The Prevalence and Clinical Characteristics of Medial Epicondyle Apophysitis in Juvenile Baseball Player - Ultrasonographic Assessment of 2,926 Cases

OBJECTIVES: Apophysitis of humeral medial epicondyle, often referred to as “Little Leaguer’s Elbow, is one of the major throwing injuries in juvenile baseball players as common as osteochondritis dissecans of humeral capitellum. Repetitive valgus stress to the skeletally immature elbow can result in fragmentation, hypertrophy, or separation of the medial epicondyle apophysis, and these injuries may induce elbow pain and adversely influence on elbow function and throwing performance. Although several reports have described various morphological variations of the medial epicondyle apophysis, little is known about the natural course and clinical significance of these variations. The purpose of this study was to investigate the prevalence of these variations in each age group and clarify the association with elbow pain using the large epidemiologic data from medical check-ups of juvenile baseball players. METHODS: Of 3,626 juvenile baseball players aged 6 to 17 years, 2,926 players were enrolled in this study. Experience of elbow pain was rated by self-completed questionnaires. Ultrasonographic assessment was used to assess the morphological variations of the antero-inferior medial epicondyle (MEC) and humeral capitellum. Regarding MEC lesion, enthesis of medial ulnar collateral ligament (MUCL) was classified into four types: normal, irregular (IR), fragmentation (FG), and hypertrophy (HT). Osteochondral lesion (OCL) of humeral capitellum was judged by the irregularity or fragmentation of subchondral bone. The prevalence of these lesions was investigated in each age group and evaluated the influence on elbow pain using multivariable logistic regression analysis. RESULTS: The overall prevalence of MEC lesions and capitellum OCL was 49.9% (IR:6.7%, FG:11.7%, HT:31.5%) and 2.1%, respectively. The prevalence of IR and FG gradually increased until reaching its highest at 11-12 years of age. At 12-17 years of age, the prevalence of IR was decreased with age, whereas that of FG persisted at approximately 10% after a temporally decrease. Conversely, the prevalence of HT increased while those of IR and FG simultaneously decreased (Figure 1). Age- and position adjusted multivariable analysis revealed that the presence of MEC lesions were high risk of elbow pain, and significantly higher risk for FG (odds ratio [OR]: 4.25, 95% confidence interval [CI]: 3.23-5.62) compared to IR (OR:3.17, 95%CI:2.31-4.39) and HT (OR:2.12, 95%CI:1.76-2.55). Capitellum OCL of was also significantly high risk of elbow pain (OR:,2.69, 95%CI:1.42-5.45) (Table 1). CONCLUSION: Our study demonstrated that morphology of MEC apophysis in juvenile baseball player varied with age. As the presence of FG was a significantly high- risk factor for elbow pain as compared to HT, appropriate management of “Little Leaguer’s Elbow” in the preadolescent period might be quite important to accelerate the bony healing of medial epicondyle apophysitis and decrease preventable adulthood elbow pain.