Thoracic outlet syndrome

Key points

Reporting standards from 2016 and a 2022 consensus describe thoracic outlet syndrome as a group of disorders of compression at the thoracic outlet^1,2. In plain terms, nerves or blood vessels are squeezed between the base of the neck and the armpit.
It has nerve, vein and artery forms¹. A 2022 consensus calls the nerve (neurogenic) form the most frequent, at 39% to 95% of cases in the literature².
A 2014 review was hampered by the lack of accepted criteria, and a 2022 consensus found no classification shared across specialties^2,3.
The 2022 consensus estimates that 10 in 100,000 people have it, perhaps many more among athletes, with four women affected for every man².
In one trial of 50 people with the nerve form, assigned by chance to each group, disability scores at three months were lower after surgery than with continued non-surgical care⁴. Every person in that group then applied for surgery, after which the groups no longer differed⁴.

What it is

How sources define it

Reporting standards from the Society for Vascular Surgery in 2016 call the syndrome a group of disorders sharing compression at the thoracic outlet¹. A 2022 consensus of European nerve surgeons, built on a systematic search of the literature, adds the cause². In its account, bone, muscle or fibrous tissue presses on the bundle of nerves and blood vessels there². Both name three structures at risk^1,2:

the brachial plexus, the network of nerves, starting at the neck, that serves the arm²;
the subclavian artery, the large artery that runs beneath the collarbone²;
the subclavian vein, the large vein that runs beneath the collarbone².

The 2016 standards name a neurogenic (nerve), a venous and an arterial form after these, and say the forms can coexist¹.

Three places the squeeze can happen

The 2022 consensus names three spaces where narrowing can cause the syndrome²:

the interscalene triangle, bounded by the anterior and middle scalene muscles at the side of the neck and by the first rib²;
the costoclavicular space, the gap between the collarbone and the first rib²;
the space beneath the pectoralis minor, a smaller chest muscle beneath the pectoralis major².

According to the consensus, the brachial plexus and the subclavian artery run through the triangle between the scalenes². The subclavian vein runs in front of the anterior scalene instead².

Engraving of the front of the neck vertebrae with the throat and jaw removed, from the base of the skull at the top down to the third thoracic vertebra and the first two ribs. Close against the vertebrae on each side lies the longus colli, labelled with its upper oblique, vertical and lower oblique parts. The longus capitis runs up from the side of the neck vertebrae to the basilar part of the occipital bone, and the small rectus capitis anterior and rectus capitis lateralis sit at the very top between the atlas and the skull. The scalene muscles run from the sides of the vertebrae down to the first and second ribs. — The deep muscles on the front of the neck vertebraeHenry Vandyke Carter, in Henry Gray, Anatomy of the Human Body (1918), Fig. 387. Public domain, via Wikimedia Commons. (source, Public domain)

Squeezing beneath the pectoralis minor has its own page, pectoralis minor syndrome. A 2022 review calls it the dominant cause of the neurogenic form⁵. A 2017 review describes squeezing above and below the collarbone as two conditions that often occur together⁶.

The three forms

Form	How sources describe it	Share of cases
Neurogenic	The most frequent type, in a 2022 consensus²	39% to 95% in the literature²
Venous	Can lead to clots in arm veins in 10% to 20% of cases, in a 2022 review of sport⁷	About 5% to 10%⁷
Arterial	An artery squeezed by an anatomical abnormality, usually in younger people, in a 2024 review⁸	Rare, 1% to 19%, mostly with cervical ribs²

The 2022 review of sport names the venous form’s sudden complication Paget-Schroetter syndrome⁷. A clot in the arm veins can sometimes lead to a pulmonary embolism, a clot that blocks an artery in the lungs⁷. A 2020 review calls Paget-Schroetter syndrome a rare clot in the vein of the armpit and below the collarbone⁹.

Where definitions disagree

Sources do not agree on how to define or classify the syndrome, especially its neurogenic form^2,3.

2016 standards. The neurogenic form counts as present when three of four criteria are met, including a positive response to a scalene test injection¹.
“Disputed” cases. Vascular surgery standards advise against the term, the 2022 consensus reports, but most neurologists still split the neurogenic form into true and disputed types².
A new split. The 2022 consensus proposes one neurogenic type with weakness or wasting of arm muscles, and others with mainly pain or sensory symptoms².
Adapted criteria. A 2024 Delphi study of 21 hand surgeons, which polled them in rounds to work toward agreement, recommends an adapted version of the 2016 criteria¹⁰.

A 2014 Cochrane review, a systematic review done to the Cochrane Collaboration’s published standards, called for an agreed definition³.

Why it is hard to pin down

The 2022 consensus reports that tests holding the arm in set positions have a sensitivity of 72% and a specificity of 53%². That is, they picked up 72% of cases but correctly cleared 53% of people without the syndrome². The consensus calls identifying and classifying it a challenge².

In a records review of 41 people with artery compression at the outlet, two-thirds had long-standing symptoms hard to tell from nerve compression¹¹. Of 23 whose symptoms suggested nerve compression alone, 13 had a significant artery abnormality¹¹.

Who it affects

How common it is

Estimates vary widely^2,7. Prevalence is the share of people who have a condition at a given time; incidence is how many new cases appear over a set time.

Who was studied	What was found
People generally, in the 2022 consensus	Prevalence estimated at 10 per 100,000 people, perhaps much higher in athletes²
The general population, in a 2022 review of sport	Incidence hard to judge, probably about 3 to 80 cases per 100,000 people⁷
526 people referred to one centre	Neurogenic form estimated at 2 to 3 new cases per 100,000 people a year, much lower than earlier estimates¹²
The same 526 people	Venous form estimated at 0.5 to 1 case per 100,000 people a year; arterial form sporadic¹²

Sex, age and extra ribs

Sex. The 2022 consensus reports the syndrome as four times more common in women than in men².
Age. A 2022 review of sport gives mean ages in the general population, not in athletes⁷. These are 20 to 30 for the vascular forms and 30 to 40 for the neurogenic form⁷.
Children. A 2024 meta-analysis, which pools several earlier studies, covered six studies (216 patients)¹³. It found the syndrome more common in girls, and the neurogenic form a smaller share than in adults¹³.
Cervical ribs. These ribs of the neck occur in 0.5% to 2% of people, and 5% to 10% of those with them develop the syndrome².

Athletes

The 2022 review of sport reports that sports with repeated overhead arm motion and arm strength seem to be the most described⁷. Most of its case reports were of swimmers and baseball pitchers⁷. Citing case reports, the review states that strength training seems to be a risk factor in itself, while stressing that the syndrome is rare⁷. Quoting a 2010 source, it reports that 60% to 80% of people with Paget-Schroetter syndrome described intense upper-arm training in the days before the clot⁷. A 2020 review of 123 published cases of Paget-Schroetter syndrome in athletes found baseball (26.8%) and weightlifting (19%) the sports most often reported⁹.

What studies found

Surgery or non-surgical care for the nerve form

The authors of the STOPNTOS trial state that solid evidence for surgery on the neurogenic form was lacking before their trial⁴. Their trial, at one centre and not blinded, took 50 people who had not responded to non-surgical care⁴. It compared decompression through the armpit, surgery that takes pressure off a nerve, with continued non-surgical care⁴.

At three months, mean disability scores were 45 after surgery and 65 without⁴. The scores came from the DASH, a questionnaire that scores disability of the arm, shoulder and hand⁴. Every person in the non-surgical group then applied for surgery, after which the groups no longer differed⁴.

A prospective study follows people forward in time. In one such study of 150 people with the neurogenic form, all began with a six-week course of non-surgical care¹⁵. Afterwards, 27% improved enough to continue with that care alone, 60% had surgery and 13% declined further care or follow-up¹⁵. QuickDASH scores, from a shorter version of the DASH, fell by a mean 29.5% with that care alone and 47.9% with surgery¹⁵. No factors clearly predicted who would do well with that care alone¹⁵.

Comparing operations for the nerve form

Reviews and one recent trial compared operations with each other^3,16.

Study	What it found
One trial of 55 people with the “disputed” type, in the 2014 Cochrane review	Removing the first rib through the armpit eased pain more than a nerve operation above the collarbone; the evidence was very low quality³
A 2019 meta-analysis	Pooled success of 76% and 77% for two first rib removals, one adding scalene removal, and 85% for an operation leaving the rib¹⁷
A 2023 meta-analysis of 22 articles	Larger DASH gains and fewer complications after scalene surgery that left the rib than after first rib removal¹⁸
A 2025 meta-analysis of 18 studies	Excellent or good results in 71% after scalene surgery that left the rib; most studies used unvalidated measures¹⁹
A 2025 randomised trial of 48 women	Pain and numbness fell after two first rib operations, called resection and avulsion, with no significant difference between them¹⁶

The 2014 Cochrane review found no randomised evidence that either operation in its trial was better than no operation³. In the 2024 Delphi study, there was no agreement on routinely removing the first rib; 13 of 21 surgeons did not¹⁰.

Botulinum toxin injections

Botulinum toxin is a drug that weakens or relaxes a muscle it is injected into. The Cochrane review’s one trial of it, Finlayson 2011, randomised 38 people with the syndrome to injections into the scalene muscles³. The trial’s report found no clinically or statistically significant gain over a placebo, a dummy injection of saline, in pain, tingling or function²⁰. The Cochrane review’s own calculation found a significant fall in tingling at six months, but not in pain³.

Allergan Inc gave the trial a grant and the study drug, the review states³. It had also paid the authors about 10,000 Canadian dollars for training doctors in the toxin’s use³. The review states that Allergan had no role in the trial’s design or reporting³.

A 2023 systematic review, a set, checkable search and summary of the research, covered 10 studies (555 patients)²¹. For the neurogenic form, it found no evidence for the toxin as a validated option²¹. The pectoralis minor syndrome page sets out the trial’s figures and further reviews²².

The venous and arterial forms

Reviews of Paget-Schroetter syndrome found no randomised trials and no agreed best approach^23,24. A 2021 meta-analysis of 25 studies, none of them randomised, made one comparison in a subgroup of 20 studies²³. There, first rib removal was linked with better symptom resolution than clot-dissolving drugs alone²³. A 2023 meta-analysis of 60 reports rated the certainty of its evidence very low²⁴. In it, symptoms persisted in 46% given blood thinners alone, and in 4% given clot-dissolving drugs then first rib removal²⁴.

For the arterial form, a 2024 review states that people usually need an operation that includes at least first rib removal⁸. It describes outcomes as typically excellent, although people whose clots have travelled to the hand may need a finger amputated⁸.

Return to sport

Several series followed athletes after surgery for the syndrome^25,26,27:

Who was studied	What was reported
26 Major League Baseball pitchers who had a rib removed, found through public injury reports²⁵	81% returned to play after a mean 10 months²⁵
79 overhead athletes after first rib removal	97% returned to play and 81% to the same level²⁶
60 athletes aged 13 to 19	94.4% of the venous and 73.9% of the neurogenic group returned, not a statistically significant difference²⁷

In a US college database, 96% of 76 athletes with the syndrome were managed without surgery²⁸. Of these, 80.6% returned to full competition, as did 89.9% of those operated on²⁸. The 2022 review of sport found no long-term study of athletes after surgery⁷.

Connections

The pectoralis minor syndrome page covers squeezing below the collarbone, beneath the chest muscle⁶. A 2022 review there says nerve symptoms were once put down to squeezing between the scalenes, or between the clavicle (collarbone) and first rib⁵.

The axillary nerve is one of the five end branches of the brachial plexus²⁹. A stinger is a short-lived nerve injury of the brachial plexus or of neck nerve roots, in one study’s description³⁰. The seven cervical vertebrae are the bones of the neck³¹.

A 2026 scoping review, which maps the research on a topic, found stretching common in non-surgical programmes for the neurogenic form³². The scalene and chest muscles were the main targets³². The doorway pec stretch page reports studies of chest stretching, including one of eight weeks in 81 active people³³.