Estimating glenoid width for instability-related bone loss: A CT evaluation of an MRI formula

© 2014 The Author(s). 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 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. Purpose: 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. Study Design: 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\u27s 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\u3c.001). Regression analyses for male and female shoulders produced CT-specific formulas: for men, glenoid width = 2/3 3 glenoid height + 5 mm; for women, glenoid width = 2/3 3 glenoid height 1 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. Conclusion: 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. Clinical Relevance: 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

Intra-observer and interobserver reliability of the 'Pico' computed tomography method for quantification of glenoid bone defect in anterior shoulder instability

Objective To evaluate the intra-observer and interobserver reliability of the \u2018Pico\u2019 computed tomography (CT) method of quantifying glenoid bone defects in anterior glenohumeral instability. Materials and methods Forty patients with unilateral anterior shoulder instability underwent CT scanning of both shoulders. Images were processed in multiplanar reconstruction (MPR) to provide an en face view of the glenoid. In accordance with the Pico method, a circle was drawn on the inferior part of the healthy glenoid and transferred to the injured glenoid. The surface of the missing part of the circle was measured, and the size of the glenoid bone defect was expressed as a percentage of the entire circle. Each measurement was performed three times by one observer and once by a second observer. Intra-observer and interobserver reliability were analyzed using intraclass correlation coefficients (ICCs), 95% confidence intervals (CIs), and standard errors of measurement (SEMs). Results Analysis of intra-observer reliability showed ICC values of 0.94 (95% CI=0.89\u20130.96; SEM=1.1%) for single measurement, and 0.98 (95% CI=0.96\u20130.99; SEM=1.0%) for average measurement. Analysis of interobserver reliability showed ICC values of 0.90 (95% CI=0.82\u20130.95; SEM=1.0%) for single measurement, and 0.95 (95% CI= 0.90\u20130.97; SEM=1.0%) for average measurement. Conclusion Measurement of glenoid bone defect in anterior shoulder instability can be assessed with the Pico method, based on en face images of the glenoid processed in MPR, with a very good intra-observer and interobserver reliability