Effects of movement for estimating the hip joint centre.

Determination of the hip joint centre (HJC) using a functional approach requires access to the kinematics of various body postures. The present study aimed to determine the combined impact of the nature of the movement, its type and the number of cycles, on the accuracy of HJC estimation. Kinematics noise was modelled based on the deformation of hip and thigh clusters of seven subjects, while perfect ball-and-socket movements (used as reference) were calculated based on the movements of one of the subjects. The noise added to the reference kinematics allowed the simulation of 27 tests. Errors were defined as the Euclidean distance between the estimated and the reference HJC. A nested ANOVA and a multiple comparison procedures were performed on all errors. A test including 10 cycles of three different types of limited movements (flexion-extension, abduction-adduction and circumduction) yielded the greatest accuracy for estimating HJC (4.0+/-1.3 mm). Combining different types of movements allowed improving the accuracy. Given that noise increases as a function of the range of a motion, limited movements proved to be the most accurate; however, 10 cycles were required to achieve such results. For trials involving a single cycle, a large movement proved more efficient.