Glenohumeral movements of the involuntary inferior and multidirectional instability.

The glenohumeral movements of the involuntary inferior and multidirectional instability were studied by means of cineradiography. Using the devised two parameters, i.e., the shoulder center edge and glenoid angles, the author compared the glenohumeral movements of the normal shoulder with the involuntary inferior and multidirectional instability of the shoulder. The glenohumeral movements of the involuntary inferior and multidirectional instability showed not only an excessive excursion and sliding motion but also a deterioration of the scapular abduction and external rotation, with the arm progressively abducted. These phenomena were especially remarkable at the maximum elevation of the arm. The roentgenogram of the overhead view of the shoulder joint indicates whether or not there is an involuntary inferior and multidirectional instability, and whether or not these parameters can be useful for diagnosis of shoulder lesions.