Relationship between the medial elbow adduction moment during pitching and ulnar collateral ligament appearance during magnetic resonance imaging evaluation.

BACKGROUND Medial elbow distraction during pitching as the primary mechanism contributing to adaptations in ulnar collateral ligament (UCL) appearance during magnetic resonance imaging (MRI) evaluation has not been established. HYPOTHESIS Uninjured high school-aged pitchers with unilateral adaptations of the UCL exhibit a higher peak internal elbow adduction moment than those without UCL adaptations. STUDY DESIGN Cohort study (Prevalence); Level of evidence, 2. METHODS Twenty uninjured, asymptomatic high school-aged pitchers underwent bilateral elbow MRI examinations. Three-dimensional motion analysis testing was performed to collect throwing arm biomechanics as participants pitched from an indoor mound. Nonparametric tests were performed to compare peak internal elbow adduction moment in uninjured participants with and without adaptations in UCL appearance and to determine the nature of the relationship between the peak internal adduction moment and UCL appearance. RESULTS Uninjured participants with UCL thickening exhibited a higher peak internal elbow adduction moment of 53.3 ± 6.8 N·m compared with uninjured participants without adaptations in UCL appearance, 38.8 ± 10.9 N·m (P = .05), as higher moments were correlated with ligament thickening (correlation coefficient, 0.45) (P = .02). CONCLUSION This study establishes the association between medial elbow distraction captured by the internal adduction moment during pitching and UCL adaptations visible during MRI evaluation.