Thoracic outlet syndrome (TOS) is a condition where nerves, arteries, or veins get compressed in the narrow space between your collarbone and first rib as they pass from your neck toward your arm. This compression causes pain, numbness, tingling, or weakness that typically radiates into the shoulder, arm, and hand. It affects roughly 2 to 3 people per 100,000 each year for the nerve-related type, with vascular forms being even rarer.
Where the Compression Happens
The nerves and blood vessels that supply your arm travel through three tight spaces on their way from the neck to the armpit. The first and most common site of compression is a small triangle formed by two neck muscles (the scalenes) and the top of the first rib. This space contains the major nerve bundle for the arm, called the brachial plexus, along with the artery that feeds the arm.
The second space sits between the collarbone, first rib, and shoulder blade. The third is tucked beneath a bony point on the shoulder blade, just under a chest muscle. Any of these three passages can narrow enough to squeeze the nerves or vessels running through them, but the scalene triangle in the neck is where trouble starts most often.
Three Types of TOS
TOS is classified by which structures are being compressed, and the type determines both the symptoms and severity.
Neurogenic TOS is by far the most common form. It involves compression of the brachial plexus nerves and accounts for the vast majority of cases. Symptoms include movement-related pain (especially when lifting the arm overhead or pulling it backward), tingling, numbness, and a subjective sense of weakness. Pain shows up in 73 to 90 percent of patients, tingling in 32 to 98 percent, and numbness in 42 to 80 percent. Sensory symptoms hit the hand or fingers in virtually all cases but often spread up the arm, into the shoulder, and sometimes into the neck or head. In severe, long-standing cases, the small muscles of the hand can visibly waste away, a pattern sometimes called a Gilliatt-Sumner hand.
Venous TOS occurs when the vein draining the arm is compressed or develops a clot, often from repetitive overhead motions. This is sometimes called effort thrombosis or Paget-Schroetter syndrome, and it’s a form of deep vein thrombosis in the upper body. The arm may swell, turn bluish, and feel heavy. It affects roughly 0.5 to 1 person per 100,000 per year.
Arterial TOS is the rarest and most dangerous type. It involves compression of the artery supplying the arm, which can lead to reduced blood flow, coldness in the hand, or in serious cases, blood clots that threaten the limb. Arterial TOS is sporadic and almost always tied to a structural abnormality like an extra rib.
Common Causes and Risk Factors
TOS can develop from anatomical variations you’re born with, from injuries, or from repetitive strain. Often it’s a combination.
A cervical rib, an extra rib that grows from the neck portion of the spine, is one of the best-known structural risk factors. Between 1 and 3 percent of the population has one, though only a small fraction of those people develop TOS. The extra rib, or the fibrous bands attached to it, takes up space in an already tight corridor and increases the chance of compression.
Trauma is another major trigger. Whiplash injuries, falls, or repetitive overhead motions (common in certain sports and occupations like swimming, baseball, painting, or assembly-line work) can cause the scalene muscles to tighten or scar, narrowing the space around the nerves and vessels. Bodybuilding is also a recognized cause, as enlarged muscles can crowd the thoracic outlet. Poor posture, particularly a rounded upper back and forward-slumping shoulders, contributes by changing how the collarbone and first rib sit relative to each other.
How TOS Is Diagnosed
Diagnosing TOS, particularly the neurogenic type, can be frustrating. There’s no single definitive test, and symptoms overlap with conditions like carpal tunnel syndrome, cervical disc problems, and rotator cuff injuries.
Clinicians typically start with physical examination maneuvers designed to reproduce symptoms by putting the thoracic outlet under stress. These provocative tests have an average sensitivity of about 72 percent and specificity of only 53 percent, meaning they catch most cases but also produce a fair number of false positives. The Adson test and hyperabduction test tend to perform better, with positive predictive values around 85 and 92 percent respectively.
Imaging depends on which type of TOS is suspected. For neurogenic TOS, MRI of the chest is the preferred study, sometimes paired with a plain chest X-ray to look for a cervical rib. For venous TOS, ultrasound and CT with contrast are typically used to visualize clots or vein compression. Arterial TOS calls for CT angiography or MR angiography to map the blood vessels. Nerve conduction studies can help in some cases but are often normal in milder neurogenic TOS, which adds to the diagnostic challenge.
Physical Therapy and Conservative Treatment
For neurogenic TOS, the first-line approach is physical therapy, typically tried for four to six months before surgery enters the conversation. The goals are straightforward: improve posture, loosen the muscles that narrow the thoracic outlet, and strengthen the muscles that keep the shoulder blade in proper position.
The scalene muscles in the neck attach to the first rib and can lift it upward, squeezing the outlet. Stretching and mobilizing these muscles is a core part of treatment. Therapists also work on the thoracic spine, using hands-on mobilizations to reduce the rounded-back posture that contributes to compression. Strengthening focuses on the middle and lower trapezius and the serratus anterior, muscles that stabilize the shoulder blade and help open up the space beneath the collarbone.
For people who respond well, a gradual return to normal activity or sports can begin within four to six weeks, depending on progress. If soft tissue tightness is a major factor, manual therapy and targeted stretching can meaningfully improve posture and reduce symptoms even before strength fully returns.
When Surgery Is Needed
If conservative treatment fails after several months, or if the problem is vascular (involving arteries or veins), surgical decompression becomes the main option. The two most common procedures are first rib resection, where part of the first rib is removed to widen the passage, and scalenectomy, where the scalene muscles are partially cut to relieve pressure.
Initial surgery relieves symptoms in most patients, but recurrence is a real possibility. Between 15 and 20 percent of patients who undergo first rib resection or scalenectomy develop recurring symptoms over time. Long-term data shows that after the initial procedure, the success rate at five to ten years settles around 69 percent. Reoperation can improve that figure to the mid-80s.
Complications from surgery are relatively uncommon but worth knowing about. Temporary nerve injury to the arm occurs in less than 1 percent of cases. Temporary weakness of the diaphragm on the operated side, caused by irritation of the nerve that controls it, happens in about 4 percent, and becomes permanent in roughly 1.5 percent.
For venous TOS involving a clot, treatment often combines clot-dissolving therapy with surgical decompression to prevent the clot from returning. Arterial TOS, being the most dangerous form, almost always requires surgical repair to restore blood flow and remove the source of compression.