title: Study protocol subacromial impingement syndrome: the identification of pathophysiologic mechanisms (SISTIM).
abstract: BACKGROUND
  The subacromial impingement syndrome (SIS) is the most common diagnosed disorder of the shoulder in primary health care, but its aetiology is unclear. Conservative treatment regimes focus at reduction of subacromial inflammatory reactions or pathologic scapulohumeral motion patterns (intrinsic aetiology). Long-lasting symptoms are often treated with surgery, which is focused at enlarging the subacromial space by resection of the anterior part of the acromion (based on extrinsic aetiology). Despite that acromionplasty is in the top-10 of orthopaedic surgical procedures, there is no consensus on its indications and reported results are variable (successful in 48-90%). We hypothesize that the aetiology of SIS, i.e. an increase in subacromial pressure or decrease of subacromial space, is multi-factorial. SIS can be the consequence of pathologic scapulohumeral motion patterns leading to humerus cranialisation, anatomical variations of the scapula and the humerus (e.g. hooked acromion), a subacromial inflammatory reaction (e.g. due to overuse or micro-trauma), or adjoining pathology (e.g. osteoarthritis in the acromion-clavicular-joint with subacromial osteophytes).We believe patients should be treated according to their predominant etiological mechanism(s). Therefore, the objective of our study is to identify and discriminate etiological mechanisms occurring in SIS patients, in order to develop tailored diagnostic and therapeutic strategies.
  
  
  METHODS
  In this cross-sectional descriptive study, applied clinical and experimental methods to identify intrinsic and extrinsic etiologic mechanisms comprise: MRI-arthrography (eligibility criteria, cuff status, 3D-segmented bony contours); 3D-motion tracking (scapulohumeral rhythm, arm range of motion, dynamic subacromial volume assessment by combining the 3D bony contours and 3D-kinematics); EMG (adductor co-activation) and dynamometry instrumented shoulder radiographs during arm tasks (force and muscle activation controlled acromiohumeral translation assessments); Clinical phenotyping (Constant Score, DASH, WORC, and SF-36 scores).
  
  
  CONCLUSIONS
  By relating anatomic properties, kinematics and muscle dynamics to subacromial volume, we expect to identify one or more predominant pathophysiological mechanisms in every SIS patient. These differences in underlying mechanisms are a reflection of the variations in symptoms, clinical scores and outcomes reported in literature. More insight in these mechanisms is necessary in order to optimize future diagnostic and treatment strategies for patients with SIS symptoms.
  
  
  BACKGROUND
  Dutch Trial Registry (Nederlands Trial Register) NTR2283.
authors.affiliation: Department of Orthopaedics, Leiden University Medical Centre, Postzone J11R, Postbus 9600, 2300 RC Leiden, The Netherlands. P.B.de_Witte@lumc.nl
authors.forename: Pieter Bas
authors.initials: PB
authors.lastname: de Witte
authors.forename: Jochem
authors.initials: J
authors.lastname: Nagels
authors.forename: Ewoud R A
authors.initials: ER
authors.lastname: van Arkel
authors.forename: Cornelis P J
authors.initials: CP
authors.lastname: Visser
authors.forename: Rob G H H
authors.initials: RG
authors.lastname: Nelissen
authors.forename: Jurriaan H
authors.initials: JH
authors.lastname: de Groot
mesh_terms: D000328:Adult; D001175:Arthrography; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D004576:Electromyography; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D053581:Muscle Strength Dynamometer; D009426:Netherlands; D011379:Prognosis; D016059:Range of Motion, Articular; D012107:Research Design; D018570:Risk Assessment; D012307:Risk Factors; D017006:Rotator Cuff / Q000503:physiopathology*; D019534:Shoulder Impingement Syndrome / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology* / Q000628:therapy; D012785:Shoulder Joint / Q000503:physiopathology*