February 6, 2013

Collateral Damage

Barely Begun and Already Through

by Corey Dawkins and Stephani Bee

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Chris Carpenter made an amazing return from Thoracic Outlet Syndrome (TOS) surgery last year, but his 2013 season—and, potentially, his career—is now in jeopardy following a setback with his shoulder. Carpenter was throwing off the mound recently when his symptoms returned, this time worse than before. He is also experiencing numbness in his arm and bruising in his shoulder and hand. Carpenter informed Cardinals general manager John Mozeliak of the situation after trying to throw three different times without success. During their conversations, Carpenter expressed concern about how his shoulder will respond to life after baseball, let alone pitching at a high level.

Carpenter’s surgery was not an experimental one, but it’s not a common one, either. The area affected involves the neurovascular bundle as it passes from the neck and trunk through the shoulder and down the arm, as pictured in Figure 1.

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Figure 1 Thoracic Outlet

TOS has a wide range of causes, including extra muscles in the neck, scar tissue in the area, an extra cervical rib, hypertrophy of normal musculature, tight scalene or pec minor muscles, or trauma such as car accidents. Microinstability in the shoulder might also play a role. Regardless of cause, the results can include decreased blood flow or nerve function, or both. You can see an example of decreased blood flow in an arteriogram (a special diagnostic test to look specifically at blood flow) of a collegiate baseball pitcher with TOS caused by pec minor tightness in Figure 2. The thin arrow represents the axillary artery being compressed by the tip of the corocoid process (thick arrow).

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Figure 2 Arteriogram of TOS

Carpenter underwent surgery last July to remove a portion of a rib along with some muscles that attach near the neurovascular bundle, which is explained in Figure 3.

Most pitchers with this condition take the better part of a year to return to pitching at the major-league level, if at all, but Carpenter managed to return after only a few months. However, it was clear Carpenter wasn’t anywhere near his best. His velocity and control suffered, and we recently found out he had discomfort in his last start of the year. There was still optimism that the offseason would allow Carpenter to fully recover and slowly build up his strength again. Everything looked to be heading that way until he ramped up his training regimen.

Carpenter will undergo further tests and an examination by Dr. Gregory Pearl, the surgeon who performed Carpenter’s surgery last year, to find the cause of his trouble. The most likely culprit at this point is the pressure caused by the pec minor muscle, but sometimes the cause is never fully found. 

Corey Dawkins is an author of Baseball Prospectus. Follow @CoreyDawkinsBP
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Stephani Bee is an author of Baseball Prospectus. 
Click here to see Stephani's other articles. You can contact Stephani by clicking here