Type II superior labrum anterior-posterior (SLAP) lesion is a common injury for throwers as well as increased anterior shoulder capsuloligamentous laxity. However there is no biomechanical study of the effects of type II SLAP lesion with increased shoulder capsuloligamentous laxity. The purpose of this study was to investigate the effects of an experimentally created type II SLAP lesion, and anterior capsuloligamentous laxity on glenohumeral translation and rotational range of motion. Six fresh frozen cadaveric shoulders were tested using a custom shoulder testing system and Microscribe. Excessive humeral external rotation (20% beyond the maximum external rotation)was applied at 60°of glenohumeral abduction to yield a detachment of superior labrum and an elongation of anterior shoulder capsule. The experimentally created type II SLAP lesions were then repaired arthroscopically. The rotational range of motion was measured at 60°glenohumeral abduction. Glenohumeral translations were measured at O,30 and 60°glenohumeral abduction in neutral rotation and 90°extemal rotation. External rotation was significantly increased by 20.8±2.1°after excessive external rotation and decreased by only 4.0±0.7°after a SLAP repair. Anterior and tnferior translations were significantly increased at all positions after excessive external rotation and decreased at 30°glenohumeral abduction and neutral rotation and at O°glenohumeral abduction and neutral rotation, respectively, after SLAP repair. All experimentally created type II SLAP lesions were associated with elongation of the anterior capsular ligaments. For a type II SLAP lesion with anterior shoulder instability or anterior pathologic laxity at 90°of shoulder abduction(60°glenohumeral abduction), as seen in throwers, an increased external rotation and an increased anterior and inferior shoulder joint laxity at 90°shoulder abduction may be due primarily to elongation of the anterior capsular ligaments. Therefore, anterior shoulder ligamentous laxity should be addressed in addition to SLAP repair.
