title: Importance of a three-dimensional measure of humeral head subluxation in osteoarthritic shoulders.
abstract: OBJECTIVE
  During total shoulder arthroplasty (TSA), humeral head subluxation may be difficult to manage. Furthermore, there is a risk for postoperative recurrence of subluxation, affecting the outcome of TSA. An accurate evaluation of the subluxation is necessary to evaluate this risk. Currently, subluxation is measured in 2 dimensions (2D), usually relative to the glenoid face. The goal of this study was to extend this measure to 3 dimensions (3D) to compare glenohumeral and scapulohumeral subluxation and to evaluate the association of subluxation with the glenoid version.
  
  
  METHODS
  The study analyzed 112 computed tomography scans of osteoarthritic shoulders. We extended the usual 2D definition of glenohumeral subluxation, scapulohumeral subluxation, and glenoid version by measuring their orientation in 3D relative to the scapular plane and the scapular axis. We evaluated statistical associations between subluxation and version in 2D and 3D.
  
  
  RESULTS
  Orientation of subluxation and version covered all sectors of the glenoid surface. Scapulohumeral subluxation and glenoid version were highly correlated in amplitude (R(2) = 0.71; P < .01) and in orientation (R(2) = 0.86; P < .01). Approximately every degree of glenoid version induced 1% of scapulohumeral subluxation in the same orientation of the version. Conversely, glenohumeral subluxation was not correlated to glenoid version in 2D or in 3D.
  
  
  CONCLUSIONS
  Orientation of the humeral subluxation is rarely within the arbitrary computed tomography plane and should therefore be measured in 3D to detect out-of-plane subluxation. Scapulohumeral subluxation and glenoid version measured in 3D could bring valuable information for decision making during TSA.
authors.affiliation: Laboratory of Biomechanical Orthopedics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland. Electronic address: alexandre.terrier@epfl.ch.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Terrier
authors.affiliation: Laboratory of Biomechanical Orthopedics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Julien
authors.initials: J
authors.lastname: Ston
authors.affiliation: Service of Orthopaedics and Traumatology, University Hospital Center and University of Lausanne, Lausanne, Switzerland.
authors.forename: Alain
authors.initials: A
authors.lastname: Farron
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D019643:Arthroplasty, Replacement; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D058430:Humeral Head / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000150:complications / Q000000981:diagnostic imaging / Q000601:surgery; D011184:Postoperative Period; D012189:Retrospective Studies; D012783:Shoulder Dislocation / Q000150:complications / Q000000981:diagnostic imaging* / Q000601:surgery; D012785:Shoulder Joint / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
keywords: 3D reconstruction; CT scan; Humeral head subluxation; glenoid version; total shoulder arthroplasty