title: Abduction and external rotation in shoulder impingement: an open MR study on healthy volunteers initial experience.
abstract: OBJECTIVE
  To prospectively evaluate rotator cuff contact with the glenoid in healthy volunteers placed in the unloaded and loaded abduction and external rotation (ABER) positions in an open magnetic resonance (MR) imager.
  
  
  METHODS
  The study was institutional review board approved and HIPAA compliant, and informed consent was received. Eight male volunteers with no history of shoulder pain or pathology were imaged in a 0.5-T open MR imager. Volunteers were imaged in an unloaded ABER position with the arm at 90 degrees abduction and in a loaded ABER position, with a 1-kg load that produced an average external rotation of 111 degrees+/-6 (standard deviation). Two radiologists graded rotator cuff contact on a three-point scale. Three-dimensional anatomic 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 for the loaded ABER position. Minimum distances were compared by using a paired Student t test.
  
  
  RESULTS
  In the unloaded ABER position, contact was seen between the infraspinatus and supraspinatus tendons and the glenoid in all eight volunteers. In the loaded ABER position, contact was also observed between the infraspinatus and supraspinatus and the posterior and posterosuperior glenoid, respectively. Deformation of the infraspinatus on the glenoid was seen in four volunteers, whereas supraspinatus deformation was only seen in one volunteer. The minimum distance between the supraspinatus insertion and acromion in the loaded ABER position decreased significantly (P<.01). Supraspinatus tendon to glenoid and infraspinatus tendon to glenoid minimum distances also decreased significantly (P<.01).
  
  
  CONCLUSIONS
  The unloaded and loaded ABER positions resulted in contact of the supraspinatus and infraspinatus with the glenoid in all volunteers. Distances between the rotator cuff insertion sites and the glenoid decreased in the loaded ABER position.
authors: Department of Radiology, Stanford University School of Medicine, CA 94305-5105, and Harvard Combined Orthopaedics Program, Department of Orthopaedic Surgery, Massachusetts General Hospital, Boston, MA, USA. gold@stanford.edu
authors: Garry E
authors: GE
authors: Gold
authors: George P
authors: GP
authors: Pappas
authors: Silvia S
authors: SS
authors: Blemker
authors: Sean T
authors: ST
authors: Whalen
authors: Gordon
authors: G
authors: Campbell
authors: Timothy A
authors: TA
authors: McAdams
authors: Christopher F
authors: CF
authors: Beaulieu
mesh_terms: D000328:Adult; D000465:Algorithms; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011446:Prospective Studies; D016059:Range of Motion, Articular; D012399:Rotation; D019534:Shoulder Impingement Syndrome / Q000503:physiopathology*; D012785:Shoulder Joint / Q000502:physiology*