title: Accuracy of the glenohumeral subluxation index in nonpathologic shoulders.
abstract: BACKGROUND
  Correction of posterior humeral subluxation, measured by the humeral subluxation index (HSI) according to Walch, is necessary in total shoulder arthroplasty to prevent early loosening. The 3-dimensional (3D) measurement of the shoulder is becoming well accepted and common practice as it overcomes positional errors to which 2-dimensional (2D) glenohumeral measurements are prone. The first objective was to describe the HSI in a nonpathologic population with the 2D HSI according to Walch and a newly described 3D HSI method. The second objective was to compare both measuring methods with each other.
  
  
  METHODS
  In 151 nonpathologic shoulders, the 2D HSI was measured on the midaxial computed tomography scan cut of the scapula. The 3D HSI, based on the native glenoid plane, was defined as [formula in text], in which X is the projection of the center of the humeral head to the anteroposterior axis of the glenoid fossa and R is the radius of the humeral head. Both measuring methods were compared with each other. Correlation was determined. Interobserver and intraobserver reliability of the 3D HSI was measured.
  
  
  RESULTS
  The mean 3D HSI (51.5% ± 2.7%) was significantly (P < .001) more posterior than the mean 2D HSI (48.7% ± 5.2%), with a mean difference of 2.9% ± 5.6%. No correlation was found between the 2D and 3D HSI. The interobserver and intraobserver reliability was excellent.
  
  
  CONCLUSIONS
  The 2D HSI seems to underestimate the humeral subluxation compared with a 3D reliable equivalent.
authors.affiliation: Department of Orthopaedic Surgery, University Hospital Basel, Basel, Switzerland.
authors.forename: Matthijs
authors.initials: M
authors.lastname: Jacxsens
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Ghent University Hospital, Ghent, Belgium.
authors.forename: Alexander
authors.initials: A
authors.lastname: Van Tongel
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Ghent University Hospital, Ghent, Belgium.
authors.forename: Laurent B
authors.initials: LB
authors.lastname: Willemot
authors.affiliation: Department of Orthopaedic Surgery, University Hospital Basel, Basel, Switzerland.
authors.forename: Andreas M
authors.initials: AM
authors.lastname: Mueller
authors.affiliation: Department of Orthopaedic Surgery, University Hospital Basel, Basel, Switzerland.
authors.forename: Victor
authors.initials: V
authors.lastname: Valderrabano
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Ghent University Hospital, Ghent, Belgium. Electronic address: lieven.dewilde@uzgent.be.
authors.forename: Lieven
authors.initials: L
authors.lastname: De Wilde
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019643:Arthroplasty, Replacement; D061165:Glenoid Cavity / Q000000981:diagnostic imaging*; D006801:Humans; D058430:Humeral Head / Q000000981:diagnostic imaging*; D021621:Imaging, Three-Dimensional; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D012783:Shoulder Dislocation / Q000000981:diagnostic imaging* / Q000601:surgery; D012785:Shoulder Joint / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
keywords: 3D CT scan; 3D evaluation; 3D reconstruction; glenohumeral subluxation; humeral subluxation index; subluxation index