What is Thoracic Outlet Syndrome (TOS) and
Thoracic outlet syndrome is one of the most underdiagnosed conditions in overhead athletes — and one of the most consequential when missed.
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Thoracic outlet syndrome (TOS) in a baseball player is rarely obvious, almost always delayed in diagnosis, and frequently mismanaged. Here's what you need to know:
- 1TOS is a compression syndrome, not a single diagnosis. The brachial plexus, subclavian artery, or subclavian vein can all be compressed in the thoracic outlet — and each presents differently.
- 2The average time to diagnosis is 3–7 years. Symptoms mimic cervical radiculopathy, rotator cuff pathology, and ulnar neuropathy — which is why it's almost always misdiagnosed first.
- 3Ulnar nerve transposition rarely solves the problem. If the compression is proximal — at the thoracic outlet — operating on the elbow is treating the wrong address.
- 4Physical therapy is the first-line treatment and is highly effective when TOS is caught early. However, a large number of cases require botox injections and/or surgery if there is a poor response to PT alone.
- 5Posture, scapular mechanics, and first rib mobility are the clinical targets. These are addressable. Knowing what to look for makes early intervention possible.
Your Athlete's Arm "Falls Asleep." Everyone Blames the Elbow.
It's a story I hear more often than I should. An athlete starts complaining about numbness and tingling in the ring and small fingers after any hard bout of exercises like throwing or playing tennis. Maybe there's some forearm heaviness, or a subtle loss of grip strength. The athletic trainer flags it. An orthopedic surgeon evaluates it. An EMG is ordered. The read comes back: ulnar nerve compression. A cubital tunnel release or ulnar nerve transposition is scheduled.
That's because in a significant subset of overhead athletes, the ulnar nerve symptoms are not coming from the elbow. They're coming from the neck — specifically from a region called the thoracic outlet, where the nerves and blood vessels that supply the arm pass through a narrow anatomical corridor between the collarbone, first rib, and surrounding musculature.
Thoracic outlet syndrome (TOS) is one of the most underdiagnosed conditions. It doesn't show up cleanly on MRI. It mimics a half-dozen other diagnoses. And by the time it's correctly identified, many athletes have already been through one or more failed interventions. That needs to change.
Anatomy, Presentation, and Why It's so Hard to Catch
What Is the Thoracic Outlet?
The thoracic outlet is a narrow passageway at the base of the neck and top of the chest. Running through it are the brachial plexus (the network of nerves that powers the entire arm), the subclavian artery, and the subclavian vein. When any of these structures gets compressed in this space — by muscle hypertrophy, a cervical rib, postural collapse, or repetitive overhead loading — you have thoracic outlet syndrome.
There are three distinct subtypes, and understanding which one you're dealing with completely changes the clinical picture:
Neurogenic TOS (nTOS)
Compression of the brachial plexus. By far the most common type — accounts for over 95% of TOS cases. Presents with numbness, tingling, and weakness in the arm and hand. Most commonly affects the ulnar distribution (ring and small finger), which is exactly why it gets mistaken for cubital tunnel syndrome.
Venous TOS (vTOS)
Compression of the subclavian vein. Presents with arm swelling, heaviness, and a bluish discoloration of the hand and forearm. Known as Paget-Schroetter syndrome when it causes axillary-subclavian vein thrombosis — a blood clot that is a medical emergency in a throwing athlete.
Arterial TOS (aTOS)
Compression of the subclavian artery. The rarest but most dangerous type. Presents with a cold, pale, or painful hand, diminished radial pulse, and in severe cases, distal embolism. Requires urgent vascular surgical evaluation.
Why Throwers Are Uniquely at Risk
Repetitive overhead throwing generates significant hypertrophy of the scalene muscles and pectoralis minor — two primary compressive structures at the thoracic outlet. Combined with postural changes from years of throwing, this creates a chronically narrowed outlet in a population that uses their arm at extreme ranges hundreds of times per outing.
How TOS Presents in the Clinic
- 1Numbness and tingling in the ring and small finger during or after throwing — often described as the arm "falling asleep"
- 2Forearm heaviness or fatigue that sets in earlier than expected in a bullpen or game — the athlete may describe losing feel for the ball
- 3Grip weakness on the throwing side, occasionally noted as difficulty with everyday tasks like opening jars
- 4Symptoms that are position-dependent — worse with the arm elevated overhead, better with the arm at the side
- 5Neck and shoulder aching that is diffuse and hard to localize — athletes often describe it as general tightness rather than sharp pain
- 6In venous TOS: visible arm or hand swelling after throwing, prominent superficial veins across the chest and shoulder
Why Does It Take So Long to Diagnose?
The diagnostic delay in TOS is well-documented in the literature and remains one of the most frustrating aspects of managing this condition. Research consistently shows an average diagnostic delay of 3 to 7 years from symptom onset to correct diagnosis. Several structural problems drive this:
- 1No definitive imaging test. Standard MRI and X-ray are largely unreliable for neurogenic TOS. The diagnosis is primarily clinical — made through history, physical examination, and provocative testing — which requires a clinician who is specifically looking for it.
- 2EMG/NCS studies are frequently normal. Electrodiagnostic testing is notoriously insensitive for neurogenic TOS. A normal EMG does not rule out TOS — yet a normal result often closes the clinical investigation prematurely.
- 3Symptom overlap with common diagnoses. Ulnar nerve compression at the elbow, cervical radiculopathy at C8-T1, rotator cuff pathology, and medial epicondylitis all share overlapping symptom profiles with neurogenic TOS. The path of least resistance is to treat the more common diagnosis first.
- 4Low clinical awareness. TOS is not commonly emphasized in standard orthopedic or sports medicine training curricula. Many clinicians working with throwing athletes have never performed a structured TOS evaluation.
The Ulnar Nerve Transposition Problem
When a pitcher presents with ulnar-distribution numbness and tingling, the reflexive workup leads to an elbow evaluation. In my clinical experience, I rarely see ulnar nerve transpositions resolve symptoms when TOS is the underlying driver. When the compression is occurring proximally — at the scalene triangle or costoclavicular space — surgically repositioning the ulnar nerve at the elbow does nothing to address the actual source of nerve irritation. The athlete wakes up from surgery with the same symptoms, now also carrying surgical recovery time and scar tissue at the elbow. These decompressions and transpositions have their place - but IMO, TOS needs to be ruled out first.
Before any ulnar nerve surgery is scheduled in a throwing athlete, TOS must be ruled out through a structured clinical examination. The two conditions can coexist but operating on the distal site without addressing the proximal compression first is a setup for a poor outcome.
What the Literature Tells Us — and What It Still Can't Agree On
Published data consistently documents an average diagnostic delay of 3 to 7 years for neurogenic TOS. Studies cite the primary drivers as normal electrodiagnostic results, symptom overlap with cervical and elbow pathology, and low clinical suspicion among treating providers. In overhead athletes specifically, the throwing-position provocation of symptoms adds complexity that standard orthopedic evaluations are not designed to capture.
Multiple studies have confirmed that standard nerve conduction studies and EMG have poor sensitivity for neurogenic TOS — with some estimates as low as 50–77% sensitivity depending on severity. Relying on a normal EMG to exclude TOS in a symptomatic overhead athlete is clinically insufficient. The diagnosis requires structured provocative testing and clinical reasoning, not electrodiagnostics alone.
Venous TOS resulting in effort-induced axillary-subclavian vein thrombosis has been specifically documented in competitive baseball players. Case series and vascular surgery literature identify repetitive overhead loading as the primary mechanical driver. Early anticoagulation followed by thrombolysis and first rib resection is the accepted treatment protocol, with outcomes significantly better when intervention occurs within the first 2 weeks of thrombosis.
Conservative management with targeted physical therapy has demonstrated meaningful symptom reduction in neurogenic TOS, particularly when treatment focuses on scalene flexibility, first rib mobilization, scapular stabilization, and postural correction. Studies report that 50–90% of patients with neurogenic TOS can achieve satisfactory outcomes with conservative care alone when the diagnosis is made early and the program is appropriately designed.
There is currently no single imaging study or electrodiagnostic test that reliably confirms neurogenic TOS. The diagnosis is clinical. That means it lives or dies on the quality of the evaluation. A clinician who may not see this all that often may miss signs of TOS — and the athlete will continue to be treated for the wrong diagnosis.
From Missed Diagnosis to Early Intervention: A Practical Framework
How to Catch It Earlier: Red Flags Every Coach and Clinician Should Know
🚩 Red Flags That Should Trigger a TOS Evaluation
- 🔴Ring and small finger numbness or tingling that occurs during or after throwing — especially if it comes on earlier as the season progresses
- 🔴Arm heaviness or early fatigue that the athlete describes as the arm "dying" mid-outing
- 🔴Visible arm or hand swelling after a throwing session — venous TOS red flag, warrants urgent vascular evaluation
- 🔴A cold, pale, or mottled hand after throwing — arterial TOS red flag, requires same-day evaluation
- 🔴Grip weakness on the throwing side without a clear structural explanation at the elbow or wrist
- 🔴Symptoms consistently worse with the arm overhead and consistently better with the arm at the side
The Provocative Tests Worth Knowing
| Test | What It Does | Positive Finding |
|---|---|---|
| Adson's Test | Compresses the scalene triangle by extending and rotating the neck while the patient inhales | Diminished radial pulse or reproduction of symptoms |
| Roos Test | Arms abducted 90°, elbows flexed 90°, patient opens and closes hands for 3 minutes | Reproduction of symptoms or inability to complete 3 minutes — highly specific for TOS in throwers. Perofrm strength test for ER and ABD before and after - a 20% reduction may indicate TOS is present (anecdotally) |
| Upper Limb Tension Test | Neural tension test for brachial plexus sensitization | Symptom reproduction with arm positioning that loads the neural structures |
| Tinel's Sign | light percussion (tapping) over the scalene and pec minor | induces a tingling or "pins and needles" sensation (paresthesia) in the distal distribution of that nerve, signaling nerve compression/involvement |
Treatment: What Works and When
- ✓Physical Therapy (First Line for Neurogenic TOS) — A structured PT program targeting scalene flexibility, first rib mobilization, scapular upward rotation, thoracic extension mobility, rotator cuff strengthening, and postural retraining. This is the foundation of conservative care. When the diagnosis is made early and the program is well-designed, the majority of athletes can return to throwing without surgical intervention.
- ✓Botox Injections into the Anterior Scalene (Second Line) — When PT alone is insufficient, image-guided botulinum toxin injections into the anterior and/or middle scalene muscles can temporarily reduce compressive force on the brachial plexus, providing a window for more effective physical therapy. This is a well-established adjunct in the TOS literature with meaningful short-term benefit in athletes who plateau with conservative care.
- ✓Surgery (Reserved for Refractory Cases and Vascular TOS) — First rib resection, with or without removal of scalene and pec minor musculature, is the surgical standard for TOS that fails conservative management. For venous TOS with thrombosis, catheter-directed thrombolysis followed by first rib resection is the protocol — timing is critical, as outcomes deteriorate rapidly beyond the first two weeks after clot formation. Arterial TOS requires urgent vascular surgical referral.
- ✗Ulnar Nerve Transposition Without TOS Workup — Do not proceed to ulnar nerve surgery in a throwing athlete with ring and small finger symptoms until TOS has been formally evaluated and excluded. Operating on the elbow when the compression is proximal will not resolve symptoms and adds unnecessary surgical risk and recovery time.
If your pitcher is complaining of hand numbness, arm heaviness, or early fatigue that persists despite prior treatment — push for a TOS-specific evaluation before consenting to any elbow surgery. Ask your clinician directly: "Has thoracic outlet syndrome been ruled out?"
© Anthony Videtto, DPT · avbaseballperformance.com · This content is for educational purposes and does not constitute individualized medical advice.
