The purpose of this study was to clarify the CT-Arthrographic features of MDI in more detail. Bilateral shoulders in 13 patients with MDI were studied as well as 13 normal shoulders with no laxity as controls. The average age of the MDI patients was 17.9 years and they consisted of two men and 11 women. The average age of the controls was 18.2 years and they consisted of three men and ten women. CT-Arthrography was done by the double contrast method(slice thickness: 5 mm, gap: -2mm). To clarify the characteristic findings on CT-Arthrography, we compared the symptomatic shoulders of the MDI patients with those of the controls. The MDI patients had a flat subchondral bony glenoid, bony hypoplasia of the posteroinferior glenoid rim, and expansion of the capsule and rotator interval. A small Hill-Sachs lesion and reverse Hill-Sachs lesion were also seen in the patients with a traumatic onset. The glenohumeral index and glenoid tilting angle were not significantly different between the two groups. To determine whether these findings were unique to the symptomatic shoulder of the MDI patients or not, we also made a comparison with the asymptomatic side. There were no differences between the symptomatic and asymptomatic sides except for the Hill-Sachs lesion and reverse Hill-Sachs lesion.
Not only soft tissue abnormalities but also bony development may be involved in the mechanism of MDI. Since these findings were also in the asymptomatic side of the MDI shoulder, the developmental factor might be thought to be their cause.
