The ulnar artery is one of the two main arteries supplying blood to the forearm and hand, running along the inner (pinky) side of the forearm from the elbow to the palm. It is typically the larger of the two forearm arteries and serves as the dominant blood supply to the hand in most people, feeding the superficial palmar arch that delivers blood to the fingers. Despite receiving less public attention than the radial artery on the thumb side, the ulnar artery sits at the center of a surprising range of clinical situations, from cardiac procedures and reconstructive surgery to occupational injuries and autoimmune disease.
Course Through the Forearm and Hand
The ulnar artery branches off the brachial artery just below the elbow crease, in the area called the cubital fossa. From there it dives deep beneath the forearm flexor muscles, traveling alongside the ulnar nerve for most of its path toward the wrist. In the upper forearm, it gives off the common interosseous artery, a branch that splits further to supply the deep structures between the radius and ulna bones. As it approaches the wrist, the ulnar artery becomes more superficial, passing through a narrow channel on the pinky side of the wrist called Guyon’s canal. This canal is formed by two small wrist bones and a ligament stretched between them. After exiting Guyon’s canal, the artery fans out into the superficial palmar arch, a curved vessel that loops across the palm and sends branches to each finger.
The relationship between the ulnar artery and the ulnar nerve is clinically important. The two structures travel together through much of the forearm and share Guyon’s canal at the wrist. Variations in the anatomy of Guyon’s canal, including differences in the artery’s branching pattern and course, can contribute to nerve compression or change how surgeons approach the area.
How the Hand’s Backup Blood Supply Works
The hand has built-in redundancy. Two arterial arches, one superficial and one deep, connect the ulnar and radial arteries so that if one is blocked or cut, the other can still feed the fingers. In practice, though, this backup system is less reliable than textbooks sometimes suggest. A cadaver study of 50 hands found that a textbook-perfect superficial palmar arch, where the ulnar and radial arteries form a complete loop, was present in only about 10% of hands. The ulnar artery’s superficial branch supplied blood to all five fingers in roughly two-thirds of hands, while a direct connection between the radial and ulnar arteries in the superficial arch existed in only about a third.1PubMed. Surgical implications of variations in hand collateral circulation: anatomy revisited The reassuring finding was that every hand had at least one major vessel linking the two arteries, even when the classic arch pattern was absent.
A separate anatomical study confirmed that the ulnar artery dominates the superficial palmar arch in most people. About two-thirds of hands showed an ulnar-type arch, with the majority of those formed entirely by the ulnar artery alone, without meaningful contribution from the radial side.2PubMed Central. Variation in formation of superficial palmar arches with clinical implications This ulnar dominance explains why damage to the ulnar artery at the wrist can have outsized consequences for finger blood flow, and why surgeons test hand circulation carefully before harvesting either forearm artery for other uses.
Testing Hand Circulation Before a Procedure
Before any procedure that might compromise the ulnar or radial artery, whether it is a catheter insertion, arterial blood draw, or surgery to harvest a vessel, clinicians want to know whether the remaining artery can keep the hand alive on its own. The standard bedside check is the modified Allen test. You make a tight fist while someone compresses both arteries at your wrist. When you open your hand, it looks pale. The examiner then releases one artery and watches how quickly color returns. A slow return suggests the other artery may not be providing adequate backup.
The test is quick and requires no equipment, but its accuracy has been debated. A study comparing the modified Allen test against Doppler ultrasound measurements of thumb blood flow found that a delayed recovery time on the Allen test does predict reduced flow in the thumb’s digital artery, supporting its use as a first-line screening tool.3PubMed. Preoperative assessment of hand circulation by means of Doppler ultrasonography and the modified Allen test In higher-stakes situations, such as planning a free-flap surgery, many surgeons follow up with Doppler ultrasound or CT angiography for a more detailed picture of the hand’s arterial anatomy. CT angiography in particular has become a highly accurate tool for mapping upper-limb arteries in patients with nontraumatic vascular problems.4American Journal of Roentgenology (AJR). CT angiography of the upper extremity arterial system: Part 2- Clinical applications beyond trauma patients
Anatomical Variations and the Superficial Ulnar Artery
Not everyone’s ulnar artery follows the standard deep course beneath the forearm muscles. A variant called the superficial ulnar artery runs above the muscles instead of beneath them, traveling just under the skin and the thin sheet of tissue covering the forearm. Depending on the study, this variant shows up in roughly 1 to 7% of people.5PubMed Central. A rare variant of the superficial ulnar artery, and its clinical implications: a case report It can arise from the brachial artery, the axillary artery, or in rare cases even from the radial artery.6Folia Morphologica. Anatomical variations of the superficial ulnar artery: case series observed on historical specimens prepared by Ludwik Karol Teichmann
This matters practically because a superficial ulnar artery can be mistaken for a vein. It sits in a position where someone drawing blood or inserting an IV line might accidentally puncture it, leading to unexpected bleeding, hematoma, or accidental injection of medication into an artery instead of a vein. Awareness of this variant is particularly important for emergency room staff and anesthesiologists.
How the Ulnar Artery Develops Before Birth
The arterial pattern of the arm does not form as a single predetermined blueprint. A study of 112 human embryos (224 upper limbs) showed that the process unfolds in two stages. First, a mesh of tiny capillaries sprouts from the aorta during early embryonic development. Then, selected capillaries enlarge and mature into recognizable arteries in a wave that sweeps from the shoulder toward the fingertips. The subclavian and axillary arteries take shape around the fifth week, the brachial artery extends to the elbow by the sixth, and the forearm arteries including the ulnar reach their adult form by about the eighth week.7PubMed Central. Development of the arterial pattern in the upper limb of staged human embryos: normal development and anatomic variations Hiccups in this remodeling process explain the variations seen in adults, including the superficial ulnar artery described above.
Hypothenar Hammer Syndrome
Just after passing through Guyon’s canal, the ulnar artery crosses a roughly two-centimeter stretch where it is covered by nothing more than a thin muscle and a bit of fat. Beneath it sits the hook of the hamate, one of the small carpal bones. This arrangement makes the artery vulnerable to repetitive blunt force against the heel of the palm, a mechanism that gives hypothenar hammer syndrome its name.
People who use the heel of their hand as a striking tool, whether from manual labor, martial arts, or habitual palm-banging on hard surfaces, can damage the inner lining of the artery. The result is a cascade that can include vessel spasm, blood clot formation, and in some cases a small aneurysm that forms when the artery wall weakens. Clots from the damaged segment can break free and travel downstream, blocking the tiny digital arteries and causing pale, painful, or numb fingers.8Journal of Orthopedic Research and Therapy. Hypothenar Hammer Syndrome Due to Penetrating Trauma: Case Report & Brief Review The condition can also follow a single penetrating injury to the same area. Diagnosis usually involves Doppler ultrasound or angiography, and treatment ranges from medication to dissolve clots to surgical reconstruction of the damaged arterial segment.
Cardiac Catheterization Through the Ulnar Artery
When cardiologists thread a catheter into the heart to perform an angiogram or open a blocked coronary artery, they need an entry point. For decades the femoral artery in the groin was the default, but the radial artery at the wrist has largely replaced it because patients can walk sooner and bleeding complications are fewer. The ulnar artery has been explored as yet another option, particularly when the radial artery is too small, has already been used, or has been harvested for bypass surgery.
Early feasibility work showed the ulnar approach could work. In one of the first dedicated reports, successful puncture was achieved in 93% of attempts, and all procedures could be completed through the ulnar route without switching to another site.9PubMed Central. Safety and feasibility of transulnar cardiac catheterization But a larger randomized trial comparing the two wrist arteries head to head found that using the ulnar artery as the first-choice strategy led to higher crossover rates, meaning operators had to switch to a different artery more often because of access difficulties. That trial concluded the ulnar route should not be considered an acceptable first-line alternative to the radial approach.10PubMed. Transulnar compared with transradial artery approach as a default strategy for coronary procedures: a randomized trial. The Transulnar or Transradial Instead of Coronary Transfemoral Angiographies Study (the AURA of ARTEMIS Study)
A meta-analysis of randomized trials largely agreed, finding similar safety and effectiveness between the two approaches except for a higher initial puncture failure rate and more frequent need to switch access sites with the ulnar route.11PubMed. Transulnar versus transradial access for coronary angiography or percutaneous coronary intervention: A meta-analysis of randomized controlled trials An interesting twist appeared in complication data from a separate trial: arterial occlusion after the procedure was significantly more common after radial access (about 9%) than ulnar access (about 1%), and arterial spasm during the procedure was also much higher on the radial side.12PubMed Central. Transulnar versus transradial approach for coronary angiography and angioplasty: Considering their complications Another randomized comparison of procedural success found no significant difference in complication rates between the two approaches when the procedure was completed through the assigned artery.13PubMed Central. Transulnar versus Transradial Access as a Default Strategy for Percutaneous Coronary Intervention
The practical upshot is that the ulnar artery is a reasonable backup when the radial artery is not available, but its smaller size and slightly trickier puncture keep it from replacing the radial artery as the go-to wrist access site for cardiac procedures.
Ulnar Artery Occlusion in Systemic Sclerosis
Systemic sclerosis, an autoimmune condition that causes hardening and thickening of the skin and connective tissue, can wreak havoc on blood vessels. The ulnar artery turns out to be a frequent casualty. A multicenter study of more than 200 patients found ulnar artery occlusion in about 37% of cases, with bilateral involvement in about two-thirds of those affected. Occlusion was strongly linked to a history of fingertip ulcers, more extensive skin thickening, and reduced lung function.14PubMed. Ulnar Artery Occlusion and Severity Markers of Vasculopathy in Systemic Sclerosis: A Multicenter Cross-Sectional Study
A smaller cohort study using Doppler ultrasound reported ulnar artery occlusion in about 28% of systemic sclerosis patients, with bilateral occlusion in three-quarters of those cases. Notably, over 80% of patients with occluded ulnar arteries also had digital ulcers, and the highest rates of occlusion appeared in patients with the most advanced patterns of tiny-vessel damage visible under capillaroscopy.15PubMed Central. Peripheral Macrovascular Involvement in Systemic Sclerosis: A Cohort Study by Color and Spectral Doppler Ultrasonography Earlier work looking specifically at patients with severe Raynaud’s phenomenon and digital ulceration had already documented the connection between ulnar artery disease and scleroderma, using angiography to confirm occlusions in patients who showed abnormal Allen tests.16PubMed. Ulnar artery involvement in systemic sclerosis (scleroderma)
For people living with systemic sclerosis, this research has shifted clinical attention. Doctors now often assess the ulnar artery directly rather than focusing only on the tiny capillaries in the fingernails, because ulnar artery occlusion appears to be a marker of more widespread and more severe vascular disease throughout the body.
The Ulnar Artery in Reconstructive and Bypass Surgery
Surgeons sometimes harvest tissue from the forearm, including skin, underlying fat, and a feeding artery, to reconstruct defects elsewhere in the body. The radial forearm free flap has been the workhorse for decades, particularly for head and neck reconstruction after cancer surgery. The ulnar forearm free flap, built around the ulnar artery, serves as an alternative with a few potential cosmetic advantages: the donor-site scar ends up on the inner aspect of the forearm where it is less visible, and the skin paddle can be thinner. A series of 15 ulnar forearm flaps used for head and neck reconstruction showed all flaps survived, with only minor wound-healing issues at the donor site and no abnormal sensation from ulnar nerve damage.17PubMed. The ulnar forearm free flap for the reconstruction of soft tissue defects in the head and neck area: free flap outcome and donor site outcome
A newer refinement, the ulnar artery perforator flap, harvests skin and fat nourished by small branches of the ulnar artery without sacrificing the main trunk. A prospective comparison of 98 patients who received either a radial forearm flap or an ulnar artery perforator flap found no significant differences in grip strength, sensation, temperature sensitivity, or cold intolerance at one year. Both groups returned to baseline function.18PubMed. Prospective Comparison of Donor-Site Morbidity following Radial Forearm and Ulnar Artery Perforator Flap Harvest The perforator-flap approach is appealing because it preserves the ulnar artery itself, maintaining the hand’s blood supply and keeping future surgical options open.
The ulnar artery has also been tried as a conduit in coronary artery bypass grafting. Because it is a muscular artery with similar properties to the radial artery, it was tested as a graft in a small series where eight of ten harvested ulnar arteries were successfully grafted onto coronary arteries. Two were rejected before grafting due to calcification or atherosclerosis found during preparation. No early complications in the hand or heart were noted in the patients who received grafts.19PubMed. Ulnar artery as a coronary bypass graft This use has remained niche, however, largely because the radial artery and internal thoracic artery provide more proven long-term results.
Traumatic Injury and Compartment Syndrome
Blunt or penetrating trauma to the forearm can tear the ulnar artery, and the consequences extend beyond blood loss. Because the forearm’s muscles and vessels are packed into tight compartments wrapped in tough connective tissue, bleeding from a ruptured ulnar artery can build up pressure within these compartments faster than the tissues can tolerate. A documented case involved a traumatic rupture of the ulnar artery with no accompanying bone fracture. The resulting hematoma raised compartment pressures enough to produce acute compartment syndrome, a surgical emergency requiring fasciotomy to prevent permanent muscle and nerve damage.20PubMed Central. Compartment syndrome resulting from undetected ulnar artery injury in the absence of a forearm fracture
The clinical lesson is that forearm compartment syndrome does not require a fracture. When someone has significant forearm swelling after a blow or laceration, clinicians need to consider arterial injury even if X-rays come back clean. The ulnar artery’s position deep in the forearm means that bleeding can accumulate silently for hours before the classic signs of compartment syndrome, severe pain, tightness, and pain on passive finger extension, become unmistakable.
Treating Finger Ischemia Through the Ulnar Artery
When blood flow to the fingers is suddenly cut off, whether from a clot, an embolus from a damaged upstream vessel, or vasospasm, the result can be painful, discolored, or numb fingers that are at risk of tissue death. Catheter-directed thrombolysis, where a thin catheter is threaded to the site of the clot and clot-dissolving medication is delivered directly, is one treatment option. A study of patients with acute finger ischemia found that about half of those treated with thrombolysis showed anatomic improvement on follow-up angiography, and patients who received the treatment before tissue loss had developed showed a trend toward better finger survival at 60 days.21Journal of Vascular Surgery. Anatomic findings and outcomes associated with upper extremity arteriography and selective thrombolysis for acute finger ischemia
The ulnar artery itself can serve as the access point for these interventions. A case report described successful thrombolysis for acute upper limb ischemia performed through an antegrade puncture of the proximal ulnar artery. A microcatheter was advanced into the superficial palmar arch, and a clot-dissolving drug was infused directly. Finger discoloration resolved and follow-up imaging confirmed improved digital artery flow.22International Journal of Angiology. Catheter-Directed Thrombolysis with Ulnar Artery Access in Acute Upper Limb Ischemia: A Rare Approach This approach is uncommon but illustrates how the ulnar artery’s direct line into the palmar arch can be exploited when conventional access routes are not feasible.
Comparative Anatomy Across Primates
The ulnar artery’s anatomy is not identical across primate species, and these differences offer a window into how limb blood supply has been rearranged over evolutionary time. In humans, the common interosseous artery typically branches off the ulnar artery shortly after its origin near the elbow. In the Japanese macaque, the branching pattern differs: the common interosseous artery arises from the ulnar artery rather than from the brachial artery, a configuration that sets the macaque apart from many other primates.23BioMed Research International. Comparative Gross Anatomy of the Forelimb Arteries of the Japanese Monkey (Macaca fuscata) and a Comparative Pattern of Forelimb Arterial Distribution in Primates These interspecies differences in forearm arterial branching are thought to reflect different functional demands on the hand and wrist across primate lineages, from species that walk on their knuckles to those that grip branches to those that use fine manual dexterity.