Clinical Utility of the Japanese Version of the Kerlan-Jobe Orthopaedic Clinic Shoulder and Elbow Score for Detecting Upper Extremity Dysfunction in High-School Baseball Players.

Background: Upper extremity injuries are prevalent among high school baseball players, many of whom continue playing despite mild or early symptoms. Although the Kerlan-Jobe Orthopaedic Clinic Shoulder and Elbow Score (KJOC) is a validated patient-reported outcome (PRO) for overhead athletes, its sensitivity in identifying early dysfunction in field-active adolescent athletes remains unclear. Hypothesis/Purpose: This study aimed to determine the clinical utility of the Japanese version of the KJOC (J-KJOC) for identifying symptomatic high school baseball players and to establish a cutoff score for the early detection of upper extremity dysfunction. Study Design: Cross-sectional study. Methods: A total of 86 high school male baseball players were categorized into three groups based on their self-reported J-KJOC: asymptomatic, symptomatic but active, and inactive symptomatic. All participants underwent physical assessments, including shoulder range of motion, isometric shoulder strength, grip strength, and pinch strength measurements. Between-group comparisons, receiver operating characteristic (ROC) analysis, and logistic regression were conducted to determine the discriminative performance of the J-KJOC and its association with physical assessments. Results: The mean age of the participants was 16.3 ± 0.8 years. The J-KJOC scores differed significantly among the three groups (p < 0.01), whereas no significant differences were found in the physical assessments. The ROC analysis revealed a J-KJOC cutoff score of 87.6 with an area under the curve (AUC) of 0.815, yielding 81.5% sensitivity and 72.8% specificity for distinguishing symptomatic players. Logistic regression analysis revealed that only the J-KJOC score, and not conventional physical parameters, was significantly associated with symptoms while playing, across all models. Conclusion: The J-KJOC demonstrated superior sensitivity to conventional physical assessments in detecting upper extremity dysfunction in high school baseball players. A cutoff score of 87.6 may serve as a valuable screening threshold for early intervention and injury prevention in high school baseball athletes. Level of Evidence: Level 3.