Baseball & it’s classic injury known as the “Tommy John”
With the 2016 baseball in full ‘swing’, it is worth discussing elbow injuries. The classic injury that comes to mind first is the one that requires ulnar collateral ligament (UCL) reconstruction, or more commonly known as “Tommy John” surgery.
The ulnar collateral ligament is an important structure for medial elbow stability. Its fibres are aligned to reinforce the medial elbow (or inner elbow). There are two groups of fibres the UCL; the anterior (front) and posterior (back) fibres. Together, these fibres will resist ‘valgus’ force to the elbow; a valgus force will rotate the forearm outwards relative to the humerus, creating an angle at the elbow where the hand is pointing away from the body. As with any other tissue in the body, if these fibres are stretched beyond their limits, they will become injured. The degree of the injury is dependent on the amount that the tissue is stretched.
Imagine the throwing motion starting from the legs to generate power and transferring to the trunk and core, multiplying through the throwing arm and releasing at the hand to propel the ball in a ‘whip-like’ kinetic chain. Through this pathway, the body needs to resist the amount of force that is being generated. The smallest structures would be in the arm, but it also has the highest demands to resist force without failing (given the multiplication of force down the kinetic chain). Throwing a baseball imparts a significant valgus stress on the elbow, directly applying strain on the UCL. As pitchers try to throw the baseball at higher velocity, the force that is generated is increased, placing the UCL at higher risk for injury.
But, not every pitcher experiences elbow pain or will sustain an injury. So, there must be more at play that determines injury and elbow stability. 
Forearm muscle strength is a critical component in determining elbow injury and pain. There are two muscles in the forearm that were found to be critical in elbow stability; these are the flexor carpi radialis and the flexor digitorum superficialis; both muscles contribute to flexing the wrist. In cadaver studies, the fibres of these muscles were found to cross at the elbow in parallel with the anterior fibres of the UCL, and therefore enhanced the function of the UCL. This means that with increased strength of these muscles, the athlete will be able to produce more force to generate ball velocity, but will also be able to actively resist the amount of valgus force at the elbow. These muscles will contract, providing an opposing and resistive (varus) force to the valgus defmoration that occurs at the elbow during a throw. In fact, the function of these muscles can be so profound that some pitchers (albeit one well-known pitcher is a knuckleballer) can pitch without a UCL on their throwing arm and still perform at a high level.
Of course, in determining injury, there are many other factors that are major contributors including pitch type, pitching mechanics, throwing arm angle, previous injury, elbow flexion contracture, and glenohumeral internal rotation deficit. But this is understandable because throwing is a motor skill that is quite complex and requires considerable practice to master. Be sure that you are ready for this season by training appropriately.
By: Chris Dahiroc, PT, M.Sc., P.T.
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