Errors in measuring glenohumeral arthrokinematics with 2-dimensional fluoroscopy

Two-dimensional fluoroscopic imaging allows measurement of small magnitude humeral head translations that are prone to errors due to optical distortion, out-of-plane imaging, repeated manual identification of landmarks, and magnification. This article presents results from in vivo and in vitro fluoroscopy-based experiments that measure the errors and variability in estimating the humeral head translated position in true scapular plane and axillary views. The errors were expressed as bias and accuracy. The variability with repeated digitization was calculated using the intraclass correlation coefficient (ICC) and the standard error of measurement. Optical distortion caused underestimation of linear distances. The accuracy was 0.11 and 0.43 mm for in vitro and in vivo experiments, respectively, for optical distortion. The intrarater reliability was excellent for both views (ICC = .94 and .93), and interrater reliability was excellent (ICC = .95) for true scapular view but moderate (ICC = .74) for axillary views. The standard error of measurement ranged from 0.27 to 0.58 mm. The accuracy for the humeral head position in 10° out of true scapular plane images ranged from 0.80 to 0.87 mm. The current study quantifies the magnitude of error. The results suggest that suitable measures could be incorporated to minimize errors and variability for the measurement of glenohumeral parameters.