Thoracic Outlet Syndrome (TOS) is a fairly rare condition that afflicts the nerves and blood vessels as they travel down from the neck into the arm. For a period of time, it appeared that the Rangers and the Tigers had the market cornered for TOS cases, as Kenny Rogers, John Rheinecker, Jeremy Bonderman, Hank Blalock, and Matt Harrison all came down with TOS diagnoses. In effect, they were the lucky ones, because they were able to get accurate diagnoses, which can be difficult at times. Players with TOS can suffer through periods of pain, discomfort, or neurologic symptoms without an accurate diagnosis, and as a result, their performance suffers. Even with an accurate diagnosis, it’s not a given that they will return to pre-injury levels.

TOS was first described in the late 1800s, and variations continued to be discovered in the following decades. TOS can be broken down into three different types: arterial, venous, and neurogenic, all of which we can see examples of in baseball. Abduction, external rotation, cervical lateral flexion, and cervical rotation—which, of course, we see with every pitch—can contribute to baseball players developing subtypes of TOS.

Anatomy and Variants
The space that forms the thoracic outlet is created by the clavicle, first rib, costoclavicular ligament, anterior scalene muscle, and subclavius muscle. The neurovascular bundle is composed of the brachial plexus, subclavian artery, and subclavian vein. A rib coming off of the last cervical vertebrae (C7) is a congenital variant that is found in anywhere from 0.5 to one percent of the population. Half of those few have the rib bilaterally. This cervical rib can predispose an athlete to all three types of TOS and is a common finding in surgical cases of TOS.

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TOS encompasses a variety of symptoms. Generally, the definition of TOS includes symptoms in the upper extremity related to compression on the nerves, artery, or vein in the thoracic outlet space just above the first cervical rib. Symptoms guide the clinical assessment, and diagnostic studies are then used to confirm the clinical suspicion.

Causes and Presentation
The causes of TOS vary as much as the classifications do. Arterial TOS involves the subclavian artery and occurs in under one percent of all TOS patients. That’s a good thing, since it can have the most serious complications if left untreated. It forms as a result of pressure on the subclavian artery as it passes between the scalenes and through the thoracic outlet with resulting blockages or blood clots, although an aneurysm can also occur. A larger-than-normal first rib or the presence of a cervical rib is almost associated with this particular subset of TOS. These can be seen on chest or neck x-rays. Cervical ribs are congenital in nature, and you will never know you have them unless you start experiencing symptoms or have imaging for an unrelated problem.

The symptoms for arterial TOS include pain, numbness, tingling, changes in skin color, and decreased skin temperature when compared to the other side. These symptoms almost never exist in the neck itself, as the occlusion is closer to the shoulder. Upon physical examination, the clinician may notice any one of a number of signs, including decreased pulse, possible skin color changes, and decreased blood supply to the upper extremity, including the fingers.

In severe cases, the clot or aneurysm can be palpated over the area above the clavicle. This is treated with therapy for blood clots, including anti-coagulant medications and surgery to address the osseous abnormalities and reconstruct the damaged portion of the artery. A chest x-ray is very important in these cases, because a large percentage of arterial TOS patients have the cervical rib. An ultrasound examination is also vital in order to check for the presence of a subclavian artery aneurysm or arterial stenosis. The surgical procedure will be discussed later.

A second category is the venous TOS, which is more common than arterial TOS but still accounts for only a few percent of all cases of TOS. Cases of a blood clot in the subclavian vein has also been called Paget-von Schrӧtter syndrome and are caused by several different predisposing factors, along with an acquired component. One of those predisposing factors involves narrowing of the area where the subclavian and jugular veins join to form a different vein, the innominate vein. This can be caused by the presence of a cervical rib, an enlarged first rib, or tightness of the musculature.

The symptoms of a venous TOS differ from those of an arterial TOS and can involve arm swelling, bluish discoloration, pain, numbness, or tingling. The clinician can confirm swelling through measurements, although some expected hypertrophy of the muscles resulting from pitching can be expected. Therefore, the measurements are often taken at locations where there is little additional muscle or fascia, such as at the wrist. Treatment involves a multifaceted approach, including surgery for the blood clot, removing a portion of the first rib, and sometimes performing a balloon angioplasty to address the residual narrowing of the blood vessel. Although this is primarily a clinical diagnosis, doppler ultrasound or a venography, wherein dye is injected into the blood stream and the blood flow is monitored through imaging, is also recommended. Aaron Cook and Kenny Rogers, among others, are examples of players who had venous TOS.

The third type of TOS is classified as neurogenic and accounts for 90 percent or more of the total TOS cases throughout the general population. This is further broken down into related traumatic and non-traumatic injuries. Acute hyper-extension neck injuries, such as those that occur in car accidents or falls, have been known to be associated with neurogenic TOS. Other factors include working long hours while performing repetitive motions, perhaps at a keyboard (in fact, we might feel a case coming on now).

One difference between neurogenic TOS and the other two types is that very tight scalenes are present. Symptoms of neurogenic TOS are similar to those of a “stinger” or a “burner” and can also involve compression on the brachial plexus nerve roots. Pain, numbness, tingling, and weakness in the arm and hand can be present. Neck pain is also a common complaint.

In addition to x-rays and MRIs, EMG and nerve conduction studies may be ordered to rule out other pathologies, such as carpal tunnel or cubital tunnel syndrome.

Arterial or venous TOS are treated aggressively because of the presence of a blood clot and the risk that pieces of the clot could travel to other areas of the body. Purely neurogenic TOS is treated with careful physical therapy, because certain exercises, such as neck traction and lifting heavy weights, can increase the symptoms.

If lifestyle modification and physical therapy are not successful, an injection into the scalene muscles can be beneficial for neurogenic TOS. The scalene muscles then relax, which decreases pressure on the brachial plexus by allowing the first rib to drop.

We have been hearing about more TOS surgeries in baseball players over the last few years. The common surgical procedure for all subtypes of TOS is resection of the first rib and often includes an anterior scalenectomy, in which portions of the scalene muscles are removed.

There are three common approaches: through the armpit, from the front, or from the back. The axillary approach does not allow direct repair of the arterial TOS, so the anterior supraclavicular approach is the preferred approach for this repair. The transaxillary approach is used primarily because it allows for easy visualization of all the structures with minimal damage to the surrounding muscles, as well as easy removal of the ribs. In cases of severe anterior scarring, a posterior approach can be used, but this results in significant muscle damage and a much higher risk of nerve complications.

In the transaxillary approach, the patient is under general anesthesia and is commonly given a nerve block to the brachial plexus. The patient and the arm are placed in the appropriate position and padding in order to protect the other nerves. A careful dissection is made in the armpit and carried down through the subcutaneous tissue. The surgeon then feels for the first rib as it comes around off the spine towards the clavicle. Afterwards, retractors are put in place to improve visualization in the area.

The muscle attachments are dissected from the edge of the rib. The remainder of the rib is separated from its underlying tissue, including the subclavius muscle. The scalene muscles are dissected, with special care taken to avoid the long thoracic nerve, which innervates the serratus anterior, an important scapular stabilizer. The scalene muscles are then separated from the artery and vein and dissected out, and a bone cutter is used to cut away the rib. The result is an increased area through which the neurovascular bundle can pass.

Treatment for venous TOS doesn’t always start off with the surgery described above and can often be conservative, involving anticoagulation, rest, and elevation of the arm. These measures are often not enough for athletes, baseball pitchers in particular. More aggressive treatment can involve a catheter-directed thrombolysis—removing the blood clot through a catheter—before repeating the venography to ensure the entire vessel is clear. The vein is almost always compressed at the level of costoclavicular junction.

The thoracic outlet decompression procedure described above is then performed within a week or two after the blood clot has been removed. No blood-thinning medications (such as anticoagulants) are given for the first three days, to limit the chances of a post-surgical complication. The patient is then closely followed for any redevelopment of a clot and may have repeat tests to evaluate for clots for up to six more months.

The anterior suprascapular approach is preferred among most neurosurgeons because it permits better access to the brachial plexus area, where bands of tissue connecting to the ribs can hide the nerves. In this method, the patient is again placed under general anesthesia, and a nerve block is usually administered. The patient is positioned with the proper padding to ensure that other nerves are not injured from the constant pressure. Dissection is carried down, and the external jugular vein and phrenic nerve are identified. The phrenic nerve is very important, since the two phrenic nerves—one on each side—are the only nerves to innervate the diaphragm. If the phrenic nerve is severed, half the diaphragm will be paralyzed. Breathing will still be possible, but it will be more difficult and labored.

From here, many of the same methods are used as in the transaxillary approach. The tissue is dissected off of the cervical and/or first rib before the rib(s) are carefully removed, along with the scalene muscles.



The athlete will be out for many months before beginning his throwing program and returning to the mound.

The prognosis for almost all of the injuries we have discussed in previous installments called for a good-to-excellent chance that the afflicted player would return to his previous levels. However, thoracic outlet syndrome still possesses the potential to be career-ending (or worse). Baseball was lucky to avoid such an outcome in the case of Aaron Cook and others, but it remains a possibility.