Thoracic outlet syndrome (TOS) is a condition where nerves or blood vessels get compressed in the narrow space between your collarbone and first rib. This passageway, called the thoracic outlet, is crowded with important structures: a bundle of nerves that controls your arm and hand, plus major arteries and veins. When any of these get squeezed by bone, muscle, or scar tissue, the result is pain, numbness, swelling, or weakness that radiates from your neck and shoulder down into your arm and fingers.
There are three types, defined by which structure is compressed. The nerve-related form accounts for the vast majority of cases, while vascular forms involving veins make up 3% to 5% and the arterial form represents roughly 1%.
The Three Types of TOS
Neurogenic TOS
This is by far the most common form. It happens when the brachial plexus, the network of nerves running from your neck into your arm, gets compressed in the thoracic outlet. People with neurogenic TOS often notice numbness or tingling in their fingers, particularly the ring and pinky fingers, because the lower portions of the nerve bundle are usually affected more than the upper portions. Over time, the small muscles at the base of your thumb can waste away, making it harder to grip objects. Athletes sometimes describe difficulty holding a racket or ball.
Neurogenic TOS also has a “disputed” or nonspecific subtype, which is a source of real frustration for patients and doctors alike. These cases involve diffuse pain across the arm, shoulder blade, and neck without clear-cut nerve findings on testing. The pain is real, but it doesn’t follow a neat pattern, which can make diagnosis slow.
Venous TOS
Also called Paget-Schroetter syndrome, this form occurs when one or more veins under the collarbone are compressed and damaged, sometimes leading to a blood clot. It’s closely linked to repetitive overhead arm motions, which is why it’s sometimes called “effort thrombosis.” Symptoms typically affect one arm and include swelling, a feeling of heaviness, aching, and a bluish or purplish discoloration of the skin. You may also notice visible veins across your shoulder, arm, or one side of your chest as blood reroutes around the blockage.
Arterial TOS
The rarest form, arterial TOS, involves compression of an artery under the collarbone. It’s the most dangerous type because restricted arterial flow can lead to serious complications in the hand and fingers. Patients with arterial TOS often require surgery rather than conservative treatment.
What Causes the Compression
The thoracic outlet is already a tight space, so anything that narrows it further, even slightly, can trigger symptoms. Causes fall into two broad categories: anatomical variations you’re born with and things that happen over the course of your life.
The most well-known anatomical variation is a cervical rib, an extra rib that grows from the neck portion of the spine. Between 1% and 3% of the population has one, though only a small fraction of those people ever develop TOS. A cervical rib can extend down to connect with the first rib or be only partially formed, but either way it crowds the outlet and increases the chance of nerve or blood vessel compression. Other congenital factors include an abnormally shaped first rib, an unusual collarbone, or an extra scalene muscle in the neck.
Acquired causes are more common overall. Whiplash injuries, car accidents, falls, and other trauma to the neck and shoulder can produce scar tissue or swelling that compresses the outlet. Repetitive overhead motions from sports like swimming or volleyball, or from occupations that involve sustained arm elevation, gradually strain the area. Bodybuilding is another recognized trigger, as heavily developed neck and chest muscles can tighten the space.
How It Feels Day to Day
Neurogenic TOS tends to build gradually. You might first notice tingling or numbness in your hand after sleeping with your arm overhead or after a long stretch of working at a computer. Over weeks or months, pain may spread across the neck, shoulder, and down the arm. Some people develop a dull ache behind the collarbone or between the shoulder blades. Activities that involve reaching overhead or carrying heavy bags often make symptoms worse. In advanced cases, hand weakness becomes noticeable, particularly with fine motor tasks like buttoning a shirt.
Venous TOS, by contrast, can come on suddenly. Your arm may swell noticeably after vigorous activity, turn dusky in color, and feel heavy or tight. This is a more urgent presentation because it can signal a blood clot that needs prompt treatment.
How TOS Is Diagnosed
Diagnosing TOS, especially the neurogenic form, can be a long process. There’s no single definitive test. Doctors typically start with a physical exam that includes provocative maneuvers designed to reproduce your symptoms by putting pressure on the thoracic outlet. You might be asked to turn your head, raise your arms, or hold your arms in a specific position for a sustained period to see if numbness, tingling, or pulse changes occur.
One classic exam finding in neurogenic TOS is visible wasting of the muscle at the base of the thumb, with lesser involvement of the small muscles between the fingers. This pattern, known as the Gilliatt-Sumner hand, is a strong indicator, but it’s only present in more advanced cases. Imaging studies like ultrasound, CT, or MRI can reveal structural causes such as a cervical rib. Nerve conduction studies help rule out other conditions like carpal tunnel syndrome. For vascular TOS, specialized imaging that maps blood flow through the vessels while your arms are in different positions is particularly useful.
Conservative Treatment
Most people with neurogenic TOS start with physical therapy, and many improve enough to avoid surgery. The goal is to open up the thoracic outlet by improving posture, stretching tight structures around the neck and chest, and strengthening the muscles that hold the shoulder blade in a better position.
A typical exercise program includes:
- Chin tucks: Lying on your back with a rolled towel under your neck, you gently nod your chin toward your throat while keeping the back of your head on the floor. This helps correct forward head posture that narrows the outlet. Hold for about 6 seconds, 8 to 12 repetitions.
- Shoulder blade squeezes: Sitting or standing with arms relaxed at your sides, you squeeze your shoulder blades down and together. This strengthens the muscles that pull the shoulders back and away from the compressed area. Hold for 6 seconds, 8 to 12 repetitions.
- Chest and shoulder stretches: Lying on your back with knees bent, you move your arms through a series of positions, from resting at your sides with palms up, to a T shape, to a goalpost shape with elbows bent at 90 degrees, to fully overhead. Each position is held for 15 to 30 seconds, stretching the front of the chest and shoulder progressively.
Consistency matters more than intensity. These exercises work by gradually retraining the muscles and tissues around the thoracic outlet over weeks to months. Your physical therapist will likely add additional stretches and nerve-gliding techniques based on your specific symptoms.
When Surgery Becomes Necessary
Surgery is considered when several months of physical therapy haven’t provided enough relief, or when the vascular forms of TOS require structural correction. Arterial TOS in particular often goes straight to surgical intervention because of the risk of serious complications.
The most common procedure is resection of the first rib along with removal of the scalene muscles at the front of the neck. This creates permanent additional space in the thoracic outlet. The surgeon makes a small incision behind and parallel to the collarbone, removes the first rib and any scar tissue or abnormal bands compressing the area, and carefully protects the nerves and blood vessels. A typical hospital stay is about two nights for pain management and monitoring.
Outcomes are generally favorable. A Johns Hopkins study of 208 patients who underwent first rib resection for neurogenic TOS found that the median patient reported 80% improvement in their preoperative symptoms. The research team used this 80% threshold as their benchmark for a good surgical outcome. For vascular TOS, surgery may also involve repairing damaged veins or arteries and treating any blood clots.
Recovery after surgery involves gradually returning to normal activities over several weeks, with physical therapy to rebuild shoulder and arm strength. Most people can return to desk work within two to three weeks, though full recovery from physically demanding jobs or sports takes longer.