Colby Lewis, Texas Rangers reliable right-handed starting pitcher, will undergo surgery this week to repair a flexor tendon at his right elbow. He reportedly had an MRI that revealed the small tear prior to going on the DL on June 24, but determined only after his return to the mound on July 18 that surgery would be his best bet. Lewis pitched successfully for five innings in this recent outing, allowing one run and three hits, but reported having tightness over the last two innings before leaving the game.
The Flexor Tendons
There are a total of nine muscles located in the palm side of the forearm. Some play a role in flexing the wrist or fingers, while others rotate (pronate or supinate) the forearm. Some of these also assist with bending the elbow. These muscles are divided into three layers and the five in the outermost (superficial) and middle layers all attach at the inner elbow in what is known as a common flexor tendon.
Two of these muscles -- Flexor Carpi Ulnaris (FCU) and Flexor Digitorum Superficialis (FDS) -- overlap the ulnar (medial) collateral ligament of the elbow (UCL). This is the ligament that often tears in throwing athletes, requiring Tommy John surgery. The FCU is especially positioned over the ligament when the elbow is flexed at a right angle. Due to their location and function, these muscles are considered to assist with the dynamic stabilization of the inner elbow.
Ulnar collateral ligament injuries occur in throwing athletes because of the extreme and repetitive loading on the medial (inner) elbow during the pitching motion. This valgus stress is greatest just after the cocking phase. The acceleration phase of pitching also results in a good deal of valgus stress. Muscular activity of the FCU and FDS is also heightened during acceleration. One can see why these flexors are so intimately involved and at risk.
As an aside, in the presence of a UCL injury, the activity of the FCU and FDS, as well as that of another of the flexors (Flexor Carpi Radialis -- FCR) drops significantly. Yet another reason, along with laxity (instability) of the inner elbow, for a pitcher to be incapacitated by UCL involvement.
A flexor tear may not be out of the ordinary, but unfortunately for Colby Lewis, it could be up to a year before he is fully back in action.
(Additional sources: Davidson: AJSM '96, Hamilton: JSES '96)