• Journal of Korean Orthopaedic Sports Medicine
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• v.2 no.1
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• pp.62-70
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• 2003

Purpose: We examined the kinematics and kinetics of the shoulder in youth baseball pitchers in light of the mechanisms of development of little league shoulder and humeral retrotorsion. Materials and Methods: The joint kinematics and the net force and torque acting on the humerus were calculated in fourteen youth pitchers throwing in a simulated game. Results: The major force component acting on the humerus was a tensile force of 378$\pm$81 N that peaked just after ball release. The predominant torque on the humerus was an external rotation torque about the long axis of the humerus. This torque reached a peak value of 35.3$\pm$6.7 Nm about 73$\%$through the pitching motion. This torque is approximately 66$\%$ of the torque required to fracture of the adult humerus. Conclusions: The direction of the humeral torque was consistent with the development of increased humeral retrotorsion in the throwing arm. Shear stress arising from the high torque during the late cocking phase likely leads to deformation the relatively weak proximal humeral epiphysis. The external rotation torque applied to the humerus during the pitch also agrees with the proposed mechanism for development little league shoulder, which has been hypothesized to be due to rotational stresses acting on the epiphysis during the throwing motion.

• The Journal of Korean Orthopaedic Ultrasound Society
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• v.7 no.2
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• pp.89-97
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• 2014

Purpose: To evaluate the ultrasonographic findings of the elbows on group screening of middle school baseball players. Materials and Methods: Ninety-three players (age: 12-15, mean 13.5 years) of four middle school baseball team were evaluated with bilateral elbow ultrasonographies in the field regardless of elbow pain. Medial and anterolateral ultrasound examination of the both elbow were performed in the field to detect any abnormalities including medial epicondylar separation or fragmentation and capitellar osteochondritis dissecans respectively. We analyzed the relationship among elbow pain, physical findings and sonographic abnormalities and the differences of sonographic abnormalities between pitchers and fielders. Results: Thirty-six of 93 (39%) players had sonographic abnormalities of elbow in dominant arm, 30 with medial epicondylar apophyseal separation or fragmentation, 2 with osteochondritis dissecans, 4 with both lesions. Twenty-nine of 37 (78%) players with elbow pain had sonographic abnormalities. On physical examination, players with medial epicondylar abnormalities had medial epicondylar tenderness (59%) and pain on valgus stress test (52%), and 5 of 6 (83%) players with osteochondritis dissecans showed flexion contracture more than $5^{\circ}$. The incidence of medial epicondylar abnormalities between pitchers and fielders was statistically not significant but osteochondritis dissecans was more prevalent in pitchers (p<0.05). Conclusion: Elbow sonography is a simple and useful screening tool in the field and also effective for early detection of medial epicondylar abnormalities or osteochondritis dissecans that could be the main causes of elbow pain in adolescent baseball players.