title: Supraspinatus tendon and subacromial space parameters measured on ultrasonographic imaging in subacromial impingement syndrome.
abstract: OBJECTIVE
  To characterize the supraspinatus tendon thickness, subacromial space, and the relationship between tendon thickness and subacromial space to further elucidate the mechanisms of subacromial impingement syndrome.
  
  
  METHODS
  In a single-blind cross-sectional study, subjects were recruited with subacromial impingement syndrome (n = 20) and asymptomatic controls (n = 20) matched for age, gender, and hand dominance. Ultrasound images were collected using a 4-12-MHz linear transducer in B-mode of the supraspinatus tendon in the transverse (short axis) and the anterior aspect of the subacromial space outlet. Using image callipers, measurements of tendon thickness were taken at 3 points along the tendon and averaged for a single thickness measure. The subacromial space outlet was measured via the acromiohumeral distance (AHD) defined by the inferior acromion and superior humeral head. The occupation ratio was calculated as the tendon thickness as a percentage of AHD.
  
  
  RESULTS
  The subacromial impingement syndrome group had a significantly thicker tendon (mean difference = 0.6 mm, p = 0.048) and a greater tendon occupation ratio (mean difference = 7.5 %, p = 0.014) compared to matched controls. There were no AHD group differences.
  
  
  CONCLUSIONS
  The supraspinatus tendon was thicker and occupied a greater percentage of AHD, supporting an intrinsic mechanism. An extrinsic mechanism of tendon compression is theoretically supported, but future imaging studies need to confirm direct compression with elevation. Treatment to reduce tendon thickness may reduce symptoms, and surgical intervention to increase subacromial space may be considered if tendon compression can be verified.
authors.affiliation: COOR Laboratory, Department of Physical Therapy, Virginia Commonwealth University, Rm 100, West Hospital Basement, Richmond, VA, 23298, USA, lamichen@vcu.edu.
authors.forename: Lori A
authors.initials: LA
authors.lastname: Michener
authors.forename: Sevgi S
authors.initials: SS
authors.lastname: Subasi Yesilyaprak
authors.forename: Amee L
authors.initials: AL
authors.lastname: Seitz
authors.forename: Mark K
authors.initials: MK
authors.lastname: Timmons
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Walsworth
mesh_terms: D000174:Acromion / Q000000981:diagnostic imaging*; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D058430:Humeral Head / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D017006:Rotator Cuff / Q000000981:diagnostic imaging*; D019534:Shoulder Impingement Syndrome / Q000000981:diagnostic imaging*; D016037:Single-Blind Method; D014463:Ultrasonography