title: The effect of scapular position on subacromial contact behavior: a cadaver study.
abstract: BACKGROUND
  Patients with subacromial impingement were reported to show abnormal scapular positions during shoulder elevation. However, the relationship between the scapular positions and subacromial impingement is unclear. The purpose of this study was to biomechanically determine the effect of scapular position on subacromial contact behavior by using fresh frozen cadavers.
  
  
  METHODS
  The peak contact pressure on the coracoacromial arch was measured with a flexible tactile force sensor in 9 fresh frozen cadaver shoulders. The measurement was performed during passive glenohumeral elevation in the scapular plane ranging from 30° to 75°. The scapular downward and internal rotations and anterior tilt were simulated by tilting the scapula in 5° increments up to 20°. The measurement was also performed with combination of scapular downward and internal rotations and anterior tilt positions.
  
  
  RESULTS
  The peak contact pressure decreased linearly with anterior tilt, and a significant difference between neutral scapular position (1.06 ± 0.89 MPa) and anterior tilt by 20° (0.46 ± 0.18 MPa) was observed (P < .05). However, the scapular positioning in the other directions did not change the peak contact pressure significantly. Furthermore, any combination of abnormal scapular positions did not affect peak contact pressure significantly.
  
  
  CONCLUSIONS
  Scapular anterior tilt decreased peak contact pressure during passive shoulder elevation. In addition, scapular downward and internal rotations had little effect on peak contact pressure. The abnormal scapular motion reported in previous studies might not be directly related to symptoms caused by subacromial impingement.
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, MN, USA.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Muraki
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, MN, USA.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Yamamoto
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA.
authors.forename: John W
authors.initials: JW
authors.lastname: Sperling
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA.
authors.forename: Scott P
authors.initials: SP
authors.lastname: Steinmann
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Cofield
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA. Electronic address: an.kainan@mayo.edu.
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D012540:Scapula / Q000502:physiology*; D019534:Shoulder Impingement Syndrome / Q000503:physiopathology; D012785:Shoulder Joint / Q000502:physiology*
keywords: Cadaver; contact pressure; passive shoulder motion; scapular position; shoulder; subacromial impingement