Zack Wheeler: What is thoracic outlet syndrome? Here’s all to know

The Philadelphia Phillies have been dealt a major setback as star pitcher Zack Wheeler has been ruled out for the remainder of the 2025 season. The 35-year-old ace underwent surgery this week after being diagnosed with venous thoracic outlet syndrome, a rare condition that causes blood clots by compressing veins in the shoulder area. Doctors performed a procedure to remove the clot from his throwing arm, and while his recovery will sideline him for six to eight months, there is optimism he could be ready by Opening Day 2026.

Venous thoracic outlet syndrome is a serious but treatable condition, often managed through surgery that involves the removal of a rib to ease pressure in the affected area. The Phillies confirmed that Wheeler’s operation was successful, but the road to recovery will require careful monitoring and rehabilitation.

Manager Rob Thomson acknowledged the severity of the situation, stressing that while Wheeler’s absence hurts the team’s immediate playoff ambitions, his health comes first. “It’s unfortunate, but we’re just grateful he’s safe and on the path to recovery,” Thomson said.

Since joining the Phillies in 2020, Wheeler has established himself as one of the most dominant pitchers in the game. Known for his durability, pinpoint command, and overpowering arsenal, he has consistently ranked among the league’s best, regularly contending in Cy Young discussions. This season, he had been in peak form, striking out a league-leading 195 batters in just under 150 innings with an impressive 2.71 ERA.

His absence will undoubtedly test the Phillies’ depth, but the team still boasts a strong rotation led by Aaron Nola, Ranger Suárez, Cristopher Sánchez, Jesús Luzardo, and Taijuan Walker. In addition, top prospect Andrew Painter could emerge as a reinforcement down the stretch. Team president Dave Dombrowski emphasized that while Wheeler’s presence can’t truly be replaced, the Phillies remain confident in their pitching depth and overall roster strength.

As of now, Philadelphia holds a six-game cushion at the top of the NL East, keeping them in prime position for a playoff push. Still, losing their ace at such a crucial stage of the season represents a heavy blow to their championship aspirations. For Wheeler, however, the focus is firmly on recovery and ensuring he returns to full strength for 2026.

Understanding Thoracic Outlet Syndrome (TOS)

Thoracic Outlet Syndrome (TOS) is a medical condition that occurs when blood vessels or nerves in the space between the collarbone and the first rib — an area known as the thoracic outlet — become compressed. This compression can lead to pain, tingling, numbness, and weakness in the shoulders, arms, and hands. In some cases, it can also cause circulation problems due to restricted blood flow.

Types of TOS

There are three main forms of Thoracic Outlet Syndrome, classified by the structures that are affected:

1. Neurogenic TOS – The most common type, involving compression of the brachial plexus (a network of nerves that control muscle movement and sensation in the shoulder, arm, and hand).

2. Venous TOS – A rarer form caused by compression of a vein, often leading to swelling, pain, and blood clot formation in the arm.

3. Arterial TOS – The least common but potentially the most serious, involving compression of an artery, which can lead to serious circulation issues.

Causes and Risk Factors

Thoracic Outlet Syndrome can develop for several reasons. Some people are born with anatomical abnormalities, such as an extra rib or unusual muscle structure, which predispose them to compression. Others develop it due to repetitive activities (such as pitching in baseball, swimming, or weightlifting), traumatic injuries (like whiplash from a car accident), or poor posture that places constant pressure on the outlet area.

Symptoms

The symptoms vary depending on the type:

• Neurogenic TOS: Tingling, numbness, and weakness in the arm or hand.

• Venous TOS: Swelling, heaviness, and bluish discoloration of the arm; possible blood clot.

• Arterial TOS: Cold sensitivity, pain in the hand, and poor circulation that may lead to ulcers or tissue damage if untreated.

  
  
  

Diagnosis

Because symptoms often mimic other conditions such as carpal tunnel syndrome or cervical spine disorders, TOS can be difficult to diagnose. Physicians usually rely on a combination of physical exams, imaging tests (X-rays, MRI, or CT scans), ultrasound, and nerve conduction studies to pinpoint the cause of compression.

Treatment Options

Treatment depends on the severity of the condition:

• Non-surgical approaches: Physical therapy is often the first line of treatment, helping patients strengthen shoulder muscles, improve posture, and relieve pressure. Pain management, lifestyle modifications, and medications such as blood thinners (for venous TOS) may also be prescribed.

• Surgical treatment: In severe cases, surgery may be required to remove a rib, repair blood vessels, or release compressed nerves. Athletes like pitchers sometimes undergo surgery when clots or circulation issues threaten their careers.

Prognosis and Outlook

With early diagnosis and proper management, most people with Thoracic Outlet Syndrome improve significantly. Athletes often face long recovery times but can return to their sport if rehabilitation is successful. Untreated cases, however, especially those involving blood clots or arterial compression, can lead to serious complications.