title: Heterogeneous MR arthrography findings in patients with subacromial impingement syndrome - Diagnostic subgroups?
abstract: BACKGROUND
  Subacromial Impingement Syndrome (SIS) is frequently diagnosed, but treatment results vary greatly. It is increasingly reported that SIS symptoms are caused by various underlying mechanisms that need distinctive treatment strategies. We evaluated a set of specific MRI Arthrography (MRA) characteristics that have been related with underlying mechanisms for SIS in the literature, in patients with SIS.
  
  
  METHODS
  In 47 patients diagnosed with SIS, MRA characteristics were evaluated and categorized into categories of potential underlying mechanisms: (1) extrinsic: e.g. acromion shape; (2) intrinsic: e.g. tendinosis; (3) dynamic: e.g. signs of glenohumeral (micro-)instability. Control values were obtained from the literature. With cluster analysis, potential patient subgroups were assessed.
  
  
  RESULTS
  In 17 (36.2%) patients originally diagnosed with SIS, specific other conditions were found, including rotator cuff tears and labrum lesions. In the remaining 30, all had positive signs of at least one of the predefined underlying mechanisms. Patients could be categorized into 2 groups: predominantly findings corresponding with extrinsic/structural causes, or with dynamic/(micro)instability.
  
  
  CONCLUSIONS
  MRA characteristics in patients with SIS symptoms are heterogeneous and many patients have specific other shoulder conditions causing symptoms. Patients without specific other conditions have MRA characteristics associated with either extrinsic (structural), or dynamic (e.g. micro-instability) underlying mechanisms.
authors.affiliation: Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC, Leiden, The Netherlands. Electronic address: P.B.de_Witte@lumc.nl.
authors.forename: Pieter Bas
authors.initials: PB
authors.lastname: de Witte
authors.affiliation: Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC, Leiden, The Netherlands. Electronic address: Celeste_overbeek@hotmail.com.
authors.forename: Celeste L
authors.initials: CL
authors.lastname: Overbeek
authors.affiliation: Department of Radiology, LUMC, Leiden, The Netherlands. Electronic address: A.Navas_Canete@lumc.nl.
authors.forename: Ana
authors.initials: A
authors.lastname: Navas
authors.affiliation: Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC, Leiden, The Netherlands. Electronic address: J.Nagels@lumc.nl.
authors.forename: Jochem
authors.initials: J
authors.lastname: Nagels
authors.affiliation: Department of Radiology, LUMC, Leiden, The Netherlands. Electronic address: M.Reijnierse@lumc.nl.
authors.forename: Monique
authors.initials: M
authors.lastname: Reijnierse
authors.affiliation: Department of Orthopaedics, Leiden University Medical Center (LUMC), Postzone J11R, Postbus 9600, 2300 RC, Leiden, The Netherlands. Electronic address: R.G.H.H.Nelissen@lumc.nl.
authors.forename: Rob G H H
authors.initials: RG
authors.lastname: Nelissen
mesh_terms: D000328:Adult; D001175:Arthrography / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D017006:Rotator Cuff / Q000000981:diagnostic imaging; D000070636:Rotator Cuff Injuries / Q000145:classification / Q000000981:diagnostic imaging / Q000453:epidemiology; D019534:Shoulder Impingement Syndrome / Q000145:classification* / Q000000981:diagnostic imaging* / Q000453:epidemiology; D012785:Shoulder Joint / Q000000981:diagnostic imaging; D052256:Tendinopathy / Q000145:classification / Q000000981:diagnostic imaging / Q000453:epidemiology; D016896:Treatment Outcome
keywords: Cluster analysis; Etiology; Magnetic resonance imaging; Rotator cuff; Shoulder impingement syndrome