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Saito A1, Okada K1, Shibata K2, Sato H3, Kamata T4
1Akita University Graduate School of Health Sciences, Physical Therapy, Akita, Japan, 2Akita City Hospital, Rehabilitation, Akita, Japan, 3Omagari Kousei Medical Center, Rehabilitation, Daisen, Japan, 4Akita Kousei Medical Center, Rehabilitation, Akita, Japan
Background: Repetitive elbow valgus stress during throwing is related to medial elbow injuries in youth baseball players. The forearm flexor-pronator muscles are considered to act as a dynamic stabilizer against the stress. Although the previous study reported the elasticity of the pronator teres (PT) of the throwing arm was high, conditions of other flexor-pronator muscles have not been clarified. Moreover, factors related to muscle elasticity in youth baseball players is poorly understood.
Purpose: To clarify the relationship between elasticity of the forearm flexor-pronator muscles and medial elbow injuries in youth baseball players, and to analyze factors related to them.
Methods: The medial injury group, 47 individuals with medial epicondylar fragmentation (mean age, 11.0 years); and the control group, 90 healthy individuals (mean age, 11.2 years) were enrolled. The elasticities of the PT, flexor carpi ulnaris (FCU), and flexor digitorum superficialis (FDS) of the throwing arm were measured on ultrasound elastography (Noblus, Hitachi Ltd., Japan) in sitting position at 30° elbow flexed and forearm supinated position. The strain ratio (SR) which was the ratio of strain of each muscle to that of the acoustic coupler (EZU-TEATC1, Hitachi Ltd., Japan) was used as the index of the elasticity. A higher SR indicates a harder muscle. Range of motion (ROM) of the shoulder external rotation (ER)/internal rotation (IR) with the arm elevated to 90° of abduction, forearm pronation/supination, hip ER/IR, and straight leg raising were measured using a standard goniometer. The time on practice per week was asked using a questionnaire. These values for each group were compared using a Student's t-test. Additionally, the relationships between the SR of each muscle and ROM and the time on practice per week were examined by using the Pearson correlation coefficient.
Results: The SRs of the PT and FCU were significantly higher in the medial injury group than in the control group (1.24 ± 0.19 vs. 0.77 ± 0.20, 1.31 ± 0.31 vs. 0.94 ± 0.24, respectively, both P 0.001), but not FDS (0.91 ± 0.19 vs. 0.85 ± 0.21, P = 0.100). The shoulder ER ROM was lower (101.2 ± 9.1° vs. 105.6 ± 11.9°, P = 0.030) and the time on practice per week was longer (10.8 ± 3.8 hour vs. 9.5 ± 3.6 hour, P = 0.048) in the medial injury group than in the control group. The SR of the PT was correlated with the shoulder ER ROM and time on practice per week (r = -0.451, r = 0.359, respectively, both P 0.001). Similarly, the SR of FUC was correlated with the time on practice per week (r = 0.433, P 0.001).
Conclusion(s): Youth baseball players with medial elbow injuries exhibited hardness of the PT and FUC, but not FDS. Hardness of the PT and FCU were correlated with long time practice and limitation of shoulder ER.
Implications: Improvement of hardness/stiffness of the PT and FUC, long practice time, and limitation of shoulder ER may contribute to prevention of medial elbow injuries in youth baseball players.
Keywords: medial elbow injury, flexor-pronator muscles, elastography
Funding acknowledgements: This study was supported by Japan Society for the Promotion of Science Grants-in-Aid for Science Research (KAKENHI) grant number 17K17610.
Purpose: To clarify the relationship between elasticity of the forearm flexor-pronator muscles and medial elbow injuries in youth baseball players, and to analyze factors related to them.
Methods: The medial injury group, 47 individuals with medial epicondylar fragmentation (mean age, 11.0 years); and the control group, 90 healthy individuals (mean age, 11.2 years) were enrolled. The elasticities of the PT, flexor carpi ulnaris (FCU), and flexor digitorum superficialis (FDS) of the throwing arm were measured on ultrasound elastography (Noblus, Hitachi Ltd., Japan) in sitting position at 30° elbow flexed and forearm supinated position. The strain ratio (SR) which was the ratio of strain of each muscle to that of the acoustic coupler (EZU-TEATC1, Hitachi Ltd., Japan) was used as the index of the elasticity. A higher SR indicates a harder muscle. Range of motion (ROM) of the shoulder external rotation (ER)/internal rotation (IR) with the arm elevated to 90° of abduction, forearm pronation/supination, hip ER/IR, and straight leg raising were measured using a standard goniometer. The time on practice per week was asked using a questionnaire. These values for each group were compared using a Student's t-test. Additionally, the relationships between the SR of each muscle and ROM and the time on practice per week were examined by using the Pearson correlation coefficient.
Results: The SRs of the PT and FCU were significantly higher in the medial injury group than in the control group (1.24 ± 0.19 vs. 0.77 ± 0.20, 1.31 ± 0.31 vs. 0.94 ± 0.24, respectively, both P 0.001), but not FDS (0.91 ± 0.19 vs. 0.85 ± 0.21, P = 0.100). The shoulder ER ROM was lower (101.2 ± 9.1° vs. 105.6 ± 11.9°, P = 0.030) and the time on practice per week was longer (10.8 ± 3.8 hour vs. 9.5 ± 3.6 hour, P = 0.048) in the medial injury group than in the control group. The SR of the PT was correlated with the shoulder ER ROM and time on practice per week (r = -0.451, r = 0.359, respectively, both P 0.001). Similarly, the SR of FUC was correlated with the time on practice per week (r = 0.433, P 0.001).
Conclusion(s): Youth baseball players with medial elbow injuries exhibited hardness of the PT and FUC, but not FDS. Hardness of the PT and FCU were correlated with long time practice and limitation of shoulder ER.
Implications: Improvement of hardness/stiffness of the PT and FUC, long practice time, and limitation of shoulder ER may contribute to prevention of medial elbow injuries in youth baseball players.
Keywords: medial elbow injury, flexor-pronator muscles, elastography
Funding acknowledgements: This study was supported by Japan Society for the Promotion of Science Grants-in-Aid for Science Research (KAKENHI) grant number 17K17610.
Topic: Sport & sports injuries; Musculoskeletal: upper limb
Ethics approval required: Yes
Institution: Akita University Graduate School of Health Sciences
Ethics committee: Akita University Graduate School of Health Sciences
Ethics number: 1036
All authors, affiliations and abstracts have been published as submitted.
