Comparison of measurements of the glenopolar angle in 3D CT reconstructions of the scapula and 2D plain radiographic views.

AIMS: 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. MATERIALS AND 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. CONCLUSION: 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.

A functional axis based upper extremity model and associated calibration procedures.

An upper extremity model focusing on an accurate and complete description of elbow motion is introduced. Both glenohumeral center of rotation and functional elbow axes are computed and used for anatomical coordinate descriptions. Model results match goniometric measures of the flexed elbow and test-retest analyses of six subjects were repeatable within 5 degrees for most measures. The elbow axis from 25 individuals was located about 12 mm distal and anterior to the midpoint of the transepicondylar axis, placing it aligned with the center of the trochlea. Carrying angle of the elbow was determined to be 11 degrees of abduction (valgus) with the arm extended.