Kenny Rogers (2001). Hank Blalock (2007). John Rheinecker (2008). Matt Harrison (2009). Jarrod Saltalamacchia (2009). These are the five major leaguers from the Texas Rangers who have been diagnosed with thoracic outlet syndrome in recent history.
Aaron Cook (2004). Kip Wells (2006). Jeremy Bonderman (2008). Noah Lowry (2009). These are the four major leaguers from all other teams who have been diagnosed with thoracic outlet syndrome in recent history. [Note: There may be more, but there aren't many. This is all I could find.]
Texas Rangers 5, Everyone Else 4. The Texas Rangers also had a minor leaguer diagnosed with thoracic outlet syndrome - pitcher John Hudgins (2005).
The definition of an epidemic, according to Wikipedia, is "when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is 'expected,' based on recent experience."
Recent experience tells us that roughly 10 players have been diagnosed with TOS in the past 9 years. More than half of those players belong(ed) to a very specific population: the Texas Rangers.
Thoracic outlet syndrome (TOS) is fairly common in overhead athletes like swimmers and baseball players. The overhead movement of the arm changes the orientation of the clavicle (collar bone) in such a manner that it may compress the brachial plexus (the nerve bundle the leads into the arm from the neck) and/or the subclavian artery and vein against the first rib.
The compression usually leads to numbness or pain in the affected arm, but it can also lead to blood clots like it did with Aaron Cook in 2004.
Undiagnosed TOS can have very serious health implications. In Cook's case, a clot broke away from the compression site in his shoulder and traveled to his lungs resulting in a pulmonary embolism.
Diagnosis is clearly very important when it comes to TOS. The Texas Rangers, however, have experienced quite a large number of TOS cases in recent years. Here's a brief look at a few reasons why this may be the case.
Access to expert opinion
Dr. Gregory Pearl, of Texas Vascular Associates, is a well-respected vascular surgeon who happens to live in the Metroplex. Dr. Pearl was involved with the TOS cases for Rogers, Blalock, Harrison, and Saltalamacchia - and likely Hudgins and Rheinecker as well. This relationship history and his proximity to the ballclub makes it far easier for Texas Rangers to be diagnosed with TOS.
Kenny Rogers provided the club with a first-hand example of what TOS can do to a pitcher's performance. When Rogers returned with an extra 4-5 mph on his fastball, Dr. Pearl was probably put on speed dial.
Throwing mechanics
Pitchers are a high risk group for TOS compared to position players because of the quantity and intensity of their throws but also because of the way they turn their heads toward the plate. With the previous image in mind, take a look at Matt Harrison.
When the head and neck turn away from the compression site, the brachial plexus and subclavian blood vessels are pulled into the narrowing gap between the rib and clavicle.
For low intensity throws where the head doesn't turn, TOS is less of a concern.
Training methods
Of particular note are position players Hank Blalock and Jarrod Saltamacchia, each of whom had TOS in his throwing shoulder. To discount their mechanics entirely would be foolish, but I found no reports of TOS diagnosis in any other position player. This suggests, perhaps incorrectly, that something behind the scenes has made a significant contribution.
Weight lifting can produce stress far in excess of what an intense throw can produce, but it's practically impossible to properly perform any exercise and cause thoracic outlet compression at the same time. When bad form enters the equation, though, all bets are off.
Dynamic exercises may contribute an intertial element in a manner similar to that of throwing a baseball. Even these, when performed properly, aren't likely to be significant contributors. As with weight lifting, if they are not performed correctly, they become a risk for TOS and a number of other potential problems.
If training is to blame, it's likely a series of exercises rather than a single one that results in thoracic outlet compression.
Blind, stinking luck
Not to be overlooked is random chance. It is entirely possible that the Texas Rangers have simply been unlucky. It is possible that each affected player was genetically at risk for TOS and would have been diagnosed no matter what team he was playing for. It may be nothing more than luck that has brought these players to Arlington.
So which is it?
In truth, it's most likely a combination of these factors. Given the current state of exercise science, training methods are probably the least likely to blame.
Throwing mechanics and luck combined with having a "resident" expert have likely been equally responsible for the Rangers' having lapped the rest of Major Leage baseball in thoracic outlet syndrome diagnoses.
[Historical TOS Note: David Cone and J.R. Richard, both pitchers, were also known/beleived to have suffered from thoracic outlet syndrome, but both diagnoses were well before the "Dr. Pearl era."]