Effect of different inertial parameter sets on joint moment calculation during stair ascending and descending

The reliability of internal joint moment calculation in gait analysis during daily living activities is fundamental for clinical decisions based on joint function. This calculation, obtained by means of the inverse dynamics, depends on several modelling factors, such as assumptions on the segments and on the relevant joints constituting the kinematic chain. In this study, the effect of five different sets of inertial parameters on three-dimensional calculation of lower limb joint moments was investigated during the stair ascending and descending of 10 young subjects. The lower limb was represented as a chain of three rigid segments: foot, shank and thigh. The inertial parameters sets were taken from the literature. The root mean square value over the step cycle of the difference between joint moments calculated at the lower limb with different inertial parameter sets expressed in percentage of their corresponding range was computed. The results showed small differences between ex vivo and in vivo data, between data from different populations and among different modality of inertial parameters acquisition. The root mean square value was negligible at the ankle and increased as moving proximally among the joints: the maximum was 21.8% in the internal/external rotation moment at the hip. In order to achieve accurate estimate of lower limb joint moments other factors should be investigated rather than optimal inertial parameter set.