title: Glenohumeral translation in ABER position during muscle activity in patients treated with Latarjet procedure: an in vivo MRI study.
abstract: OBJECTIVE
  The Latarjet procedure is frequently performed when treating traumatic anteroinferior shoulder instability. This procedure is supposed to have a triple effect: osseous, muscular and ligamentous. The main stabilizing mechanism in cadaver studies on fresh-frozen shoulders seems to be the sling effect produced by the subscapularis and the conjoint tendon. It has been hypothesized that muscle contraction in ABER position (abduction-external rotation) is able to translate the humeral head posteriorly and superiorly due to the sling effect. The aim of this study was to analyse the humeral head translation relative to the glenoid with the arm in ABER position with and without muscle contraction.
  
  
  METHODS
  Twenty-one subjects divided into two groups (Group A: after Latarjet; Group B: healthy subjects) were examined with an open MRI system with the shoulder in abduction-external rotation (ABER) position to analyse humeral head translation during muscle activity.
  
  
  RESULTS
  In normal shoulders, there was no significant difference in anteroposterior or superoinferior translation between the rest position and the muscle-activated state. In subjects after the Latarjet procedure, the difference was significant and was also significant between both groups of subjects for posterior translation, but not for superior translation.
  
  
  CONCLUSIONS
  In patients treated with Latarjet procedure, there are significant changes in glenohumeral translation during muscular activity when in ABER position, with the humeral head going more posteriorly, in comparison with normal shoulders. This study confirms the stabilizing sling effect of the transposed conjoint tendon in the ABER position.
  
  
  METHODS
  Retrospective case-control study, Level III.
authors.affiliation: Department of Orthopaedic Surgery, Concordia Hospital for "Special Surgery", Via delle Sette Chiese 90, 00145, Rome, Italy. concordia@iol.it.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Di Giacomo
authors.affiliation: Department of Orthopaedic Surgery, Concordia Hospital for "Special Surgery", Via delle Sette Chiese 90, 00145, Rome, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Scarso
authors.affiliation: Department of Orthopaedic Surgery, Concordia Hospital for "Special Surgery", Via delle Sette Chiese 90, 00145, Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: De Vita
authors.affiliation: Department of Radiology, Universita' di Roma "La Sapienza", Rome, Italy.
authors.forename: Mario A
authors.initials: MA
authors.lastname: Rojas Beccaglia
authors.affiliation: Department of Orthopaedic Surgery, Universitair Ziekenhuis, Vrije Universiteit Brussel, Laarbeeklaan 101, 1090, Brussels, Belgium.
authors.forename: Nicole
authors.initials: N
authors.lastname: Pouliart
authors.affiliation: Department of Orthopaedic Surgery, Concordia Hospital for "Special Surgery", Via delle Sette Chiese 90, 00145, Rome, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: de Gasperis
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D016025:Bone Transplantation / Q000379:methods*; D002102:Cadaver; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D058430:Humeral Head / Q000503:physiopathology; D007593:Joint Instability / Q000503:physiopathology* / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D012399:Rotation; D012540:Scapula / Q000503:physiopathology / Q000601:surgery*; D012785:Shoulder Joint / Q000503:physiopathology* / Q000601:surgery*; D013710:Tendons / Q000503:physiopathology
keywords: Instability; Latarjet; MRI; Shoulder; Translation