risk factors for ucl injury cover

Risk Factors for UCL Injury in Athletes

The ulnar collateral ligament bundle is made up the anterior, posterior, and transverse bands. The anterior band is most frequently injured in throwing. The anterior band originates from the medial epicondyle and inserts on the sublime tubercle of the ulna (3). The anterior band acts to oppose the high valgus stress put on the elbow during the acceleration phase of throwing (1). A cadaver UCL can withstand 32.1 N-m of valgus stress before failing (10). In a study published in the American Journal of Sports Medicine by Glenn Fleisig and James Andrews, they found that the UCL was subjected to 34.6 N-m during pitching, which puts it right at the point of failing (10).
As pitchers continue to throw harder and faster, the incidence of UCL injuries has been increasing. To date, there still has not been a rehab program that has been shown to prevent the development of UCL tears. As a result, we have shifted to identifying risk factors for injury and using these to modify activity in those individuals at risk. Studies looking in to UCL injuries most commonly focus on pitch volume, pitch type, and biomechanics of pitching.
Published in the American Journal of Sports Medicine in 2006, researchers looked at risk factors for developing a UCL injury. What they found was that pitchers who threw more than 100 innings in a year had a 3.5 times higher risk of developing a serious injury (4). This builds on previous studies that show an association with pitch count in a season and developing elbow pain (5). Based on some of this early data regarding innings pitched and pitch count, the USA Baseball Medica/Safety Advisory Committee put out their recommendations on pitching and rest. Figure one is a table that was endorsed by the USA Baseball Medical/Safety Advisory Committee on days of rest for pitchers (6).
pitching program for little league elbow table

Table 1: Pitching program for return to play for athletes

Researchers have also looked into if there is an increased risk for elbow injuries with curveballs. The pervading wisdom is that throwing curveballs puts higher stress on a pitcher’s elbow. Published in 2002 out of the American Sports Medicine Institute, researchers looked at the effect of pitch type on youth baseball pitchers. They evaluated a group of little league pitchers throughout the season to see if they could identify risk factors for shoulder or elbow injury (5). They used multiple modalities including biomechanical pitching evaluation and post pitching questionnaires (5). What they found was that throwing breaking balls and having a high pitch count were found to have increased risk of elbow and shoulder pain (5).
However, Dr. Andrews reviewed the follow up studies to this initial study and they found that pitch type was not found to increase the risk for elbow or shoulder surgery (4). They again identified that the overall volume of throwing increased the risk for developing elbow or shoulder injury (4). A survey of both nonprofessional and MLB pitchers asked them to identify what they thought were risk factors for UCL injury. Over 40% of pitchers thought that throwing more curveballs led to UCL injuries (13). However, in 2009 a group of researchers looked at the amount of elbow torque in little league pitchers between fastballs, changeups, and curveballs. They found that fastballs had the highest elbow varus torque followed by curve-balls (15).
Researchers have also looked at pitch velocity as a risk factor for UCL injury. In a study published in the American Journal of Sports Medicine in 2016, Dr. Chalmers looked at MLB pitchers’ velocities and their incidence of UCL injury. They looked back on a group of MLB players who had undergone ULC reconstruction and looked at their pre-injury pitch velocity. They found that 20% of pitchers who threw over 95.7MPH required UCL reconstruction (7). This is in contrast to only 7% of pitchers whose peak velocity average was under 86.9 MPH (7). The same study also identified BMI as a risk factor for UCL reconstruction. They found that the percentage of pitchers requiring UCL reconstruction went up with a higher BMI (7).
Another study published in the American Journal of Sports Medicine by David Whiteside also looked for risk factors of UCL reconstruction in Major League Baseball Pitchers. They found that less time between starts or relief appearances was associated with an increased risk of UCL reconstruction (8). They also found that throwing more pitch types decreased the risk of UCL reconstruction (8). This study also confirmed that pitch velocity is a risk factor of UCL injury (8).
ucl ulnar collateral ligament anatomy

Image 2. Illustration of ulnar collateral ligament (courtesy of upswinghealth.com)

Studies have also looked into pitching biomechanics to identify risk factors for UCL injury. One study looked at nondominant arm humeral torsion as a risk factor for UCL injury. Researchers found that an increased humeral retrotrosion angle was associated with UCL injury (9).
It is also well known in the literature that loss of glenohumeral internal rotation is a risk factor for shoulder and elbow injury. In a study published in the Journal of Elbow and Shoulder Surgery, they found that pitchers with UCL injury had greater loss of glenohumeral internal rotation than pitchers without UCL injury (11). Researchers also found that having a more lateral pitch release angle increased risk of UCL injury (14).
There has been an increase in the number of UCL reconstructions which has led to many studies looking at what we can do to decrease this number. Studies are all in agreement that number of innings and pitch count are two easily modified risk factors. There has also been a trend in studying the biomechanics of throwing to identify risk factors for UCL injury. Despite all we have learned regarding changes in pitching mechanics to cut down UCL injuries, we have not figured out a way to decrease the valgus torque applied to the UCL ligament. For now, we need to continue monitoring our pitchers’ volumes and correcting mechanical abnormalities.
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5) Lyman, Stephen, et al. “Effect of Pitch Type, Pitch Count, and Pitching Mechanics on Risk of Elbow and Shoulder Pain in Youth Baseball Pitchers.” The American Journal of Sports Medicine, vol. 30, no. 4, Aug. 2002, pp. 463–68. PubMed, doi:10.1177/03635465020300040201.

6) Kerut EK, Kerut DG, Fleisig GS, Andrews JR: Prevention of arm injury in youth baseball pitchers. J La State Med Soc 2008;160(2):95-98
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9) Meyer, Casey J., et al. “Baseball Players With an Ulnar Collateral Ligament Tear Display Increased Nondominant Arm Humeral Torsion Compared With Healthy Baseball Players.” The American Journal of Sports Medicine, vol. 45, no. 1, Jan. 2017, pp. 144–49. PubMed, doi:10.1177/0363546516664718.
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11) Ostrander, Roger, et al. “Glenohumeral Rotation Deficits in High School, College, and Professional Baseball Pitchers with and without a Medial Ulnar Collateral Ligament Injury.” Journal of Shoulder and Elbow Surgery, vol. 28, no. 3, Mar. 2019, pp. 423–29. PubMed, doi:10.1016/j.jse.2018.11.038.
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