Objective: This study aimed to investigate whether flexor digitorum superficialis (FDS) dysfunction could serve as a risk factor of throwing elbow injuries.
Design: This prospective cohort study recruited 31 male college baseball pitchers from June 2022 to May 2023.
Setting: A set of college baseball pitchers of male sex participated in this study and measurements were taken before and after pitching 30 and 50 pitches.
Participants: This study included 31 male college baseball pitchers.
Assessment of risk factors: Using ultrasonography, the presence of an intra-articular ring-down artifact (RDA) was assessed with 4 different conditions: at rest, under gravity valgus load, and under elbow gravity valgus stress with either the contraction of the third and fourth digits or of the second and fifth digits.
Main outcome measures: Each participant threw 50 fastballs at a distance of 18.44 m from the pitcher's plate toward a catcher. These measurements were taken before pitching and after 30 and 50 pitches, and all elbow injuries during the study period resulting in medical evaluation or missed participation were considered as the primary outcome.
Results: Nine pitchers (29%) experienced throwing elbow injuries. Cox regression analysis indicated that the presence of the RDA under valgus stress with FDS contraction involving the second and fifth digits was a significant risk factor for throwing elbow injury (hazard ratio: 5.4; P = 0.018).
Conclusions: Dysfunction in the deep layer of the FDS may serve as a risk factor of throwing elbow injury in college baseball pitchers after throwing 50 pitches.
Level of evidence: Diagnostic, level 2.
Keywords: college baseball player; dynamic stabilizer; elbow; flexor digitorum superficialis; risk factor; sonography; ulnar collateral ligament injuries.
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