Abstract:

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.

Key words: Shoulder, Stability, Humeral head, Defect