When a blood clot was found near Zack Wheeler‘s right shoulder, there was no talk of when he might return to the Phillies rotation because the diagnosis held potentially life threatening implications. The fear with a blood clot anywhere in the body is that it can break loose and move anywhere in the body, including the heart or brain, which can lead to death.

Surgery to remove the blood clot was successful so Wheeler is out of that danger. Now, the focus could return to baseball and the news was not good. Surgeons discovered that the Phillies ace has venous thoracic outlet syndrome (TOS), a condition that compresses and damages a nerve or nerves in the shoulder. It’s that condition that caused the development of the blood clot.. Wheeler will undergo surgery to repair the condition and miss six to eight months.

There are two types of TOS. The more common one is neurogenic thoracic outlet syndrome while the less common and more severe type is venous thoracic outlet syndrome. As the names imply, neurogenic TOS is when a nerve or nerves are pinched and causes swelling and causes pain, numbness, and weakness in the arm. venous TOS is when a vein is compressed which does not allow for sufficient blood flow in the arm and causes swelling, discoloration, and heaviness in the arm.

While every recovery from an injury is different, a good comparison to Wheeler is Rangers pitcher Merrill Kelly who underwent surgery to repair venous TOS in August of 2020 when he was with Arizona. Kelly came back in 2021 and made 27 starts with a 4.44 ERA, directly in line with his 4.42 ERA from 2019 his last full season prior to the surgery. The following season Kelly threw 200.1 innings in 33 starts with a 3.37 ERA. As for age, Kelly was two months shy of 32-years-old while Wheeler just turned 35 in May.

With the return of Aaron Nola from the IL just as Wheeler went on the IL the Phillies have a full five-man rotation with Nola, Jesus Luzardo, Ranger Suarez, Taijuan Walker, and likely Cy Young candidate Cristopher Sanchez.