Ulnar artery

The ulnar artery is one of the major blood vessels of the forearm and hand, responsible for supplying oxygenated blood to the medial aspect of the forearm, wrist, and hand. It is a terminal branch of the brachial artery, with the radial artery being its counterpart on the lateral side of the forearm. The ulnar artery contributes significantly to the vascular supply of the hand, particularly through the formation of the superficial palmar arch.

Location

The ulnar artery is located on the medial (ulnar) side of the forearm. It originates from the brachial artery in the cubital fossa, just below the elbow, and travels down the forearm between the flexor muscles, specifically between the flexor carpi ulnaris and the flexor digitorum profundus. It runs parallel to the ulnar nerve. As it reaches the wrist, the ulnar artery passes through the Guyon’s canal and enters the hand, where it plays a major role in forming the superficial palmar arch.

Structure and Anatomy

The ulnar artery is a major blood vessel that travels along the medial aspect of the forearm and contributes significantly to the blood supply of the hand. Its anatomy includes its origin, course, branches, and its relationship to surrounding structures, all of which are important to understand its detailed pathway.

Origin

The ulnar artery arises as one of the two terminal branches of the brachial artery, the other being the radial artery. This bifurcation occurs at the level of the cubital fossa, which is the triangular area on the anterior aspect of the elbow. The ulnar artery emerges from the brachial artery just below the elbow joint, typically at or slightly below the radial head, where the brachial artery divides into the radial and ulnar arteries.

Course

The course of the ulnar artery is divided into several regions as it descends through the forearm and enters the hand:

Proximal Forearm

In the upper forearm, the ulnar artery travels deep, running between the flexor muscles. It is positioned medially and lies deep to the pronator teres and the flexor digitorum superficialis muscles. The artery is closely related to the median nerve at this point, though they soon separate.

Mid Forearm

As the ulnar artery continues down the forearm, it lies between the flexor carpi ulnaris muscle and the flexor digitorum profundus muscle. This position provides protection to the artery as it travels down the forearm. During this portion of its course, the ulnar artery runs alongside the ulnar nerve, with the artery located lateral to the nerve.

Distal Forearm and Wrist

In the distal forearm, near the wrist, the ulnar artery becomes more superficial. It lies between the tendons of the flexor carpi ulnaris and the flexor digitorum superficialis muscles. As it approaches the wrist, the ulnar artery enters the Guyon’s canal, a fibro-osseous tunnel located on the medial aspect of the wrist, through which both the ulnar artery and ulnar nerve pass to enter the hand.

Branches

The ulnar artery gives rise to several important branches as it descends through the forearm and hand. These branches supply different regions of the forearm, wrist, and hand:

Anterior Ulnar Recurrent Artery

This branch arises near the origin of the ulnar artery and ascends toward the elbow to participate in the anastomosis around the elbow joint, contributing to the vascular network that supplies the joint.

Posterior Ulnar Recurrent Artery

Similar to the anterior ulnar recurrent artery, this branch ascends posteriorly to the elbow joint, where it participates in the vascular supply of the posterior aspect of the elbow, forming anastomoses with other arteries around the joint.

Common Interosseous Artery

One of the major branches of the ulnar artery, the common interosseous artery arises early in the course of the ulnar artery. It divides into the anterior and posterior interosseous arteries, which supply the deep muscles of the forearm and also contribute to the blood supply of the interosseous membrane and the bones of the forearm.

• Anterior Interosseous Artery: Travels along the anterior surface of the interosseous membrane, supplying the deep flexor muscles of the forearm.
• Posterior Interosseous Artery: Passes through the interosseous membrane to reach the posterior aspect of the forearm, where it supplies the extensor muscles.

Palmar and Dorsal Carpal Branches

These small branches of the ulnar artery arise near the wrist. The palmar carpal branch contributes to the palmar carpal arch, which provides blood to the carpal bones and ligaments of the wrist. The dorsal carpal branch participates in the formation of the dorsal carpal arch, which supplies the dorsal aspect of the wrist and hand.

Termination

At the level of the wrist and hand, the ulnar artery passes through Guyon’s canal and enters the palm, where it plays a critical role in forming the superficial palmar arch. The ulnar artery curves across the palm, where it gives off several branches to supply the fingers.

• Superficial Palmar Arch: The ulnar artery primarily contributes to the formation of the superficial palmar arch. This arch is completed either entirely by the ulnar artery or with contributions from the superficial branch of the radial artery. The arch then gives rise to the common palmar digital arteries, which further divide into proper palmar digital arteries to supply the fingers.
• Deep Branch of the Ulnar Artery: In addition to its contribution to the superficial palmar arch, the ulnar artery also gives off a deep branch that contributes to the formation of the deep palmar arch, along with the radial artery. The deep palmar arch supplies the deeper structures of the hand.

Variations

The anatomy of the ulnar artery can vary between individuals. Some common variations include:

• High Origin of the Ulnar Artery: In some cases, the ulnar artery may originate higher in the arm than usual, arising from the brachial artery more proximally, even in the mid-arm.
• Incomplete Superficial Palmar Arch: In some individuals, the superficial palmar arch may not be fully formed, meaning that the ulnar artery may not complete its anastomosis with the superficial branch of the radial artery.

Relationship to Surrounding Structures

• Ulnar Nerve: The ulnar artery runs parallel to the ulnar nerve along the medial side of the forearm. At the wrist, both structures pass through Guyon’s canal before entering the hand.
• Muscles: The ulnar artery travels deep to the flexor carpi ulnaris in the forearm, while in the hand, it runs beneath the palmar aponeurosis and over the flexor tendons.
• Bones and Ligaments: The ulnar artery contributes to the vascular supply of the carpal bones via its carpal branches and provides blood to the bones of the forearm through its interosseous branches.

Function

The ulnar artery plays a critical role in supplying blood to the forearm, wrist, and hand. Its functions are essential for providing oxygenated blood to the muscles, bones, and skin of the upper limb, as well as ensuring proper vascularization of the hand. Below is a detailed breakdown of its specific functions.

Blood Supply to the Medial Forearm

The ulnar artery is the primary source of blood supply to the medial side of the forearm. It supplies both the superficial and deep muscles along this region:

• Flexor Carpi Ulnaris: The ulnar artery provides blood to the flexor carpi ulnaris muscle, which is responsible for flexing and adducting the wrist.
• Flexor Digitorum Superficialis and Profundus: The ulnar artery also supplies blood to the flexor digitorum superficialis and profundus muscles, which are involved in flexing the fingers and contributing to hand grip.
• Pronator Teres: The ulnar artery helps vascularize the pronator teres muscle, which aids in pronation (turning the palm downward).

This continuous blood flow is essential for muscle function and for providing energy to support the movements of the forearm and hand.

Blood Supply to the Elbow Joint

The ulnar artery contributes to the vascular network surrounding the elbow joint through its recurrent branches:

• Anterior Ulnar Recurrent Artery: This branch ascends toward the anterior part of the elbow, participating in an anastomotic network that helps supply the elbow joint and surrounding tissues.
• Posterior Ulnar Recurrent Artery: This branch supplies the posterior region of the elbow and also forms part of the anastomosis with the deep brachial and radial arteries.

These recurrent branches ensure that the elbow joint and surrounding muscles receive a constant blood supply, which is crucial for joint mobility and function, especially during activities that require flexion and extension of the arm.

Blood Supply to the Deep Structures of the Forearm

One of the important functions of the ulnar artery is to supply the deep structures of the forearm, primarily through its common interosseous artery and its subdivisions:

• Anterior Interosseous Artery: This branch supplies the deep flexor muscles, including the flexor digitorum profundus and flexor pollicis longus, as well as the interosseous membrane.
• Posterior Interosseous Artery: This branch supplies the extensor muscles of the forearm, which are responsible for extending the wrist and fingers.

The interosseous arteries play a critical role in maintaining the health and function of both the flexor and extensor muscle groups in the forearm, ensuring adequate blood flow during dynamic hand and wrist movements.

Blood Supply to the Wrist and Carpal Bones

The ulnar artery contributes to the blood supply of the wrist and carpal bones through its palmar and dorsal carpal branches:

• Palmar Carpal Branch: This small artery helps form the palmar carpal arch, which supplies the bones and ligaments of the wrist joint, particularly on the anterior aspect.
• Dorsal Carpal Branch: This branch forms the dorsal carpal arch, which supplies the bones and tendons on the back of the wrist.

These branches ensure that the wrist joint remains well-nourished, providing stability and flexibility during activities that involve wrist movement. The carpal bones rely on this arterial supply to maintain their structural integrity.

Formation of the Superficial Palmar Arch

One of the most important functions of the ulnar artery is its role in forming the superficial palmar arch, which is the primary source of blood to the palm and fingers.

• Common Palmar Digital Arteries: The ulnar artery gives rise to these arteries, which run along the palm and divide into proper palmar digital arteries.
• Proper Palmar Digital Arteries: These arteries supply blood to the fingers, running along the lateral and medial sides of each finger. They are critical for maintaining the health of the skin, muscles, and connective tissues of the fingers.

The superficial palmar arch ensures that the entire palm and fingers receive oxygenated blood, which is essential for hand function, sensation, and dexterity.

Contribution to the Deep Palmar Arch

In addition to forming the superficial palmar arch, the ulnar artery also contributes to the deep palmar arch via its deep branch. This contribution is essential for vascularizing the deep structures of the hand, including:

• Thenar and Hypothenar Muscles: These muscles, which control thumb and small finger movements, receive part of their blood supply from the deep palmar arch.
• Lumbrical and Interosseous Muscles: These small muscles, important for finger movements, also receive blood through the deep palmar arch.

By contributing to both the superficial and deep palmar arches, the ulnar artery ensures that the hand has a robust and comprehensive blood supply, even during gripping or fine motor tasks.

Collateral Circulation and Anastomosis

The ulnar artery is a key player in the hand’s collateral circulation, ensuring that blood can continue to flow even if other arteries are compromised.

Anastomosis with Radial Artery: The superficial and deep palmar arches, formed by the ulnar artery and radial artery, provide multiple routes for blood to reach the hand. This anastomotic network allows the hand to maintain an adequate blood supply, even in cases where one of the arteries is damaged or blocked.

This collateral circulation is crucial for protecting against ischemic events and ensuring that the hand remains functional in case of arterial injury or disease.

Oxygen and Nutrient Delivery

Like all arteries, the primary role of the ulnar artery is to deliver oxygen and nutrients to the tissues it supplies. The continuous flow of blood from the ulnar artery ensures that the muscles, skin, bones, and nerves in the forearm and hand receive the necessary oxygen and nutrients to maintain health and perform essential functions.

• Tissue Repair and Healing: The ulnar artery plays a critical role in providing oxygen and nutrients for tissue repair in the forearm and hand, particularly after injury or strain.
• Skin and Subcutaneous Tissue: The small branches of the ulnar artery also supply the skin and subcutaneous tissues of the hand, ensuring that the skin remains healthy and able to protect underlying structures.

Clinical Significance

The ulnar artery is clinically significant due to its vital role in supplying blood to the forearm, wrist, and hand. It is frequently involved in both diagnostic and therapeutic procedures.

• Trauma and Injury: The ulnar artery is vulnerable to injury in cases of trauma to the forearm or hand, particularly in the area around Guyon’s canal, where it becomes more superficial. Laceration or damage to the ulnar artery can lead to significant blood loss and compromise blood flow to the hand, requiring prompt surgical repair to prevent ischemia.
• Ulnar Artery Occlusion: In conditions like ulnar artery thrombosis or Raynaud’s disease, the blood flow through the ulnar artery may be impaired, leading to symptoms such as cold, pale, or cyanotic fingers. In severe cases, reduced blood supply can result in tissue ischemia and ulceration.
• Surgical and Diagnostic Procedures: The ulnar artery is often used in vascular assessments such as the Allen’s test, which evaluates the integrity of the arterial blood supply to the hand before radial artery catheterization or surgery. The ulnar artery’s role in forming the superficial palmar arch makes it essential in ensuring collateral circulation in case of radial artery compromise.