The Cardinals made official today what has been feared by Cardinals fans since spring training: Chris Carpenter will not pitch during the 2012 season.

The 2011 staff ace was diagnosed last week with Thoracic Outlet Syndrome (TOS). When the diagnosis was announced, the Cardinals also shared that the plan for Carpenter was to see if he could "pitch through it" this season before likely undergoing offseason surgery. After one bullpen session, the pitch-through-it plan has been abandoned. Carpenter has been shutdown for the season and will undergo surgical intervention.

On its informative webpage on TOS, the U.S. National Library of Medicine describes

Blood vessels and nerves coming from the spine or major blood vessels of the body pass through a narrow space near the shoulder and collarbone on their way to the arms. As they pass by or through the collarbone (clavicle) and upper ribs, they may not have enough space.

Pressure (compression) on these blood vessels or nerves can cause symptoms in the arms or hands. Problems with the nerves cause almost all cases of thoracic outlet syndrome.

The National Library Medicine webpage also describes the surgical procedure thusly:

During surgery, the following may be done:

• An extra rib is removed and certain muscles are cut.

• A section of the first rib is removed to release pressure in the area.

• Bypass surgery is done to reroute blood around the compression or remove the area that is causing the symptoms.

The prognosis for surgery to relieve TOS symptoms:

Having the first rib removed and the fibrous bands broken may relieve symptoms in certain patients. Surgery can be successful in 50% to 80% of patients. Conservative approaches using physical therapy are helpful for many patients.

At least 5% of patients have symptoms that return after surgery.