Abstract:
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Purpose: The abduction external rotation (ABER) shoulder position is associated with internal glenoid impingement and rotator cuff pathology in overhead athletes. However, the existence of internal impingement in normal subjects has not been established. The goal of this study was to characterize shoulder anatomy and rotator cuff impingement in normal subjects placed in the ABER position.
Methods and Materials: Eight normal male volunteers (19-21 years) with no history of shoulder pain/pathology were imaged with fast, 3D gradient echo sequences in two orthogonal planes in a 0.5T open MRI scanner. Subjects were positioned in a true ABER position with the arm at 90 degrees of abduction, similar to the apprehension test position for shoulder instability. Two radiologists visually graded rotator cuff impingement and 3D anatomical models generated from the MR images were used to measure distances. Minimum distances were computed between the tendon insertion sites and the glenoid, acromion, and coracoid. Subjects were imaged in a loaded ABER position (a 1-kg load applied at the wrist produced an external rotation of 111 +/- 6 degrees).
Results: In the loaded ABER position, the supraspinatus impinged against the coracoacromial arch in only one subject. In all subjects, however, contact was observed between the infraspinatus and supraspinatus and the posterior- and posterosuperior-glenoid, respectively. Mechanical impingement on the glenoid, with not only contact, but also deformation of the infraspinatus tendon, was seen in 4/8 subjects; supraspinatus-glenoid impingement was seen in only one subject. The minimum distance between the supraspinatus insertion and acromion (16.9 +/- 4.8 mm in neutral position) decreased significantly to 5.7 +/-3.0 mm. Supraspinatus-glenoid distance (35.0 +/- 2.8 mm in neutral) decreased substantially and significantly to 6.6 +/- 3.6 mm; infraspinatus-glenoid distance (38.4 +/- 2.4 mm in neutral) also decreased significantly to 3.6 +/- 1.7 mm.
Conclusion: The ABER position resulted in contact of the supraspinatus and infraspinatus with the glenoid in all subjects, with infraspinatus impingement and tendon deformation observed in half of the subjects. Distances between the rotator cuff insertion sites and the glenoid decreased substantially, suggesting that internal impingement occurs in normal subjects placed in the ABER position.
Questions about this event email: gold@stanford.edu
Gold MD, MSEE, G,
Abduction and External Rotation in Shoulder Impingement: An Open MRI Study. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3105127.html
