投球時に上腕骨内顆骨折と肘関節脱臼を受傷したリトルリーガーの1例

Elbow Dislocation and Medial Condylar Fracture of the Humerus in a Little Leaguer Induced by Baseball Throwing. Case Report

　投球動作により上腕骨内顆骨折と肘関節脱臼を受傷した10歳男児のリトルリーガーの稀な1例を経験した．滑車核出現以前であったため，単純X線所見による上腕骨内顆骨折の確定診断は困難であったが，肘関節造影および，MRI検査が診断に有用であった．骨折型はMilch TypeⅠに分類され，Kirschner鋼線を用いてZuggurtung法で固定した．発傷機転としては，第1に局所的には投球動作時における肘関節への外反ストレスと屈筋群の骨端部への牽引力，肘頭から滑車部への剪断力，そして滑車核が生じる以前の骨端部の物理的な脆弱性が考えられた．第2に運動連鎖の観点からは，下肢体幹筋力の低下，筋柔軟性の低下が投球時に肘関節の負荷を増大させたことが考えられた．

　We report a rare case of elbow dislocation and medial condylar fracture of the humerus in a 10-year-old little leaguer boy that were induced by baseball throwing.　It was difficult to diagnose the fracture on radiographs because the epiphysis of the medial condyle of the humerus had not developed, however, arthrography and MRI were useful in making the diagnosis.　The fracture was classified as Milch Type I, and treatment consisted of open reduction and internal fixation (ORIF) by tension band wiring.　The injury may have been caused by valgus stress and traction force exerted by the flexor muscles on the medial epiphyseal region of the elbow during the accelerating phase and by shearing force from the olecranon to the trochlea in the follow-through phase and the mechanical fragilility of the epiphyseal region before the epiphyseal nucleus had developed.　From a kinetic chain standpoint, it appeared that muscle weakness and poor flexibility of the lower extremity and trunk may have placed an excessive load on the elbow during the throwing cycle.