What Is Thoracic Outlet Syndrome, and Is Posture to Blame?
Thoracic outlet syndrome (TOS) happens when nerves or blood vessels are squeezed in the narrow space between your collarbone and your first rib. This causes numbness, tingling or pain in the arm and hand. Poor posture, especially rounded shoulders and a head that sits forward, can narrow that gap further. It is a common contributing factor.
Key takeaways
- TOS compresses the brachial plexus nerves or the subclavian vessels as they pass through the thoracic outlet.
- Symptoms include numbness in the arm, tingling in the fingers and weakness in the hand. They are often worse when the arm is raised.
- Rounded shoulders, forward head posture and tight muscles are common triggers.
- Standing whole-body imaging can show skeletal factors, such as a cervical rib or uneven shoulders, that lying-down scans may miss.
- Vascular TOS (involving blood vessels) can be serious. If you notice sudden swelling in the arm, a change in colour or coldness, get urgent medical help.
The thoracic outlet is a small triangle of space just behind your collarbone. The brachial plexus, a bundle of nerves that controls feeling and movement in the arm, passes through it. The subclavian artery and vein pass through it too. When that space gets too tight, the nerves or vessels are compressed. The result is thoracic outlet syndrome.
Most people with TOS have the neurogenic form, which means the nerves are affected. It is far more common than the vascular type. Its symptoms can overlap with cervical radiculopathy, where a pinched nerve in the neck causes similar tingling in the arm. Getting the right diagnosis matters, because each condition is managed in quite a different way.
What are the symptoms of thoracic outlet syndrome?
The most common symptoms of thoracic outlet syndrome are numbness, tingling and aching pain that travel from the shoulder down the arm into the hand. These feelings are often worst in the ring and little fingers. They tend to flare up when the arm is raised, for example when driving, typing overhead or drying your hair.
Red-flag warning. If your arm suddenly becomes swollen, turns pale or blue, or feels cold, these may be signs of vascular TOS, which needs urgent medical attention. Contact your doctor, call your local emergency number, or go to the nearest emergency department straight away.
What causes thoracic outlet syndrome?
Thoracic outlet syndrome is caused by anything that narrows the space between the collarbone and the first rib. This can be a structural issue you were born with, a habit that slowly tightens the area, or both together.
A cervical rib is a well-known structural cause. It is a small extra rib that sits above the normal first rib and takes up space in an already tight corridor. Not everyone with a cervical rib gets symptoms. But when posture problems or muscle tension are added on top, it can tip the balance.
What are the different types of thoracic outlet syndrome?
There are three recognised types. Neurogenic TOS accounts for the vast majority of cases. The arterial and venous forms are much rarer but more urgent.
Neurogenic TOS is the most common type. It happens when the brachial plexus nerves are compressed. Symptoms include numbness, tingling, pain and weakness in the arm and hand. It is often linked to posture, tight scalene muscles and repeated use of the arm.
Venous TOS involves compression of the subclavian vein. The arm may swell, feel heavy and look slightly blue. This type needs a prompt medical assessment. If you notice these signs, get urgent advice from your doctor, call your local emergency number, or go to the nearest emergency department.
Arterial TOS is the rarest and most serious type. The subclavian artery is compressed, which can lead to a pale, cold arm and a weakened pulse. This is a medical emergency. Go to the nearest emergency department if you suspect it.
How does posture contribute to thoracic outlet syndrome?
Posture is one of the most important factors in neurogenic TOS that can be changed. When your shoulders round forward and your head drifts ahead of your spine, the collarbone drops and the scalene muscles shorten. This reduces the space in the thoracic outlet and increases pressure on the nerves.
Think of the body as a connected chain. Forward head posture changes the curve of the upper spine. That tilts the shoulder blades, which shifts the collarbones inward. None of these happen on their own. That is why a scan of the shoulder alone may look normal, while a full standing view of the spine and shoulders together shows the postural pattern driving the compression.
Desk work, carrying heavy bags and even sleeping with your arms overhead can strengthen these patterns over months and years. The muscles around the neck and chest adapt to the new position. This makes the narrowing feel permanent, even though it is often reversible with the right guidance.
Wondering whether your posture is adding to your arm symptoms? A standing whole-body scan shows skeletal alignment from head to toe, the part that lying-down imaging cannot capture.
Book a free video consultationHow is thoracic outlet syndrome assessed with imaging?
TOS is usually diagnosed through a mix of clinical tests and imaging. Standard X-rays can spot a cervical rib. But they are taken lying down or of a single area, which relaxes the muscles and can hide the postural factors that narrow the outlet in real life.
ScanAlign standing EOS imaging captures your full skeleton while you are upright and bearing your own weight. This means the natural curves of your spine, the position of your collarbones and the alignment of your shoulders are all recorded as they really sit when gravity is acting on them. If you have uneven shoulders, a subtle curve in the spine or a pelvic tilt that carries upward, it will be visible on the image.
EOS imaging uses about 90% less radiation than a standard X-ray, around ten times less. The scan itself takes only seconds and there is no enclosed tunnel.
When is MRI the better choice? EOS shows bones, joints and alignment clearly. For soft tissue detail, such as the brachial plexus nerves, discs or blood vessels, MRI is usually the better tool. Your clinician may recommend both, depending on your symptoms. Nerve conduction studies are another option that can confirm whether the nerves are being compressed.
What helps manage thoracic outlet syndrome?
Treatment for TOS depends on which type you have and what is causing the compression. ScanAlign is a diagnostic imaging clinic, not a treatment provider, so the information below is general. Your treating clinician will advise on the right plan for you.
- Postural correction. Physiotherapy that focuses on opening the chest, strengthening the upper back and stretching the scalene muscles is a common first step for neurogenic TOS.
- Changes at work. Changing your desk height, your screen position or the way you carry bags can reduce the postural strain that narrows the outlet.
- Targeted exercises. Gentle exercises that draw the shoulder blades back and mobilise the upper spine are often recommended. Your physiotherapist will guide these.
- Understanding the cause. Knowing whether a cervical rib, a postural pattern or a muscle imbalance is the main driver helps your clinician focus treatment where it matters most. This is where detailed standing imaging can make a real difference.
If your symptoms overlap with those of a trapped nerve in the neck, your clinician may also want to rule out cervical radiculopathy treatment pathways before settling on a plan.
Is a standing posture scan right for you?
A standing EOS scan is not for everyone. Here is a quick guide.
Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.
- Long-standing numbness or tingling in the arm without a clear cause
- Symptoms that get worse when you raise your arm
- Rounded shoulders or a known postural imbalance
- Earlier imaging that did not give a clear answer
- A suspected cervical rib
- Sudden swelling, colour change or coldness in the arm
- Weakness or loss of function that is getting worse quickly
- Numbness together with loss of bladder or bowel control
Frequently asked questions about thoracic outlet syndrome
Raising the arm can narrow the thoracic outlet further and increase pressure on the brachial plexus nerves. This is one of the hallmark signs of neurogenic TOS. If it happens regularly, it is worth getting assessed.
Cervical radiculopathy pinches a nerve at the spine, usually affecting specific dermatomes. TOS compresses the nerve bundle lower down, near the collarbone. The symptoms can overlap, which is why an accurate diagnosis matters.
Yes. Rounded shoulders and a head that sits forward reduce the space in the thoracic outlet. This is a well-recognised contributing factor, especially together with tight scalene muscles or repeated overhead work.
A cervical rib is a small extra rib above the normal first rib, present from birth. Many people have one without any symptoms at all. It becomes a problem when it, along with other factors such as posture, narrows the thoracic outlet enough to compress nerves or vessels.
No. ScanAlign is a private self-pay clinic, and you can refer yourself. Your first step is a free video consultation, where a specialist discusses whether a scan is suitable for your symptoms.
EOS uses about 90% less radiation than a standard X-ray, around ten times less. This makes it one of the lowest-dose skeletal imaging options available.
EOS shows bones, joints and alignment clearly. For soft tissue detail, including the brachial plexus nerves and discs, MRI is usually the better tool. Your clinician may recommend both.
When you lie down, gravity is removed and the muscles relax. This can hide the postural patterns that narrow the thoracic outlet in daily life. A standing scan captures your skeleton while it bears your real weight, showing the alignment as it actually is when you are upright.
For neurogenic TOS, physiotherapy exercises that open the chest, stretch the scalenes and strengthen the upper back are often recommended as a first-line approach. Your physiotherapist will tailor the exercises to your specific findings.
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Could your posture be compressing a nerve?
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Book a free video consultationSources
- Illig KA, et al. Reporting standards of the Society for Vascular Surgery for thoracic outlet syndrome. Journal of Vascular Surgery, 2016;64(3):e23-e35.
- NHS. Thoracic outlet syndrome overview. nhs.uk (accessed 2024).
- Hooper TL, et al. Thoracic outlet syndrome: a controversial clinical condition. Journal of Manual & Manipulative Therapy, 2010;18(2):74-83.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.