Zack Wheeler on IL with blood clot: What it means, what to expect

The Philadelphia Phillies placed Zack Wheeler on the 15-day IL on Saturday due to a blood clot in his right arm. Specifically, president of baseball operations Dave Dombrowski said Wheeler was diagnosed with a "right upper extremity blood clot," and few other details were offered. Wheeler had pitched Friday and was limited to five innings, later reporting what Phillies head athletic trainer Paul Buchheit referred to as "heaviness." Heaviness is a description patients will sometimes use when describing circulatory compromise which could occur as the result of a clot.

Blood clots in athletes may be due to a number of factors. They can occur as the result of direct trauma, resulting in bleeding or swelling that can contribute to clot formation. They can follow a period of immobilization (for instance, post-surgery when a limb is immobilized for a period of time, there can be an increased risk of clot formation). Genetic clotting disorders can be an origin source but that would be rare in an elite athlete. The most likely cause of clot formation in an elite athlete however, particularly in the upper extremity of an athlete who repeatedly subjects the arm to overhead stress, is thoracic outlet syndrome.

Thoracic outlet syndrome occurs when the first rib, or occasionally an extra rib, creates compression over the blood vessels and/or nerves as they exit the neck region under the clavicle (collarbone) and travel through the shoulder to the arm and hand. Overhead athletes -- most notably baseball pitchers along with softball players, volleyball players, rowers and swimmers -- are most susceptible to clots in the shoulder area due to thoracic outlet syndrome.

Treatment for a clot in an elite athlete depends on the root cause. According to Dr. Jason Lee, chief of vascular surgery at Stanford Health Care, who treats high performance athletes with these conditions (he is not involved in Wheeler's case), treatment can include any combination of blood thinners (for a time period ranging from one to six months) thrombolysis (a catheter-based procedure to dissolve a clot) and, in the presence of rib compression, a potential rib resection to prevent future episodes. With appropriate treatment, athletes have a very high likelihood of returning to their pre-injury level of performance.

In those cases where surgery is required, the results have been largely successful in allowing throwers to continue their careers. Examples include New York Mets ace Matt Harvey who underwent thoracic outlet surgery in 2016 and returned in 2017. Harvey struggled with other injuries but pitched until 2021, something he might not have been able to do without treatment.

In 2013, Texas Rangers president of baseball operations Chris Young, then a pitcher with the Washington Nationals, underwent thoracic outlet surgery. He signed with the Mariners the following spring and received the American League Comeback Player of the Year award after pitching 165 innings in the 2014 season.

It should be noted that both Harvey and Young underwent surgery for neurogenic thoracic outlet syndrome (the nerve compression type which is more common).