title: Quantitative and qualitative analyses of subacromial impingement by kinematic open MRI.
abstract: OBJECTIVE
  Quantitative and qualitative kinematic analyses of subacromial impingement by 1.2T open MRI were performed to determine the location of impingement and the involvement of the acromioclavicular joint.
  
  
  METHODS
  In 20 healthy shoulders, 10 sequential images in the scapular plane were taken in a 10-s pause at equal intervals from 30° to maximum abduction in neutral and internal rotation. The distances between the rotator cuff (RC) and the acromion and the acromioclavicular joint were measured. To comprehend the positional relationships, cadaveric specimens were also observed.
  
  
  RESULTS
  Although asymptomatic, the RC came into contact with the acromion and the acromioclavicular joint in six and five cases, respectively. The superior RC acted as a depressor for the humeral head against the acromion as the shoulder elevated. The mean elevation angle and distance at the closest position between the RC and the acromion in neutral rotation were 93.5° and 1.6 mm, respectively, while those between the RC and the acromioclavicular joint were 86.7° and 2.0 mm. When comparing this distance and angle, there was no significant difference between the RC to the acromion and to the acromioclavicular joint. The minimum distance between the RC and the acromion was significantly shorter than that between the greater tuberosity and the acromion. The location of RC closest to the acromion and the acromioclavicular joint differed significantly.
  
  
  CONCLUSIONS
  Although asymptomatic, contact was found between the RC and the acromion and the acromioclavicular joint. The important role of the RC to prevent impingement was observed, and hence, dysfunction of the RC could lead to impingement that could result in a RC lesion. The RC lesions may differ when they are caused by impingement from either the acromion or the acromioclavicular joint.
authors: Unit of Clinical Anatomy, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8519, Japan.|Department of Orthopaedic Surgery, St. Luke's International Hospital, Tokyo, Japan.
authors: Atsushi
authors: A
authors: Tasaki
authors: Unit of Clinical Anatomy, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8519, Japan.
authors: Akimoto
authors: A
authors: Nimura
authors: Department of Radiology, St. Luke's International Hospital, Tokyo, Japan.
authors: Taiki
authors: T
authors: Nozaki
authors: Department of Orthopaedic Surgery, St. Luke's International Hospital, Tokyo, Japan.
authors: Akira
authors: A
authors: Yamakawa
authors: Department of Radiology, Saitama Medical College, Moro, Saitama, Japan.
authors: Mamoru
authors: M
authors: Niitsu
authors: Department of Orthopaedic Surgery, St. Luke's International Hospital, Tokyo, Japan.
authors: Wataru
authors: W
authors: Morita
authors: Department of Orthopaedic Surgery, St. Luke's International Hospital, Tokyo, Japan.
authors: Yoshimitsu
authors: Y
authors: Hoshikawa
authors: Unit of Clinical Anatomy, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8519, Japan. akita.fana@tmd.ac.jp.
authors: Keiichi
authors: K
authors: Akita
mesh_terms: D000173:Acromioclavicular Joint / Q000473:pathology*; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D012782:Shoulder / Q000503:physiopathology; D019534:Shoulder Impingement Syndrome / Q000175:diagnosis* / Q000503:physiopathology; D012785:Shoulder Joint / Q000473:pathology* / Q000503:physiopathology; D055815:Young Adult