Ulnar Arteries

Overview

The ulnar artery is one of the two terminal branches of the brachial artery and is a major blood vessel of the forearm and hand. It supplies the medial (ulnar) aspect of the forearm and forms the main contributor to the superficial palmar arch in the hand. Along with its counterpart, the radial artery, it ensures rich collateral circulation to the upper limb, making it vital for perfusion, thermoregulation, and hand function.

Location

The ulnar artery originates at the level of the neck of the radius, typically in the cubital fossa, as a terminal branch of the brachial artery. It then travels:

• Medially down the forearm

• Deep to the pronator teres and flexor carpi ulnaris muscles

• Superficial near the wrist, lateral to the ulnar nerve

• Into the palm, where it forms the superficial palmar arch by anastomosing with a branch of the radial artery

It is accompanied by the ulnar vein and the ulnar nerve in the distal forearm and wrist.

Structure

The ulnar artery is a muscular artery composed of three wall layers:

• Tunica intima: Endothelial lining with internal elastic lamina

• Tunica media: Smooth muscle and elastic fibers that maintain vascular tone

• Tunica adventitia: Connective tissue with vasa vasorum and sympathetic nerve fibers

Key branches of the ulnar artery include:

• Anterior ulnar recurrent artery – ascends to the medial epicondyle of the humerus

• Posterior ulnar recurrent artery – also ascends medially, contributing to elbow anastomoses

• Common interosseous artery – short branch that splits into anterior and posterior interosseous arteries

• Palmar and dorsal carpal branches

Function

The ulnar artery has several essential functions:

• Supplies oxygenated blood to the medial and central forearm muscles and skin

• Forms the superficial palmar arch, providing blood to the majority of the fingers and palm

• Supports joint perfusion at the elbow and wrist via recurrent and collateral branches

Physiological Role(s)

The ulnar artery plays critical roles in upper limb circulation:

• Collateral blood flow: Contributes to extensive anastomotic networks at the elbow and wrist, ensuring perfusion even during compression or movement

• Thermoregulation: Superficial course near the wrist allows for heat exchange in response to environmental changes

• Support for dexterity: Adequate perfusion of the hand supports fine motor control, grip strength, and recovery from fatigue or injury

Clinical Significance

The ulnar artery is significant in various clinical contexts:

• Ulnar Artery Thrombosis or Occlusion: Can lead to hand ischemia, especially in cases where collateral flow from the radial artery is insufficient

• Allen's Test: A bedside test used to evaluate ulnar and radial artery patency before arterial blood sampling or cannulation. It determines whether the ulnar artery can sustain adequate perfusion if the radial artery is compromised

• Hypothenar Hammer Syndrome: Repetitive trauma (e.g., using the heel of the hand as a hammer) can cause ulnar artery damage and lead to thrombosis and digital ischemia

• Arterial Grafts: Less commonly than the radial artery, the ulnar artery may be used in coronary or peripheral bypass grafting

• Vascular Access: Arterial lines or cannulas are rarely placed in the ulnar artery due to its deeper and less accessible location compared to the radial artery

• Arteriovenous Malformations (AVMs) and Aneurysms: Although rare, aneurysmal dilatation or AVMs involving the ulnar artery can present as a pulsatile mass or cause distal ischemia

Imaging techniques such as Doppler ultrasound, CT angiography, and MR angiography are commonly used to evaluate ulnar artery patency, caliber, and flow. Early identification of ulnar artery pathology is crucial in preserving hand function and preventing complications.