor carpi ulnaris tendon and medial to the FDS tendons. The ulnar nerve lies medial to the artery in the distal third, and both pass into the hand through the ulnar tunnel (Guyon’s canal), where the artery is lateral to the nerve and the pisiform bone.

Unlike the radial artery, the ulnar artery does not wind around the wrist; it passes directly into the palm superficial to the flexor retinaculum, lateral to the pisiform.

3. Branches in the Forearm

The ulnar artery gives several named branches within the forearm:

Anterior ulnar recurrent artery: Arises just distal to the origin, ascends between brachialis and pronator teres, and anastomoses with the inferior ulnar collateral artery from the brachial artery, contributing to the cubital anastomosis.

Posterior ulnar recurrent artery: Arises slightly distal to the anterior recurrent, passes posteriorly between the flexor digitorum profundus and flexor carpi ulnaris, and anastomoses with the superior ulnar collateral artery.

Common interosseous artery: A short, thick branch that arises from the ulnar artery just distal to the radial tuberosity. It quickly divides into the anterior interosseous artery (which runs with the anterior interosseous nerve) and the posterior interosseous artery (which runs with the posterior interosseous nerve). The common interosseous also gives off the small median artery (which may persist into the hand in some individuals).

Muscular branches: Numerous small vessels supply the medial forearm muscles, including flexor carpi ulnaris, flexor digitorum profundus (medial half), and flexor digitorum superficialis.

Palmar carpal branch: A small vessel that arises near the distal border of pronator quadratus, runs laterally, and anastomoses with the palmar carpal branch of the radial artery and the anterior interosseous artery to form the palmar carpal arch.

Dorsal carpal branch: Arises just before the ulnar artery enters the palm. It passes medially, deep to the flexor carpi ulnaris tendon, and anastomoses with the dorsal carpal branch of the radial artery and the anterior interosseous artery to form the dorsal carpal arch.

The ulnar artery then enters the hand, giving off the deep palmar branch and continuing as the superficial palmar arch.

4. Anatomical Variations

The ulnar artery may arise from the brachial artery higher than usual (high origin) or even from the axillary artery. Its course may be superficial to the FDS, making it more prone to injury. The common interosseous artery occasionally arises directly from the brachial artery or radial artery. The superficial palmar arch may be incomplete in up to 20% of individuals, altering digital perfusion patterns.

5. Clinical Relevance

Ulnar artery pulse: Palpable lateral to the pisiform bone at the wrist, though often more difficult to feel than the radial pulse.

Allen’s test: Evaluates ulnar artery patency and collateral circulation before radial artery cannulation or harvest.

Hypothenar hammer syndrome: Thrombosis or aneurysm of the distal ulnar artery due to repetitive trauma over the hook of hamate, leading to digital ischemia.

Ulnar artery flap: The ulnar artery and its perforating branches are used in reconstructive microsurgery (e.g., free flap for oral reconstruction) because of its consistent anatomy and expendability (provided a patent palmar arch and radial artery exist).

Intra‑arterial injection: Accidental injection into the ulnar artery at the wrist can cause thrombosis and extensive hand ischemia due to end‑artery effects if collateral circulation is insufficient.

Summary

Summary of the Ulnar Artery in the Forearm

The ulnar artery is the main medial artery of the forearm, supplying the deep and superficial flexor muscles via the common interosseous and muscular branches. It forms the superficial palmar arch, the dominant supply to the digital arteries. Its deep course under pronator teres and FDS, and its superficial termination in Guyon’s canal, makes it vulnerable to trauma at the wrist. The ulnar artery is a critical component of hand perfusion and a valuable tool in microvascular reconstruction.