VALIDATION OF A LOWER-LIMB MODEL WITH IN-VIVO FEMORAL FORCES TELEMETERED FROM 2 SUBJECTS

A mathematical model of the human pelvis-leg system in the sagittal pl ane, with an anatomical model of the knee, was developed to calculate forces transmitted by the structural elements of the system. The model was used to study the influence of activity of hip flexors and extens ors on the forces in the femur during isometric exercises and during l evel walking. Kinematic and kinetic data together with simultaneous el ectromyography (EMG) and in vivo axial forces transmitted along the pr ostheses from two patients implanted with instrumented massive proxima l femoral prostheses were obtained. Comparison of the levels of the ca lculated axial forces in the model femur to the simultaneous telemeter ed forces showed good agreement for isometric tests. Interaction betwe en the muscles and the bones during isometric tests was examined and b i-articular muscles were shown to play a major role in modulating forc es in bones. The study supports the hypothesis that muscles balance th e external limb moments, not only at joints but also along the limbs, decreasing the bending moments but increasing the axial compressive fo rces in bones. It is thus suggested that appropriate simulation of mus cle force is necessary in in vitro laboratory experiments and in theor etical studies of load transmission in bones. The sagittal plane model underestimates the value of the maximum axial force in the femur duri ng walking by about 30% but suggests that 70% was due to the action of the extensors or flexors. The results encourage further development o f a three-dimensional model with anatomical models of the joints to in clude coronal and transverse planes for the study of adductors and abd uctors. (C) 1998 Elsevier Science Ltd. All rights reserved.