Computed arthrotomography of the shoulder: comparison of examinations made with internal and external rotation of the humerus

Department of Radiology, University of Michigan, University Hospitals, Ann Arbor 48109-0326.

We assessed the best positioning of the humerus for CT scans obtained after air-contrast shoulder arthrography by performing 54 examinations with both external and internal rotation of the humerus. Of the 30 abnormalities of the anterior portion of the labrum, 27 (90%) were identified on the scans obtained with the arm in internal rotation. The other three (10%) were shown best or solely on the scans obtained with the arm in external rotation. All 22 abnormalities of the anterior capsule were shown on the scans obtained with internal rotation. In no case were scans obtained in external rotation superior. Five posterior labral and capsule abnormalities were found; two of them were identified best or only on scans obtained with external rotation. The other three were shown equally well with the arm in either position. The results show that a modest (9%) increase in diagnostic yield can be expected when CT scans obtained with the arm in external rotation are added to studies performed solely with the arm internally rotated.
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