Determining the optimal flexion-extension axis of the elbow in vivo - a study of interobserver and intraobserver reliability

In the current study the interobserver and intraobserver reliability of a r ecently developed method to obtain the position and orientation vectors of the flexion-extension axis of the elbow in vivo is determined. The method u ses the Flock of Birds(TM) six degrees-of-freedom electromagnetic tracking device. Ten subjects performed three trials comprising five flexion and ext ension cycles. The movements of the forearm with respect to the upper arm w ere recorded. Observer A measured two trials and observer B measured one tr ial. Optimal instantaneous helical axes were calculated in a humeral coordi nate system for each trial. Intraclass correlation coefficients and 99% con fidence intervals were computed to compare the three measurements. Zero was in the range of all the narrow confidence intervals, which is strong indic ation for resemblence. Interobserver intraclass correlation coefficients va lues for orientation vectors were good to excellent and intraobserver value s were fair to good. The intraclass correlation coefficients values for pos ition vectors were lower, probably due to the lack of variance between subj ects. It is concluded that the method is reliable and can be used in certai n clinical settings. (C) 2000 Elsevier Science Ltd. All rights reserved.