What Is Arterial Thoracic Outlet Syndrome? A Plain-Language Guide to the Arm Blood Flow Problem That Rarely Gets Spotted Early

Medically reviewed by Dr. Baraa Alnahhal, MD. Last reviewed October 13, 2026. This content is for educational purposes and is not medical advice.

Figure 1. ATOS happens when the subclavian artery gets squeezed between the collarbone and first rib, most often by an extra “cervical rib,” blocking blood flow and setting the stage for clots.

Quick Answer

Arterial thoracic outlet syndrome is a disorder in which the subclavian artery is compressed between the ribs and collarbone, blocking blood flow and allowing clots to form. [1] It causes arm ache or numbness that worsens with use [1] [2], and is most often due to an extra cervical rib. [1] [6] It is the least common type and almost always treated with surgery. [1] [2]

What the research says

• ATOS is rare, and surgery for it carries a higher complication risk than surgery for the nerve type. In a national U.S. inpatient database of 3,547 thoracic outlet syndrome operations from 2010 to 2015 (an estimated 18,210 nationally), 89.2% were neurogenic, 9.9% venous, and 0.9% arterial. Arterial cases had about four times the odds of a major complication compared with neurogenic cases (adjusted odds ratio 4.26; 95% CI 1.78 to 10.17), while overall mortality was 0.6% (George et al., Annals of Vascular Surgery, 2021) [5].

• Decompression surgery, with artery repair when needed, gave excellent results in one hospital’s series. Among 13 patients with ATOS treated over 11 years (mean age 43; 85% women), the most common presentation was arm claudication (54%), and cervical ribs showed up on X-ray in most cases. All 13 had surgical decompression, and 5 (38%) needed arterial reconstruction. At a mean follow-up of about 32.6 months, every artery or graft was open, vascular symptoms had completely resolved, and there were no deaths or amputations (Dalio et al., Annals of Vascular Surgery, 2021) [6].

• Cervical ribs that cause symptoms are often fused to the first rib, so both may need to be removed. In a Johns Hopkins review of 23 cervical rib resections in 20 patients, 7 presented with subclavian artery thrombosis (3 of them with subclavian artery aneurysms). Cervical ribs were fused to the first rib in 17 of 23 cases (74%), and the authors concluded that both the cervical rib and the first rib must be removed to relieve arterial compression (Chang et al., Journal of Vascular Surgery, 2013) [7].

What Is Arterial Thoracic Outlet Syndrome?

Arterial thoracic outlet syndrome (ATOS) is a disorder that affects the artery between your ribs and collarbone (clavicle). [1] This space between your ribs and collarbone is the thoracic outlet. [1]

Your arteries carry blood from your heart to the rest of your body. People with ATOS have a squeezed (compressed) artery in their thoracic outlet. The subclavian artery is compressed between the clavicle bone and first rib. [1] This compression blocks blood flow and allows blood clots to form. [1]

What Does Arterial Thoracic Outlet Syndrome Feel Like?

Arterial thoracic outlet syndrome causes symptoms that affect your fingers, hands, or entire arm. The most common sign is a dull ache or numbness in one arm. [1] [2] Symptoms are worse when you use your arm and better when you rest. [1] Usually, people with ATOS don’t have any symptoms in their neck or shoulder. [1]

ATOS can decrease your blood circulation. As a result, your fingers, hand, or arm may have:

Symptom sign	What it looks like
Dull ache or numbness	The most common sign, in one arm; worse with use, better with rest [1] [2]
Coldness	The fingers, hand, or arm feels cold [1] [4]
Numbness or tingling	A “pins and needles” feeling [1] [4]
Pain	Discomfort in the affected arm [1] [4]
Pale discoloration	The skin looks pale [1]
Slow-healing wounds	Cuts and wounds on the hand or arm take longer to heal [1]

What Causes Arterial Thoracic Outlet Syndrome?

Many people with ATOS were born with an extra rib above their collarbone. [1] This rib, called the cervical rib, sits above what is most people’s first rib. The extra cervical rib can compress the subclavian artery, blocking blood flow and allowing blood clots to form. [1] These blood clots may break off and travel through your arm, getting in the way of proper blood flow. [1] [4]

Other causes include:

Cause	How it contributes
Extra (cervical) rib	Born with a rib above the collarbone, or a rib in the wrong place, that compresses the artery [1] [4]
Obesity [1]	Puts extra pressure on your joints
Physical trauma	Such as an injury from a car accident [1]
Poor posture [1] [3]	Contributes to compression of the thoracic outlet
Pregnancy [1] [3]	Can contribute to compression
Repetitive movements	Swinging a tennis racket, throwing a softball or baseball, or lifting boxes overhead [1]

Figure 2. An extra “cervical rib” above the collarbone is the most common cause, pressing the subclavian artery closed. Obesity, trauma, poor posture, pregnancy, and repetitive overhead motion can also trigger it.

How Rare Is Arterial Thoracic Outlet Syndrome, and Who Gets It?

All types of thoracic outlet syndrome (TOS) are rare, and experts don’t know exactly how many people have it. Arterial TOS is the least common type of TOS [1] [2]: fewer than 1 in 100 cases of thoracic outlet syndrome are arterial thoracic outlet syndrome. [1] [4]

All types of thoracic outlet syndrome are more common in women ages 20 to 50. [1] [3] Usually, compression of the artery in the thoracic outlet happens because a person was born with an extra rib (a cervical rib), or a rib in the wrong place. [1] [4]

How Dangerous Is Arterial Thoracic Outlet Syndrome?

Arterial thoracic outlet syndrome is the most dangerous type of thoracic outlet syndrome. [1] Without treatment, ATOS can cause severe blood clots in your arteries, and the clots can affect blood flow to your arm and hand. [1] Rarely, the blood clots can also travel to your brain and cause strokes. [1]

If you don’t get treatment, ATOS can cause serious health problems. In some people, the wall of the artery expands and weakens, forming an aneurysm. [1] In severe cases, clots can move to your lungs, causing a pulmonary embolism. [1] Without treatment, ATOS can also cause wounds on your hand or, in extreme cases, loss of fingers. [1]

Complication	What it means
Severe blood clots	Clots in the arteries that affect blood flow to the arm and hand [1]
Clots in the lungs	In more severe cases, clots move to the lungs, causing a pulmonary embolism [1]
Stroke	Rarely, clots travel to the brain [1]
Aneurysm	The artery wall expands and weakens [1]
Hand wounds; loss of fingers	Severe complications without treatment [1]

How Is Arterial Thoracic Outlet Syndrome Diagnosed?

If you have signs of arterial thoracic outlet syndrome, your healthcare provider will visually examine your neck and shoulder area. You may perform specific movements so they can check your range of motion. [1] Your provider will also take your blood pressure and ask about your symptoms. [1] If they suspect ATOS, you may have more tests to evaluate your thoracic outlet.

Arterial thoracic outlet diagnosis may involve imaging tests. To view your arteries, blood flow, and internal structures, you may have:

Test	How it works
Ultrasound	Uses sound waves to look inside your body, including blood flow. Most often the first test used to look for this diagnosis. [1]
Arteriogram [1] [4]	A small, hollow tube (catheter) and contrast dye are placed in your arteries, then an X-ray is taken.
CT scan [1]	Uses multiple X-rays to create detailed images.
MRI [1]	Uses radio waves and magnets to get a detailed picture.
X-ray [1]	Uses targeted, safe doses of radiation to get images.

Figure 3. Diagnosis starts with an exam of the neck and shoulder plus an ultrasound, then CT, MRI, X-ray, or an arteriogram if needed. Treatment almost always means surgery to remove the extra rib or rebuild the artery.

How Is Arterial Thoracic Outlet Syndrome Treated?

Arterial thoracic outlet syndrome treatment almost always involves surgery. [1] [4] Before the operation, your healthcare provider may give you medication such as warfarin (Coumadin) or heparin (Hep-Lock) to break up blood clots. [1] They may also try to remove clots that are already there, either by injecting medication or by performing a procedure. [1]

During arterial thoracic outlet syndrome surgery, your healthcare provider may:

Surgery option	What it does
Remove part of the extra rib [1] [4]	Relieves pressure on the artery
Arterial graft [1] [4]	Replaces a damaged artery with part of a healthy artery from another part of your body
Artificial tube [1]	Replaces a damaged artery with an artificial tube to redirect blood flow

What Is the Outlook?

Without treatment, arterial thoracic outlet syndrome can cause severe complications such as blood clots, wounds on your hand, or (in extreme cases) loss of fingers. Thankfully, early treatment increases your chances of a successful outcome. [1] If you have any symptoms that could point to ATOS, see your healthcare provider right away.

How Can I Lower My Risk?

There’s no guaranteed way to prevent ATOS. But you can lower your risk of compression injuries with a few lifestyle changes [1]:

Prevention step	What to do
Maintain a healthy weight	Achieve and maintain a healthy weight [1] for your body type, age, and sex
Watch your bags	Avoid carrying heavy bags on one shoulder [1]
Limit overhead work	Limit repetitive overhead movements [1]
Strengthen shoulders [1]	Weight lifting or resistance exercises
Stretch daily	Stretch your neck, shoulders, and chest every day [1]

What is the bottom line on arterial thoracic outlet syndrome?

Arterial thoracic outlet syndrome is the rarest and most dangerous type of thoracic outlet syndrome, and its story always starts in the same narrow space: the gap between the collarbone and first rib where the subclavian artery carries blood to the arm, hand, neck, and head. Most often the squeeze comes from an extra rib a person was born with, though obesity, trauma, poor posture, pregnancy, and repetitive overhead movement can also close the gap.

The squeeze blocks blood flow and lets clots form, and those clots can travel through the arm, or in severe cases to the lungs, brain, or cause an aneurysm in the artery wall. Symptoms stay in the arm, not the neck or shoulder: a dull ache or numbness in one arm that worsens with use, plus coldness, tingling, pain, paleness, or slow-healing wounds.

Because treatment almost always involves surgery (removing part of the extra rib, grafting in healthy artery, or redirecting flow through an artificial tube), early diagnosis with ultrasound and other imaging matters enormously. Untreated ATOS can end in severe clots, hand wounds, and even loss of fingers, but early treatment greatly improves the odds of a full recovery. If you have any symptoms that could point to ATOS, see your healthcare provider right away.

Take the Next Step

If one arm aches or goes numb when you use it, especially with coldness, tingling, pain, paleness, or wounds that heal slowly, don’t write it off as a pinched nerve, particularly if you have a known extra rib or do repetitive overhead work like throwing or lifting boxes. Ask your healthcare provider for an exam of your neck and shoulder, and expect an ultrasound as the first look at your blood flow.

See your provider right away rather than waiting, because untreated ATOS can cause severe blood clots, hand wounds, and in extreme cases loss of fingers. Early treatment, which almost always involves surgery plus clot-busting medication such as warfarin or heparin, increases your chances of a successful outcome. If you’re diagnosed, ask which surgery fits your case (rib removal, artery graft, or artificial tube), what lifestyle changes will protect your recovery, and how to lower your risk with weight management, shoulder strengthening, daily stretching, and lighter, evenly balanced loads.

Frequently Asked Questions

What is arterial thoracic outlet syndrome? A disorder of the artery between your ribs and collarbone, the space called the thoracic outlet, in which the subclavian artery is compressed between the clavicle and first rib, blocking blood flow and allowing blood clots to form.

What does it feel like? The most common sign is a dull ache or numbness in one arm. Symptoms are worse when you use your arm and better when you rest. Your fingers, hand, or arm may also feel cold, tingle, ache, look pale, or heal wounds slowly. Usually there are no symptoms in the neck or shoulder.

What causes it? Many people with ATOS were born with an extra rib above the collarbone, called a cervical rib, which compresses the subclavian artery. Other causes include obesity, physical trauma such as a car accident injury, poor posture, pregnancy, and repetitive movements like swinging a tennis racket, throwing a ball, or lifting boxes overhead.

How rare is it? All types of thoracic outlet syndrome are rare, and arterial TOS is the least common type: fewer than 1 in 100 cases of thoracic outlet syndrome are arterial. All types are more common in women ages 20 to 50.

Can the blood clots be dangerous? Yes. The clots can affect blood flow to the arm and hand, and in more severe cases can move to the lungs and cause a pulmonary embolism. Rarely, clots can travel to the brain and cause strokes.

What complications happen without treatment? Without treatment, ATOS can cause severe blood clots, wounds on your hand, and in extreme cases loss of fingers. The artery wall can also expand and weaken, forming an aneurysm.

How is it diagnosed? A provider examines your neck and shoulder visually, has you perform movements to check range of motion, takes your blood pressure, and asks about symptoms. Imaging tests may include ultrasound (usually the first test), arteriogram, CT scan, MRI, or X-ray.

How is it treated? Treatment almost always involves surgery. Before the operation, medication such as warfarin (Coumadin) or heparin (Hep-Lock) may break up blood clots, and existing clots may be removed by injection or procedure. Surgery can remove part of the extra rib, replace the damaged artery with a healthy artery graft, or replace it with an artificial tube.

Will nonsurgical treatments help? Because treatment almost always involves surgery, nonsurgical options are limited. Discuss with your provider whether any nonsurgical treatments could improve your symptoms.

What is the outlook? Early treatment increases your chances of a successful outcome. If you have any symptoms that could point to ATOS, see your healthcare provider right away.

How can I lower my risk? There’s no guaranteed way to prevent ATOS, but you can lower your risk of compression injuries by maintaining a healthy weight, avoiding heavy bags on one shoulder, limiting repetitive overhead movements, strengthening your shoulders, and stretching your neck, shoulders, and chest daily.

What questions should I ask my doctor? Ask about the most likely cause of your symptoms, which tests you need for diagnosis, what treatment options exist, whether nonsurgical treatments will improve your symptoms, and what lifestyle changes can help.

Related Reading

• Thoracic Outlet Syndrome (Cleveland Clinic): The broader family of conditions (nerve, vein, and artery) that share the same compressed outlet space.

• Cervical Rib (Cleveland Clinic): The extra rib above the collarbone that causes most arterial TOS cases.

• Blood Clots (Cleveland Clinic): What happens when clots form, travel, and block blood flow.

Learn more in our guide to Pulse Volume Recording (PVR Test): What It Is, How It's Done and Results.

References

1. Cleveland Clinic. Arterial Thoracic Outlet Syndrome. Cleveland Clinic. Last updated April 29, 2022. https://my.clevelandclinic.org/health/diseases/23004-arterial-thoracic-outlet-syndrome

2. Daniels B, et al. Arterial thoracic outlet syndrome. Curr Sports Med Rep. 2014;13(2):75-80. PMID 24614419. https://doi.org/10.1249/JSR.0000000000000034

3. National Library of Medicine. Thoracic Outlet Syndrome. MedlinePlus. Last updated December 3, 2025. https://medlineplus.gov/thoracicoutletsyndrome.html

4. Sanders RJ. Thoracic Outlet Syndrome. National Organization for Rare Disorders. Last updated May 15, 2015. https://rarediseases.org/rare-diseases/thoracic-outlet-syndrome/

5. George EL, et al. Contemporary Practices and Complications of Surgery for Thoracic Outlet Syndrome in the United States. Ann Vasc Surg. 2021;72:147-158. PMID 33340669. https://doi.org/10.1016/j.avsg.2020.10.046

6. Dalio MB, et al. Contemporary Management of Arterial Thoracic Outlet Syndrome. Ann Vasc Surg. 2021;74:42-52. PMID 33556514. https://doi.org/10.1016/j.avsg.2021.01.078

7. Chang KZ, et al. The significance of cervical ribs in thoracic outlet syndrome. J Vasc Surg. 2013;57(3):771-5. PMID 23446121. https://doi.org/10.1016/j.jvs.2012.08.110

Medical disclaimer

This guide is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment. If you have a one-sided arm ache with numbness, coldness, paleness, or slow-healing wounds, especially with a known extra rib, see a healthcare provider promptly. Always seek the advice of a physician or other qualified health provider with any questions about a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read here.