Poster 204. Using Pitch-Tracking Metrics to Identify Warning Signs Immediately Prior to Acute Ulnar Collateral Ligament Injuries in Major League Baseball Players

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Objective: While ulnar collateral ligament (UCL) injuries have been widely studied, no investigations have characterized the kinematics of acutely presenting UCL injuries or examined the pitch-by-pitch sequence leading up to ligament failure. Therefore, the primary objective of this study was to evaluate if acute UCL failure is preceded by detectable changes in pitch-tracking metrics such as velocity, spin rate (rpm), release extension (feet), arm angle (degrees), and acceleration, or if it occurs without biomechanical warning. The clinical implications of this are significant-identifying real-time deviations that precede injury may allow teams to develop rest or treatment protocols that can help prevent UCL injuries, or decrease the severity of injury, with certain tear patterns being more amenable to UCL repair and the shorter recovery timeline than more severe full thickness tears. Methods: Seven MLB pitchers who sustained acute UCL injuries on a single pitch between 2020 and 2025 were retrospectively identified. Statcast data from the injury game and four prior outings were analyzed for each player. Five pitch-tracking metrics (velocity, spin rate, release extension, arm angle, and acceleration magnitude) were extracted for each pitch. For each pitcher and pitch type, a principal component model was trained on control outings; Mahalanobis distance (MD) was calculated to quantify multivariate deviation from baseline. To assess short-term variability, MD values from the five fastballs before injury were summed and compared to control-derived thresholds. Pitch-to-pitch trends in MD and individual features were analyzed for progressive changes. Matched controls were selected according to age, handedness, starting vs relieving pitcher, and season pitch count. The same process was then completed for a five game sample window of pitches for these matched controls. Results: Principal component analysis and MD analysis revealed three principal findings: (1) every injury pitch was a mechanical outlier based on MD exceeding the 95 th percentile of the control distribution, (2) suppressed velocity and reduced arm angle consistently marked the injury pitch, and (3) 86% of pitchers showed elevated cumulative mechanical deviation across the five fastballs preceding injury. This was in contrast to matched controls, who had no variation in final pitches and only 7% showed elevated cumulative mechanical devation across the five preceding fastballs. Conclusions: This exploratory study provides the first biomechanical characterization of acute UCL failure at the pitch-by-pitch level. Analysis of over 300 pitches between seven Major League Baseball pitchers who sustained sudden UCL ruptures requiring surgical intervention revealed three principal findings: (1) every injury pitch was a mechanical outlier based on MD exceeding the 95ᵗʰ percentile of the control distribution (2) 86% of pitchers showed elevated cumulative mechanical deviation across the five fastballs preceding injury, and (3) suppressed velocity and reduced arm angle consistently marked the injury pitch. This was in contrast to matched controls, who had no variation in final pitches and only 7% showed elevated cumulative mechanical deviation across the five preceding fastballs. Collectively, these findings suggest that acute UCL failure represents a distinct biomechanical phenotype characterized by abrupt decompensation during the injury game, rather than a gradual decline over multiple prior outings.

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