Simulated humeral avulsion of the glenohumeral ligaments: a new instability model.

Humeral avulsion of the glenohumeral ligaments (HAGL) is an infrequent cause of shoulder instability. Experimental studies on this lesion are rare. This study was undertaken to determine the extent of humeral-based capsuloligamentous damage required for dislocation to occur. In 65 fresh cadaver shoulders, a humeral-sided ligamentous cutting sequence was done. After each step, degree of sulcus, translation, and instability were evaluated with an electromagnetic tracking device. There was a high degree of correlation between the amount of cut done and the resulting degree of instability. The order of the ligamentous cuts had no significant influence. For a dislocation to occur at least 3 zones had to be cut. Simulated HAGL can be used as a model for shoulder instability, although further experiments are needed to validate this model fully. Extensive capsuloligamentous lesions on the humeral side seem to be required before dislocation can occur. This may be a factor explaining the relative paucity of HAGL in clinical series.