[An MR-based technique for determination of the subacromial space width in subjects with and without shoulder muscle...

The occurrence of the impingement syndrome of the shoulder is dependent on muscle activity and arm position. However, the current radiological workup is based on conventional radiographs, CT or MRI obtained at 0 degree of abduction and at muscular relaxation. The objective of this study was the development of a technique for simultaneous visualization of the humerus, scapula, clavicle and their relationship to the M. supraspinatus--in different arm abduction positions with and without muscle activity--as well as the determination of the minimal acromio-humeral distance.

The shoulder joints of 8 volunteers were examined in an open MRI system at 60 degrees, 90 degrees and 120 degrees of abduction, using a T1 weighted 3D gradient echosequence. Forces of 10 N were applied at the distal humerus. After 3D reconstruction, the acromio-humeral distance was computed with Euclidian distance transformation.

With increasing abduction, the acromio-humeral distance decreased significantly (p < 0.05), but the distance vector was localised laterally to the M. supraspinatus at 120 degrees. With muscle activity a reduction of the subacromial space of 29% (p < 0.05) occurred at 60 degrees whereas at 120 degrees a 51% (p < 0.05) increase was noted. At 90 degrees, no significant difference was observed.

With the technique presented it is possible to determine the subacromial space width in different arm positions independent of the specific section orientation, with and without muscle activity. The method can be used as a basis for biomechanical investigations and for the clinical diagnosis of impingement syndrome.