Paper 22: The Natural History of Ulnar Collateral Ligament Injuries in Professional Baseball
Authors: Tanenbaum Joseph , Hartwell Matthew , Tenner Zachary , Selley Ryan , Buchler Lucas , Saltzman Matthew , Gryzlo Stephen 
Published: August 2024

Objectives: The objective of this study was to quantify the rate and timing of recurrent ulnar collateral ligament (UCL) injuries among elite baseball players. Whereas several prior works focused on rates of return to play and performance after UCL reconstruction, the literature lacks evidence on recurrence rates for UCL injuries, especially for non-operative injuries. Addressing this literature gap is important because of the emphasis that team physicians place on UCL injury history as a determinant of future UCL injury risk. In a landmark study that surveyed Major League Baseball (MLB) team physicians and achieved an 80% response rate, McGahan et al. found that 60% of team physicians rated any prior UCL injury (regardless of injury severity or treatment modality) as “moderate risk” for future injury among pitchers entering the MLB draft. In the same survey, 52% of team physicians rated recent UCL strain as a “severe risk” for future injury among the same player cohort. The present study is the first to use comprehensive data from MLB on UCL injuries to quantify the frequency of recurrence and when these injuries are likely to recur. Quantifying the recurrence rate of UCL injuries is important for players at all levels of competition, including those without a documented injury history. For example, one single-center study found that 34% of asymptomatic MLB and Minor League Baseball (MiLB) players screened with a pre-signing MRI had evidence of UCL signal heterogeneity. Alternatively, if the recurrence rate of UCL injuries is relatively low, then players and teams may be inappropriately weighting prior injury as a predictor of future injury risk. This study builds on the work of McGahan et al. by quantifying the recurrence rate of UCL injuries in professional baseball players and defines the typical number of seasons until recurrence. These data will provide critical information to players, team management, and team physicians at all levels of competition with an eye toward better informing health and safety decisions. Methods: This study uses data supplied by Major League Baseball’s Health and Injury Tracking System (HITS) on all MLB and MiLB players from 2010-2021. A comprehensive list of UCL injuries (regardless of severity or initial treatment modality) was generated by reviewing every elbow injury in MLB and MiLB during the study period. Use of this data source marks an important departure from prior studies on similar topics that relied on public injury reports to determine if a player had a UCL injury. Instead, these data are generated by the athletic trainers, team surgeons, and league office and are therefore more comprehensive than earlier studies of similar questions. Within HITS, each player is given a unique player identifier and each injury event is given a unique injury event identifier. Thus, if a player is injured in two separate seasons, the player ID would be present in both years but the event ID would be different. This differentiation allows player tracking over time and to determine when an injury recurs. We calculated the number of UCL injuries in each season of 2010-2016 and then determined the five-year recurrence rate. We chose the five-year time point because the median professional baseball career length is 5 seasons. We therefore present data on the five-year recurrence rate for the 2010-2016 seasons, but rely on data from throughout the study period (2010-2021) to determine those rates. We subsequently determined the median and interquartile range for when a recurrence was most likely to occur. Next, we calculated the five recurrence rate among players whose initial injury was managed non-peratively. Finally, we quantified the rate at which recurrent injuries were managed operatively stratified by initial treatment modality. Results: Throughout the study period (2010-2016), there were 1,766 documented UCL injuries. Of these injuries, 820 (46%) were managed initially with surgery, 177 (10.0%) recurred within five years, with a median of two seasons (Interquartile range [IQR] 1-3 seasons) until recurrence. When a recurrence occurred, 107 players (60.5%) underwent surgery, regardless of initial treatment modality. Among injuries that were initially treated non-operatively (946 injuries), 126 players (13.3%) experienced a recurrence within five years, with a median of two seasons (IQR 1-3 seasons) until recurrence, and 87 players (69.0%) underwent surgery to treat the recurrence. Conclusions: The present study offers the most comprehensive data to date on the natural history of UCL injuries among elite baseball players. As McGahan et al. showed, many team physicians use a history of UCL injury as an indicator of future UCL injury risk. It is therefore important to identify the risk of injury recurrence during the typical professional baseball career. We found a relatively low recurrence rate of 10% within the median professional baseball career length of five years. Even players who were initially treated non-operatively (identified by McGahan et al. as being perceived to be more likely to sustain a future UCL injury) had a relatively low five-year recurrence rate of 13.3%. Importantly, the majority of recurrences underwent surgery, suggesting that the risk tolerance for future recurrences beyond the first recurrence is similarly low. These results highlight the importance of understanding the natural history of common injuries among athletes across all levels of competition, and can be used to inform risk reduction plans for athletes across the competitive landscape.