Thoracic Outlet Syndrome

Populations and Risk Factors

• Women are affected approximately 3–4 times more frequently than men, likely due to narrower thoracic outlet anatomy and greater postural predisposition
• Peak incidence between ages 20 and 50; relatively uncommon in adolescents and the elderly
• Occupations or activities requiring sustained overhead arm positioning (painters, electricians, hairdressers, musicians, swimmers) — chronic scalene and pectoralis minor overuse
• Sedentary occupations with forward head posture and rounded shoulders (desk workers) — chronic scalene shortening and costoclavicular space narrowing
• Cervical rib present in approximately 0.5–1% of the population (bilateral in ~50% of those affected); an elongated C7 transverse process or fibrous band from C7 to the first rib produces the same mechanical effect
• History of clavicular fracture, first rib fracture, or whiplash injury — post-traumatic fibrosis or callus formation narrows the costoclavicular space
• Muscular hypertrophy of the scalenes (weight lifters, overhead athletes) or pectoralis minor
• Comorbidity with upper crossed syndrome, forward head posture, or cervical hyperlordosis

Causes and Pathophysiology

Three Compression Sites

The neurovascular bundle (brachial plexus + subclavian vessels) passes through three anatomical bottlenecks in sequence. Compression can occur at one or more sites simultaneously:

• Interscalene triangle: Bordered by the anterior scalene (anterior), middle scalene (posterior), and the first rib (inferior). The brachial plexus trunks and subclavian artery pass through this triangle; the subclavian vein passes anterior to the anterior scalene. Scalene hypertrophy or spasm narrows this space — the most common compression site in neurogenic TOS. A cervical rib or elongated C7 transverse process elevates the floor of the triangle, further narrowing the passage.
• Costoclavicular space: Between the clavicle (superior) and the first rib (inferior). Depression of the shoulder girdle (heavy carrying, poor posture, strap compression) narrows this space. Clavicular fracture callus or first rib anomalies also reduce clearance. This is the primary site for venous TOS (Paget-Schroetter syndrome) because the subclavian vein is compressed between the clavicle and the subclavius muscle/costoclavicular ligament.
• Retropectoralis minor space (subcoracoid space): The neurovascular bundle passes deep to the pectoralis minor as it attaches to the coracoid process. A shortened or hypertonic pectoralis minor compresses the bundle against the chest wall, particularly during arm abduction and external rotation. This site is assessed with Wright's test (hyperabduction).

Why the Medial Cord Is Most Vulnerable

The lower trunk (C8–T1) and its continuation as the medial cord occupy the most inferior position in the brachial plexus as it crosses the first rib. This means:

• The lower trunk is physically closest to the first rib and any cervical rib or fibrous band arising from C7 — it is the first structure compressed when the interscalene triangle narrows
• The medial cord gives rise to the ulnar nerve (pure medial cord) and the medial contribution to the median nerve — this explains the characteristic ulnar distribution of neurogenic TOS: medial forearm, ring and little fingers, intrinsic hand muscles
• The lateral and posterior cords are positioned more superiorly and are relatively spared in typical TOS; upper trunk involvement (C5–C6) producing shoulder and lateral arm symptoms is uncommon and suggests an alternative diagnosis

Scalene Hypertonia Mechanism

Forward head posture places the anterior and middle scalenes in a chronically shortened position. Chronic shortening produces:

• Increased resting tone and eventual fibrotic changes in the scalene muscles
• Narrowing of the interscalene triangle at rest, with further narrowing during cervical lateral flexion to the contralateral side or deep inspiration (scalenes are accessory muscles of respiration)
• Sustained low-grade compression of the lower trunk impairs intraneural microcirculation before producing frank axonal damage — this subthreshold compression is the basis of "disputed" or nonspecific neurogenic TOS, where symptoms are present but objective neurological findings are minimal

Axoplasmic Flow and the Double Crush Phenomenon

• Compression at any point along a peripheral nerve impairs axoplasmic transport — the bidirectional flow of proteins, organelles, and trophic factors within the axon
• When axoplasmic flow is impaired at the thoracic outlet (proximal site), the nerve becomes more vulnerable to a second compression at a distal site (carpal tunnel, cubital tunnel, or pronator teres)
• Clinically, patients with TOS have a significantly higher incidence of concurrent carpal tunnel syndrome and cubital tunnel syndrome — treatment of only the distal site produces incomplete or temporary relief because the proximal compression continues to impair nerve health
• This double crush mechanism also works in reverse: an existing distal entrapment can lower the threshold for symptomatic TOS at the thoracic outlet

Neurogenic vs. Venous vs. Arterial TOS

• Neurogenic TOS (~90% of cases): Subdivided into true neurogenic (objective findings on EMG/NCS — rare, ~1%) and disputed/nonspecific neurogenic (subjective symptoms with normal or equivocal electrodiagnostic testing — the vast majority). True neurogenic TOS shows measurable hand intrinsic muscle atrophy (thenar or hypothenar wasting), sensory loss in C8–T1 dermatome, and reduced ulnar SNAP amplitudes. Disputed neurogenic TOS presents with pain, paresthesia, and subjective weakness but without objective neurological deficit — this is the form most commonly seen in MT practice.
• Venous TOS (Paget-Schroetter syndrome, ~5%): Subclavian vein compression or thrombosis produces sudden unilateral upper extremity swelling, cyanotic discoloration, heaviness, and distended superficial veins across the shoulder and chest wall. Typically precipitated by vigorous repetitive overhead activity ("effort thrombosis"). This is a medical emergency requiring anticoagulation and possible thrombolysis. Do not treat — refer immediately.
• Arterial TOS (~1%): Subclavian artery compression produces pallor, coolness, diminished radial pulse, and digital ischemia (Raynaud-like symptoms) in the affected hand. Usually associated with a cervical rib or first rib anomaly compressing the artery. Embolic events can produce acute hand or digit ischemia. Do not treat — refer immediately.

Signs and Symptoms

Neurogenic TOS (Disputed/Nonspecific — Most Common Presentation)

• Pain: Aching or diffuse pain in the neck, shoulder, and medial arm/forearm; often poorly localized; may radiate to the hand in an ulnar distribution (ring and little fingers)
• Paresthesia: Numbness, tingling, or pins and needles in the medial forearm, ring finger, and little finger; frequently nocturnal (sleeping position compresses the outlet)
• Weakness: Subjective grip weakness and clumsiness; difficulty with fine motor tasks; dropping objects; hand fatigue with sustained gripping or overhead work
• Provocative pattern: Symptoms reproduced or worsened by sustained overhead arm positioning (blow-drying hair, painting overhead, reaching into high shelves), carrying heavy loads at the side, and sleeping with the arm overhead
• Postural association: Symptoms often correlate with forward head posture, rounded shoulders, and upper crossed syndrome; may worsen throughout the workday in desk workers

True Neurogenic TOS (Rare — Objective Findings)

• All symptoms of disputed neurogenic TOS plus:
• Visible muscle wasting: Thenar or hypothenar atrophy (Gilliatt-Sumner hand); interosseous muscle wasting
• Measurable weakness: Grip strength deficit; reduced finger abduction/adduction strength (ulnar nerve motor)
• Sensory loss: Objectively diminished sensation in C8–T1 dermatome (medial forearm, ring/little fingers) on formal sensory testing

Venous TOS (Paget-Schroetter Syndrome)

• Sudden onset unilateral upper extremity swelling and heaviness
• Cyanotic (bluish) discoloration of the hand and forearm
• Distended superficial veins visible across the shoulder and upper chest wall
• Typically follows vigorous repetitive overhead activity
• This is a medical emergency — refer for anticoagulation

Arterial TOS

• Pallor and coolness of the affected hand and digits
• Diminished or absent radial pulse (may be positional)
• Raynaud-like color changes (white → blue → red) in the digits
• Claudication-type pain with arm use
• Risk of digital embolization (acute blue/cold finger)
• This is a medical emergency — refer for vascular assessment

Assessment Profile

Subjective Presentation

• Chief complaint: "My arm goes numb when I raise it" or "I get tingling in my ring and little fingers"; difficulty blow-drying hair, reaching overhead, or sustained arm elevation; frequently reports dropping objects or subjective grip weakness; symptoms may be worse at night
• Pain quality: Aching, diffuse neck/shoulder/medial arm pain; superimposed sharp or burning paresthesia in the ulnar distribution (medial forearm, ring and little fingers); pain is often poorly localized compared to cervical radiculopathy, where it follows a clear dermatomal track
• Onset: Usually insidious; may follow a change in occupation or activity level (new desk job, new exercise routine); post-traumatic onset (whiplash, clavicular fracture) is less common but more specific; no single injury event in most cases
• Aggravating factors: Sustained overhead arm positioning (blow-drying, painting, stocking shelves); carrying heavy bags or backpacks; sleeping with arm above the head; prolonged computer use with poor ergonomics; deep breathing may worsen interscalene compression
• Easing factors: Lowering the arm to the side; postural correction (retracting the shoulders opens the costoclavicular space); shaking the hand out; changing sleeping position
• Red flags: Sudden unilateral arm swelling with cyanosis (venous TOS — emergency referral; do not treat); pallor, coolness, or absent radial pulse (arterial TOS — emergency referral; do not treat); progressive hand muscle wasting without pain (true neurogenic — refer for electrodiagnostic confirmation)

Observation

• Local inspection: In chronic true neurogenic TOS, visible thenar or hypothenar atrophy and interosseous wasting may be present (Gilliatt-Sumner hand); in venous TOS, unilateral swelling and cyanosis are visible; in the disputed form (most common), no visible local changes are expected — state this to demonstrate awareness
• Posture: Forward head posture and rounded shoulders are characteristic; elevated first rib on the affected side may be visible or palpable; protracted scapulae with shortened pectoralis minor; overall upper crossed syndrome pattern — these postural findings are both a cause and a perpetuating factor
• Gait: Not typically affected; omit from formal assessment unless concurrent lower extremity involvement suggests a systemic neurological condition

Palpation

• Tone: Anterior and middle scalene hypertonicity on the affected side — often fibrotic rather than acutely guarded in chronic presentations. Pectoralis minor tightness palpable as a shortened, taut band from coracoid process to ribs 3-5. Subclavius hypertonicity deep to the clavicle. Upper trapezius and levator scapulae compensatory hypertonia consistent with upper crossed syndrome pattern.
• Tenderness: Scalene muscles — tenderness at the lateral neck between the SCM and upper trapezius, particularly at their first rib attachments. Supraclavicular fossa tenderness or fullness. Pectoralis minor — tenderness at the coracoid process attachment and along the muscle belly toward ribs 3-5. Referred path tenderness: in neurogenic TOS with neural sensitization, tenderness may be traceable along the medial cord pathway — medial upper arm, medial forearm, and into the ring and little fingers. This maps the medial cord distribution described in Pathophysiology. Correlate with ULNT findings rather than interpreting as a local forearm or hand lesion.
• Temperature: Usually normal; in arterial TOS, coolness of the affected hand and digits is a significant finding requiring referral; assess radial pulse bilaterally — diminished pulse on the affected side, particularly with positional testing, suggests vascular component
• Tissue quality: Scalenes may be fibrotic and ropy in chronic cases; pectoralis minor often inelastic with reduced fascial mobility; active trigger points in scalenes refer pain to the chest, medial scapular border, and down the arm in a pattern that overlaps with TOS symptoms; first rib mobility may be restricted — reduced spring on PA pressure compared to contralateral side

Motion Assessment

• AROM: Cervical AROM may reproduce upper extremity symptoms — lateral flexion toward the affected side compresses the interscalene triangle; lateral flexion away stretches the scalenes and may also provoke; shoulder abduction and external rotation (overhead movements) are the most consistently provocative functional movements; full cervical ROM is often maintained but with symptom reproduction at end-range
• PROM / end-feel: Cervical PROM usually normal range with a firm muscular end-feel on lateral flexion — the restriction is symptomatic rather than mechanical; shoulder PROM is typically full (distinguishes TOS from shoulder pathology); first rib PROM assessed via PA spring test — restricted spring with a hard end-feel on the affected side suggests first rib elevation
• Resisted testing: Grip strength may be subjectively reduced but formal resisted testing is often normal in disputed neurogenic TOS; in true neurogenic TOS, weakness is specific to C8–T1 myotome — finger abduction (interossei, ulnar nerve), thumb opposition (opponens pollicis, median nerve contribution), grip strength; resisted cervical lateral flexion may reproduce symptoms by activating the scalenes

Special Test Cluster

Cluster interpretation: Roos (EAST) is the single most dependable test. A positive Roos with a positive Adson's localizes compression to the interscalene triangle; a positive Roos with a positive Wright's localizes to the pec minor space. A negative Spurling's with positive provocation tests supports TOS over cervical radiculopathy. A positive Phalen's alongside positive TOS tests raises the double crush possibility — both conditions may coexist.

Differential Diagnoses