title: Which shoulder motions cause subacromial impingement? Evaluating the vertical displacement and peak strain of the coracoacromial ligament by ultrasound speckle tracking imaging.
abstract: BACKGROUND
  Subacromial impingement is a common cause of shoulder pain and one cause of rotator cuff disease. We aimed to identify which shoulder motions cause subacromial impingement by measuring the vertical displacement and peak strain of the coracoacromial ligament using ultrasound speckle tracking imaging.
  
  
  METHODS
  Sixteen shoulders without shoulder disability were enrolled. All subjects were men, and the average age was 28.6 years. The vertical displacement and peak strain of the coracoacromial ligament were analyzed by the motion tracing program during the following active assisted motions (active motion controlled by the examiner): (1) forward flexion in the scapular plane, (2) horizontal abduction in the axial plane, (3) external rotation with the arm at 0° abduction (ER0), (4) internal rotation with the arm at 0° abduction (IR0), (5) internal rotation with the arm at 90° abduction (IR90), and (6) internal rotation at the back (IRB).
  
  
  RESULTS
  The mean vertical displacement of the coracoacromial ligament during forward flexion (2.2 mm), horizontal abduction (2.2 mm), and IR90 (2.4 mm) was significantly greater than that during the other motions (ER0, -0.7 mm; IR0, 0.5 mm; IRB, 1.0 mm; P < .003). The mean peak strain was significantly higher in forward flexion (6.88%), horizontal abduction (6.58%), and IR90 (4.88%) than with the other motions (ER0, 1.42%; IR0, 1.78%; IRB, 2.61%; P < .003).
  
  
  CONCLUSIONS
  Forward flexion, horizontal abduction, and IR90 showed higher vertical displacement and peak strain of the coracoacromial ligament, causing subacromial impingement. It is recommended that patients with impingement syndrome or a repaired rotator cuff avoid these shoulder motions.
authors.affiliation: Department of Orthopedic Surgery, Armed Forces Capital Hospital, Bundang-gu, Gyeonggi-do, South Korea.
authors.forename: In
authors.initials: I
authors.lastname: Park
authors.affiliation: Department of Orthopedic Surgery, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
authors.forename: Hyo-Jin
authors.initials: HJ
authors.lastname: Lee
authors.affiliation: Department of Orthopedic Surgery, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
authors.forename: Sung-Eun
authors.initials: SE
authors.lastname: Kim
authors.affiliation: Department of Orthopedic Surgery, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
authors.forename: Sung-Ho
authors.initials: SH
authors.lastname: Bae
authors.affiliation: Department of Orthopedic Surgery, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
authors.forename: Chu-Hwan
authors.initials: CH
authors.lastname: Byun
authors.affiliation: Department of Orthopedic Surgery, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea. Electronic address: kysoos@catholic.ac.kr.
authors.forename: Yang-Soo
authors.initials: YS
authors.lastname: Kim
mesh_terms: D000328:Adult; D006801:Humans; D008023:Ligaments, Articular / Q000000981:diagnostic imaging* / Q000502:physiology; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D012782:Shoulder; D019534:Shoulder Impingement Syndrome / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D013314:Stress, Mechanical; D014463:Ultrasonography
keywords: 2D speckle tracking echocardiography; Coracoacromial ligament; displacement; impingement; in vivo; strain