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Very early into the 2024 season, pitcher injuries have become a highly talked about issue. Big name pitchers like Shane Bieber, Spencer Strider, Eury Pérez, Jonathan Loáisiga, Robert Stephenson, and others have all gone down with elbow injuries this year alone. As velocity, spin, and movement continues to increase, so do pitcher injury rates. Each of these factors and others are leading to all-time highs in the stress placed on pitcher’s arms, partially contributing to the UCL injuries that require Tommy John. Players have also named other reasons they feel are contributing to more injuries, including the pitch clock, which was specifically named in an MLBPA statement. MLB responded with a statement of their own, and despite their stated commitment to decreasing pitcher injuries, and claimed that this assertion is unfounded and not backed up by data and research. Pitchers have also posited that recent enforcements of the foreign substance ban has forced them to change grips and mechanics, causing additional strain and injuries.

Today, let’s examine the Tommy John data to see the recent trends among pitchers across time and levels, as well as the contribution of different variables to injury.

Shoutout to Jon Roegele (@MLBPlayerAnalys on X), his work to maintain the Tommy John Surgery List is what enables this project, go give him a follow if you aren’t already.

Elbow Injury Trends

Since 2015, Tommy John surgeries have generally risen year to year. They were at their lowest in the Statcast era in 2016 and 2019, when 19 MLB pitchers got the procedure in each season. This number peaked in 2021, when 35 big leaguers required the surgery. This was likely contributed to because of workload management issues following COVID shutdowns and the shortened season in 2020. Through four months in 2024, 11 pitchers at the MLB level have been operated on, a number that doesn’t even include Wade Miley scheduled surgery for May 1st. At this pace, 33 surgeries will be performed, which would be the 2nd highest mark of the Statcast era. March and April have been especially rough this year, as each are tied for the 2nd highest number of surgeries for that month since 2015.

On a team basis, more Mets pitchers have gotten Tommy John since 2015 than any other club, especially their minor leaguers. On the other hand, just 11 surgeries have been performed on Diamondbacks pitchers at all levels, the same amount as Mets pitchers at the MLB level alone. Advanced player and pitching development organizations like the Yankees, Brewers, and Guardians, are all near the top of list as well, indicating that there could be a potential link between the pitch quality/velocity programs that these teams employ to maximize pitcher stuff.

Pitchers can also get a UCL repair with an internal brace to help reconstruct damage to the UCL. This was the procedure of choice for Strider, Giolito, and others. At its current pace, this surgery will be performed 9 times, far greater than the previous high of 5 in 2021 and 2023, which included position players.

It will be interesting to see if this procedure continues to gain popularity as an alternative to Tommy John, as it generally has a shorter recovery time.

What Variables/Factors Affect Injury?

As mentioned earlier, improvements in league-wide pitch quality have coincided with the increase in elbow injuries. Many have debated the role that factors like pitch type selection and frequency, velocity, and shape have in increasing injury risk. Additional considerations that don’t often get discussed as often are changes in mechanics whether that be due to a different arm slot of change in release due to the addition of a new pitch. Anecdotally, many pitchers have embraced a sweeper recently because of its relative ease to pick up and effectiveness against same-handed hitters, but this pitch requires supination that could potentially cause strain for pitchers who naturally tend to pronate more easily. With the help of machine learning, we can attempt to quantify this. I trained an XGBoost machine learning model that predicts whether a pitcher will require Tommy John surgery with features like Fastball%, Breaking Ball spin, whether they added a new pitch and others. XGBoost provides metrics to describe the importance of a feature in making predictions, which gives us an idea of which key indicators to monitor. Here is the most important variables, in plot form:

Breaking ball spin shows up as the most important feature for predicting whether a pitcher got Tommy John surgery or not. This makes sense, as extreme manipulation of of a pitch’s spin while throwing at or near max effort would put a lot of strain on an elbow. Interestingly, a pitcher’s extension is the next most important feature. The amount of pitches thrown is also important, because higher volume means more stress on an arm. Release point is also meaningful, as well as the velocities a pitcher throws each of their pitch types as, which is intuitive. Release point changes can also hold information relevant to an injury risk.

Hopefully, going forward, teams will make progress in their understanding of biomechanics and find ways to reduce elbow strain while maintaining pitch velocity and quality. It is in MLB’s best interests to find a way to keep their big names on the field as much as possible, yet it seems as though injuries will continue to increase for the foreseeable future as velocity does as well.

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