目的　探讨肱骨头缺损对肩关节稳定性影响的程度。  方法　8例16侧肩关节的肱骨头后方缺损程度分别设成全部肱骨头的1/8、2/8、3/8、4/8，各4侧标本。检测指标分别为45°和90°外展、40°内旋、中立位、40°外旋等5个指标。检测个缺损的肱骨头由小到大各个角度的外展、内外旋同时作用的结果。肱骨头在各个合力作用下缓慢向前外侧推动，直到脱位。记录肱骨头所移动的距离（distance of 　dislocation，DD），并作为基本分析数据。  结果    外展角度比较，DD无显著性差异。但外旋40°与中立为和40°内旋比较，有显著性差异。在3/8缺损组，外旋40°外展90°时，DD明显减小。4/8组，外展90°与中立位时，DD均明显减小。而内旋40°者，各组DD未见明显减小。  结论    肱骨头缺损3/8时，当肩关节外展外旋时，肩关节稳定性下降；而当肱骨头缺损4/8时，肩关节中立位和外旋位均会发生关节不稳。

Objective　To explore anatomic relationship between the degree of humeral head defect and glenohumeral stability.　Methods　12 cadaveric shoulder specimens were applied in this study. The defect scopes of humeral head were prepared as 1/8, 2/8, 3/8, and 4/8. Testing positions included 45° and 90° of abduction, 40° of internal rotation, neutral position, and 40° of external rotation. The humeral head was translated anteroinferiorly to the horizontal glenoid axis until its dislocation. The distance of dislocation (DD) was defined as humeral head translation.　Results　At the abduction position, there was no difference of the DD for different defects. However, external rotation of 40° significantly reduced the DD compared to that of neutral and 40° internal rotation. The defect of 3/8 and 4/8 significantly decreased the DD compared to that of intact ones. Post hoc analysis determined significant difference for the rotational positions. Decreased distance to dislocation occurred at 2/8 defect group at 40° external rotation with 90° of abduction. For the 4/8 defect at 90°abduction, the DD decreased compared to that of neutral and 40°external rotation; At the position of 45° abduction and 40° external rotation, the DD significantly decreased. At the 40° internal rotation, no significant difference appeared among different defect groups.　Conclusions　Glenohumeral stability decreases at the 3/8 defect and at external rotation and abduction, however, at the 4/8 defect and at neutral and external rotation, the stability further decreases.