UCL Injuries: Anatomy and Risk Factors

In light of the 2022 Rays having 16 players on the IL as of the writing of this post, I wanted to create a post to discuss UCL injuries in particular. In recent years it seems the Rays have had an inordinate amount of UCL injuries and several reasons have been suggested for the root cause. I would like to help spur the conversation further and also provide some of the research that has been presented on the topic.

Anatomy and Physiology:

The ulnar collateral ligament (UCL) is found medially (pinkie finger side of the elbow joint) in the elbow and provides support against valgus force of the elbow (Starkey, 2015). The UCL can be divided into three different sections (see Figure 1): the anterior bundle (which is further divided into two more sections), the transverse bundle, and the posterior bundle (Starkey, 2015). The anterior bundle originates at the medial epicondyle of the humerus and inserts at the coronoid process of the ulna (Starkey, 2015). Further division of the anterior bundle is the anterior and posterior bands. The latter band is the tissue that primarily resists valgus forces when the elbow is flexed beyond 60 degrees (Starkey, 2015). The posterior band is primarily responsible for absorbing the valgus forces of overhead-throwing athletes (Starkey, 2015). The transverse and posterior bundles also restrain against valgus forces but will either do so ineffectively- in the case of the transverse bundle- or only after the anterior bundle has be completely disrupted (Starkey, 2015).

Further anatomical understanding of UCL injuries includes the supporting musculature that helps reduce the forces the UCL must accept or risk a higher rate of forces transferred to the UCL causing the athlete a higher risk of UCL injury. The triceps brachii, wrist flexor and pronator bundles, and the anconeus of the elbow all dynamically stabilize the elbow in an overhead-throwing athlete as the UCL on its own cannot handle the forces generated (Werner, 2002). On the other hand, the issues with limited internal shoulder rotation and excessive shoulder external rotation and poor trunk and hip strengthening along with improper throwing mechanics can place additional stress to the UCL structure and the muscles dynamically stabilizing it (Starkey 2015).

UCL Sprain Factors

When examining possible variables that increase the risk of UCL sprains research has shown correlations between different variables and the prevalence of UCL sprains. Diagnostic ultrasound was performed on minor league pitchers during spring training with the intention of finding an anatomical difference between their throwing and non-throwing elbow (Ciccotti, 2014). The throwing elbow showed an increase in UCL band thickness (mean 6.15mm) in comparison to their non-throwing arm (mean 4.56mm) (Ciccotti, 2014). While significant, this should not be unexpected. According to Davis’s Law, when soft tissue has a stress applied to it, in this situation the stress of a valgus force caused by overhead throwing, the tissue responds by strengthening itself to accommodate the forces being applied to it (Nutt, 1913). Due to this fact, an asymmetrical overhead thrower having an increased thickness of their UCL band is to be expected. The UCL is acting as the main soft-tissue restraint to the valgus force of the throw. Therefore, the body will adapt to the valgus force and increase the thickness of the UCL band in-line with Davis’ Law.

Another key factor in looking at UCL sprains is the type of pitch being thrown by the athlete and the impact it has on the valgus force being placed on the elbow. The velocity of the pitch has been shown to not have a significant correlation with elbow valgus forces despite belief that pitchers that throw at higher velocities (95mph+) would have higher forces affecting their elbow (Post, 2015). When looking at the curveball, fastball, and change-up, researcher Shouchen Dun (2008) found a difference in elbow valgus-torque for each pitch type. The fastball exhibited the greatest elbow and shoulder forces on the pitcher’s throwing arm with the change-up exhibiting the least (Dun, 2008). The pitch itself may not be the cause for elbow and shoulder pain when thrown (Dun, 2008). The number of pitches thrown, the pitcher’s mechanics, and their fatigue is more likely a factor causing UCL sprains and complications with throwing (Dun, 2008).

Research has been performed at the Major League level as well regarding pitch type and velocity in correlation to UCL injury rate. Robert Keller (2016) examined the rate of pitchers at the Major League Baseball level and their pitch velocity and pitch type breakdown in comparison to a control group to see if there is a significant correlation between any of the factors. Keller (2016) found no significant correlation between velocity and secondary pitch usage (broken down between change-up, slider, and curveballs) and rate of UCL injury. Keller did find a correlation between fastball usage and risk for UCL injury, however. Keller (2016) found for every 1% increase in fastball usage there was a correlating 2% increase in risk for UCL injury. Furthermore, a fastball usage greater than 48% was a significant predictor of UCL injury (Keller, 2016).


The UCL is critical for elbow stabilization during an overhead throwing motion. We cannot point to one single item for the explanation of UCL sprains. What we can recognize is different risk factors that increase the chance of a UCL or upper extremity injury. These are improper mechanics (due to fatigue, poor strength/mobility of the athlete, etc.), fastball usage greater than 48%, or even if they were born in a warm or cold-weather state (Erickson, 2014)! I have been lucky enough to attend several Conte Sports Medicine webinars in the past 3 years and one of the greatest pieces of information I took from it was from one of their top orthopedic surgeons: Some people are simply not built for MLB Baseball. Some people's anatomical structure is not built for the forces of pitching at the highest level of baseball.

My background in Sports Medicine

I am a certified and licensed Athletic Trainer. I am currently the head athletic trainer of a high school overseeing approximately 600-700 student-athletes. Previously, I was a graduate assistant athletic trainer for a Division I University overseeing their Men's and Women's Tennis programs along with working closely with the football and the baseball team.


1) Ciccotti, M. G., Atanda, A., Nazarian, L. N., Dodson, C. C., Holmes, L., & Cohen, S. B. (2014). Stress Sonography of the Ulnar Collateral Ligament of the Elbow in Professional Baseball Pitchers. American Journal Sports Medicine,42(3), 544-551.

2) Dun, S., Loftice, J., Fleisig, G. S., Kingsley, D., & Andrews, J. R. (2008). A Biomechanical Comparison of Youth Baseball Pitches: Is the Curveball Potentially Harmful? The American Journal of Sports Medicine, 36(4), 686–692.

3) Keller, R. A., Marshall, N. E., Guest, J. M., Okoroha, K. R., Jung, E. K., & Moutzouros, V. (2016). Major League Baseball pitch velocity and pitch type associated with risk of ulnar collateral ligament injury. Journal of shoulder and elbow surgery, 25(4), 671-675.

4) Nutt, J. J. (1913). Diseases and deformities of the foot. EB Treat & Company.

5) Post, E. G., Laudner, K. G., McLoda, T. A., Wong, R., & Meister, K. (2015). Correlation of Shoulder and Elbow Kinetics With Ball Velocity in Collegiate Baseball Pitchers. Journal of athletic training, 50(6), 629–633. doi: 10.4085/1062-6040-50.1.06

6) Starkey, C., & Brown, S. D. (2015). Examination of orthopedic & athletic injuries. Philadelphia: F.A. Davis Company.

7) Werner, S. L., Murray, T. A., Hawkins, R. J., & Gill, T. J. (2002). Relationship between throwing mechanics and elbow valgus in professional baseball pitchers. Journal of shoulder and elbow surgery, 11(2), 151-155.

This post was written by a member of the DRaysBay community and does not necessarily express the views or opinions of DRaysBay staff.