The scapular glenopolar angle: standard values and side differences.

OBJECTIVE

The aim of this study is to determine normal glenopolar angle (GPA) values on bone specimens of the scapula and compare them with various radiological views and CT examination.

MATERIALS AND METHODS

GPA values were measured on 100 mature, dry, non-paired scapulae, 20 pairs of dry scapulae, 50 AP radiographs of the shoulder, 50 Neer I views, 50 AP chest radiographs and 20 3D CT reconstructions of the scapula.

RESULTS

Measurements made on bone specimens of the scapula showed an average GPA value of 42.3°; the mean absolute side-to-side difference was on average 1.6°. The average GPA measured on 50 AP shoulder radiographs was 35.9°, on Neer I views 40.6° and AP chest radiographs 37.1°, with the mean absolute side-to-side difference on average 4.9°; on 3D CT the average GPA was 43.0° and the mean absolute side-to-side difference on average 1.4°.

CONCLUSION

GPA values depend on the method of measurement used. Measurements made on 3D CT reconstructions and Neer I views showed almost the same values as those measured on bone specimens. The values measured on AP shoulder views and AP chest radiographs were statistically significantly lower. Side-to-side variability (right and left) measured on 3D CT reconstructions was insignificant, and the obtained values corresponded to the values from bone specimens. Therefore, the best method to measure the GPA is a 3D CT reconstruction and an exact Neer I projection.