title: Estimating Glenoid Width for Instability-Related Bone Loss: A CT Evaluation of an MRI Formula.
abstract: BACKGROUND
  Determining the magnitude of glenoid bone loss in cases of shoulder instability is an important step in selecting the optimal reconstructive procedure. Recently, a formula has been proposed that estimates native glenoid width based on magnetic resonance imaging (MRI) measurements of height (1/3 × glenoid height + 15 mm). This technique, however, has not been validated for use with computed tomography (CT), which is often the preferred imaging modality to assess bone deficiencies.
  
  
  OBJECTIVE
  The purpose of this project was 2-fold: (1) to determine if the MRI-based formula that predicts glenoid width from height is valid with CT and (2) to determine if a more accurate regression can be resolved for use specifically with CT data.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Ninety normal shoulder CT scans with preserved osseous anatomy were drawn from an existing database and analyzed. Measurements of glenoid height and width were performed by 2 observers on reconstructed 3-dimensional models. After assessment of reliability, the data were correlated, and regression models were created for male and female shoulders. The accuracy of the MRI-based model's predictions was then compared with that of the CT-based models.
  
  
  RESULTS
  Intra- and interrater reliabilities were good to excellent for height and width, with intraclass correlation coefficients of 0.765 to 0.992. The height and width values had a strong correlation of 0.900 (P < .001). Regression analyses for male and female shoulders produced CT-specific formulas: for men, glenoid width = 2/3 × glenoid height + 5 mm; for women, glenoid width = 2/3 × glenoid height + 3 mm. Comparison of predictions from the MRI- and CT-specific formulas demonstrated good agreement (intraclass correlation coefficient = 0.818). The CT-specific formulas produced a root mean squared error of 1.2 mm, whereas application of the MRI-specific formula to CT images resulted in a root mean squared error of 1.5 mm.
  
  
  CONCLUSIONS
  Use of the MRI-based formula on CT scans to predict glenoid width produced estimates that were nearly as accurate as the CT-specific formulas. The CT-specific formulas, however, are more accurate at predicting native glenoid width when applied to CT data.
  
  
  CONCLUSIONS
  Imaging-specific (CT and MRI) formulas have been developed to estimate glenoid bone loss in patients with instability. The CT-specific formula can accurately predict native glenoid width, having an error of only 2.2% of average glenoid width.
authors.affiliation: Roth McFarlane Hand and Upper Limb Centre, London, Ontario, Canada Western University, London, Ontario, Canada Mechatronics in Medicine Laboratory, Department of Mechanical Engineering, Imperial College London, London, UK giles.joshgiles@gmail.com.
authors.forename: Joshua W
authors.initials: JW
authors.lastname: Giles
authors.affiliation: Keller Army Hospital, US Military Academy, West Point, New York, USA.
authors.forename: Brett D
authors.initials: BD
authors.lastname: Owens
authors.affiliation: Roth McFarlane Hand and Upper Limb Centre, London, Ontario, Canada Western University, London, Ontario, Canada.
authors.forename: George S
authors.initials: GS
authors.lastname: Athwal
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001862:Bone Resorption / Q000000981:diagnostic imaging / Q000473:pathology*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012540:Scapula / Q000000981:diagnostic imaging / Q000473:pathology; D012785:Shoulder Joint / Q000473:pathology*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
keywords: CT; MRI; bone loss; shoulder instability