title: An evidence-based review of current perceptions with regard to the subacromial space in shoulder impingement syndromes: Is it important and what influences it?
abstract: BACKGROUND
  Reduction of the subacromial space as a mechanism in the etiology of shoulder impingement syndromes is debated. Although a reduction in this space is associated with shoulder impingement syndromes, it is unclear if this observation is cause or consequence.
  
  
  METHODS
  The purposes of this descriptive review are to provide a broad perspective on the current perceptions with regard to the pathology and pathomechanics of subacromial and internal impingement syndromes, consider the role of the subacromial space in impingement syndromes, describe the intrinsic and extrinsic mechanisms considered to influence the subacromial space, and critique the level of evidence supporting these concepts.
  
  
  RESULTS
  Based on the current evidence, the hypothesis that a reduction in subacromial space is an extrinsic cause of impingement syndromes is not conclusively established and the evidence permits no conclusion.
  
  
  CONCLUSIONS
  If maintenance of the subacromial space is important in impingement syndromes regardless of whether it is a cause or consequence, research exploring the correlation between biomechanical factors and the subacromial space, using the later as the outcome measure, would be beneficial.
authors.affiliation: Salford University, Health, Sports and Rehabilitation Sciences, Manchester, United Kingdom/M5 4WT. Electronic address: t.a.mackenzie@edu.salford.ac.uk.
authors.forename: Tanya Anne
authors.initials: TA
authors.lastname: Mackenzie
authors.affiliation: Salford University, School of Sport, Exercise and Physiotherapy, Salford, Manchester, United Kingdom. Electronic address: l.c.herrington@salford.ac.uk.
authors.forename: Lee
authors.initials: L
authors.lastname: Herrington
authors.affiliation: English Institute of Sport, Manchester,UK. Electronic address: Ian.Horsley@eis2win.co.uk.
authors.forename: Ian
authors.initials: I
authors.lastname: Horlsey
authors.affiliation: Ghent University Dept of Rehabilitation Science and Physiotherapy, Ghent, Belgium. Electronic address: AnnCools@UGent.Be.
authors.forename: Ann
authors.initials: A
authors.lastname: Cools
mesh_terms: D000174:Acromion; D001696:Biomechanical Phenomena; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology; D017006:Rotator Cuff / Q000502:physiology; D019534:Shoulder Impingement Syndrome / Q000209:etiology / Q000503:physiopathology*
keywords: Acromiohumeral distance; Biomechanical mechanisms; Rotator cuff impingement; Shoulder impingement; Ubacromial space