Validation of the greater trochanter method with radiographic measurements of frontal plane hip joint centers and knee mechanical axis angles and two other hip joint center methods.

Several motion capture methods exist for predicting hip joint centers (HJC). These methods include regression models, functional joints, and projections from greater trochanters. While regression and functional methods have been compared to imaging techniques, the TROCH method has not been previously validated. The purpose of this study was to compare frontal-plane HJCs and knee mechanical axis angles estimated using the greater trochanter method with a regression (Bell) and a functional method against those obtained using radiographs. Thirty-five participants underwent a long-standing anteroposterior radiograph, and performed static and functional motion capture trials. The Bell, functional, and trochanter HJCs were constructed to predict mechanical axes and compare HJC locations. One-way repeated measures ANOVAs were used to compare mechanical axes and HJC locations estimated by motion capture methods and measured using radiographs (p<0.05). All methods overestimated mechanical axes compared to radiographs (<2°), but were not different. Mediolateral HJC locations and inter-HJC widths were similar between methods; however, inter-HJC widths were underestimated (average 3.7%) compared to radiographs. The Bell HJC was more superior and anterior to both functional and trochanter methods. The trochanter HJC was more posterior to both methods. The Bell method outperformed the other methods in leg length predictions compared to radiographs. Although differences existed between methods, all frontal-plane HJC location differences were <1.7cm. This study validated the trochanter HJC prediction method mediolaterally and vertically (with small respective correction factors). Therefore, all HJC methods seem to be viable in predicting mechanical axes and frontal-plane HJC locations compared with radiographs.