The L5/S1 joint moment sensitivity to measurement errors in dynamic 3D multisegment lifting models

The purpose of this study was to compare the sensitivity of two dynamic tridimensional (3D) multisegment lifting models (upward and downward) to different errors. Two types of lifting tasks (sagittal and asymmetric) were considered. Five cameras, two force platforms and a dynamometric box provided inputs to the models. Known errors were induced in (1) joint centres, (2) the orientation of the anatomical coordinate system (ACS) of the pelvis, (3) external forces and (4) their point of application, (5) linear accelerations of segments' centre of mass and (6) body segment parameters (BSP) data to study their effect on the L5/S1 moments of both models. The results revealed that errors in joint centres and in the orientation of ACS axes were the principal sources of variability for both models. The upward model also require precise measurement of the point of application of the external forces while a downward model needs an accurate estimation of the BSP of trunk segments and an adequate estimation of upper segment accelerations. Since combined errors in the three moment components at L5/S1 generated an average of 5-9% incertitude in lumbar compression force estimates, it was concluded that the reduction of moment errors is important in spine modelling. (C) 1999 Elsevier Science B.V. All rights reserved.