Internal impingement of the shoulder: comparison of findings between the throwing and nonthrowing shoulders of college baseball players.
The authors evaluated and compared the findings of gadolinium-enhanced magnetic resonance imaging (MRI) studies of throwing and nonthrowing shoulders in college baseball athletes and contrasted these findings with the clinical examination results. Ten throwing college baseball athletes were prospectively clinically examined for instability, range of motion, impingement signs, and relocation testing, then evaluated with bilateral gadolinium enhanced MRI using the nonthrowing shoulder as a control. All MRIs were performed on a 1.5-Tesla magnet and included routine adduction images and images obtained in abduction and external rotation (ABER). Studies were interpreted by a musculoskeletal radiologist and an orthopaedic surgeon specializing in shoulder surgery. In all shoulders, ABER imaging showed physical contact between the undersurface of the rotator cuff and the posterior superior glenoid. No imaging or physical examination abnormalities were identified in the nonthrowing shoulders. Three of 10 throwing shoulders had superior labral tears and adjacent paralabral cysts extending toward or into the spinoglenoid notch. Four of 10 throwing shoulders had abnormal signal change in the rotator cuff tendons. No correlation was identified between positive MRI findings and instability on physical examination. Physical contact between the rotator cuff undersurface and the subjacent labrum can be seen normally in the ABER position. Abnormalities of the rotator cuff and superior labrum are seen in asymptomatic throwing shoulders but not nonthrowing shoulders. MRI abnormalities consistent with internal impingement can be seen in asymptomatic patients. Treatment of these abnormalities in young throwing athletes should be approached with caution.