Comparison of measurements of the glenopolar angle in 3D CT reconstructions of the scapula and 2D plain radiographic views.
OBJECTIVE
The aim of this study was to analyse the effect of altered viewing perspectives on the measurement of the glenopolar angle (GPA) and the differences between these measurements made on 3D CT reconstructions and anteroposterior (AP) scapular view radiographs.


METHODS
The influence of the viewing perspective on the GPA was assessed, as were the differences in the measurements of the GPA between 3D CT reconstructions and AP scapular view radiographs in 68 cadaveric scapulae.


RESULTS
The median GPA in 3D reconstructions and AP scapular views were 42.7° (95% confidence intervals (CI), 42.0° to 43.5°) and 41.3° (95% CI 40.4° to 42.0°) respectively (p < 0.001). All but five of 20 malpositions demonstrated a significant difference in GPA compared with the respective AP scapular view (p ≤ 0.005). The GPA was most susceptible to malposition in retroversion/anteversion. Inter- and intra-observer reliability for all measurements of the GPA was excellent for 3D CT reconstructions (intraclass correlation (ICC) 0.93 (95% CI 0.87 to 0.96) and 0.94 (95% CI 0.89 to 0.97), respectively) and higher than on AP scapular radiographs (p < 0.001). The intra- and inter-observer reliability was excellent in AP scapular views and malpositions in extension/flexion (ICC ≥ 0.84) but tended to decrease with increasing viewing angle in retroversion/anteversion.


CONCLUSIONS
These data suggest that 3D reconstructions are more reproducible than AP scapular radiographs in the assessment of the GPA and should be used to compare data in different studies, to predict outcome, define malunion, and act as an indication for surgery in patients with a scapular fracture. Cite this article: Bone Joint J 2016;98-B:1510-16.
University of Utah, Department of Orthopaedics, Orthopaedic Research Laboratory, 590 Wakara Way, Rm A0100, Salt Lake City, UT 84108, USA.
T
T
Suter
University of Utah, Department of Orthopaedics, Orthopaedic Research Laboratory, 590 Wakara Way, Rm A0100, Salt Lake City, UT 84108, USA.
H B
HB
Henninger
University of Utah, Division of Epidemiology, Department of Internal Medicine, 295 Chipeta Way, Salt Lake City, UT 84108, USA.
Y
Y
Zhang
University of Utah, Department of Orthopaedics, 590 Wakara Way, Rm A0100, Salt Lake City, UT 84108, USA.
J D
JD
Wylie
University of Utah, Department of Orthopaedics, 590 Wakara Way, Rm A0100, Salt Lake City, UT 84108, USA.
R Z
RZ
Tashjian
D000328:Adult; D000368:Aged; D002102:Cadaver; D005260:Female; D061165:Glenoid Cavity / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011859:Radiography / Q000379:methods; D015203:Reproducibility of Results; D012540:Scapula / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods
Computed tomography; Glenopolar angle; Radiograph; Shoulder