Ulnar Collateral Arteries

The ulnar collateral arteries are two important branches of the brachial artery that contribute to the rich anastomotic network around the elbow joint. These include the superior ulnar collateral artery and the inferior ulnar collateral artery. Together, they provide critical collateral circulation in the event of brachial artery occlusion or compression during elbow flexion, and they help perfuse the elbow joint, distal arm, and proximal forearm.

Classification

Superior Ulnar Collateral Artery

Origin

Arises from the brachial artery approximately midway down the arm, just distal to the origin of the deep brachial (profunda brachii) artery.

Course

• Descends medially with the ulnar nerve.
• Passes posterior to the medial epicondyle of the humerus.
• Pierces the medial intermuscular septum to reach the posterior compartment.
• Runs deep to the triceps brachii and medial head of the brachialis.

Termination

Anastomoses with the posterior ulnar recurrent artery (a branch of the ulnar artery) posterior to the medial epicondyle, contributing to the posterior elbow anastomosis.

Inferior Ulnar Collateral Artery

Origin

Arises from the brachial artery superior to the elbow joint, usually around 5 cm above the medial epicondyle.

Course

• Runs medially across the brachialis muscle.
• Passes anterior to the medial epicondyle of the humerus.
• Travels superficial to the joint capsule but deep to the skin and fascia.

Termination

Anastomoses with the anterior ulnar recurrent artery (from the ulnar artery) anterior to the medial epicondyle.

Function

• Collateral circulation: Maintain arterial perfusion to the forearm and hand when the elbow is flexed and the brachial artery may be compressed.
• Joint supply: Both arteries contribute to the periarticular arterial anastomosis of the elbow joint, which supplies the capsule, ligaments, and surrounding tissues.

Physiological Role(s)

• Enable continuous blood flow to the forearm regardless of joint positioning.
• Assist in thermoregulation of the elbow area by modulating cutaneous blood flow.
• Support tissue healing and inflammatory response during elbow trauma or overuse syndromes.

Relations

Superior Ulnar Collateral

• Medial to the brachial artery in its upper course.
• Travels closely with the ulnar nerve, especially posterior to the medial epicondyle.
• Deep to the triceps brachii and intermuscular septum.

Inferior Ulnar Collateral

• Anterior to the humerus and brachialis muscle.
• Crosses the elbow anterior to the medial epicondyle.
• Superficial to the joint capsule but deep to fascia.

Development

These arteries form during vascular remodeling of the upper limb bud in embryogenesis. They arise from the axial artery system, which forms the basis of the brachial artery. Collateral pathways including the ulnar collateral arteries are essential adaptations that appear early to accommodate mobility and growth of the joint. Their development coincides with the branching of the radial and ulnar arteries and maturation of periarticular vascular arcs.

Clinical Significance

• Collateral flow preservation: In brachial artery ligation or injury (e.g., trauma, tumor resection, catheter injury), the ulnar collateral arteries are vital in preserving limb perfusion.
• Elbow trauma: Fractures or dislocations around the medial epicondyle may damage these vessels, particularly the superior ulnar collateral artery due to its proximity to the ulnar nerve.
• Iatrogenic injury: Surgeries involving the medial aspect of the elbow (e.g., cubital tunnel release) require caution to preserve these arteries.
• Arterial embolism or occlusion: If embolic blockage of the brachial artery occurs proximally, these collateral vessels may maintain minimal perfusion to the distal limb until revascularization is established.

Imaging

• CT Angiography: Best modality for visualizing the elbow’s arterial anastomosis and collateral vessels.
• Doppler Ultrasound: Can demonstrate blood flow continuity across the elbow during flexion and extension.
• MRI: Useful in evaluating vascular injuries associated with soft tissue trauma around the elbow.

Anatomical Variations

• May arise at variable distances from the brachial artery, with proximal or distal shifts reported.
• May share a common trunk with other branches (e.g., deep brachial or nutrient artery).
• In rare cases, either artery may be hypoplastic or duplicated.
• Accessory communicating branches may link the ulnar collateral arteries directly or anastomose with neighboring muscular branches.

Collateral Anastomoses of the Elbow (Summary)