Estimation of contact forces between lower limb and orthosis during gait is useful to prevent skin issues in subjects wearing this type of assistive devices. While inverse-dynamics based gait analysis of multibody models is difficult to apply due to the limited accuracy of motion capture systems, a forward-dynamics based analysis in which leg and orthosis are considered as independent entities is shown to provide acceptable results. Contact model parameters are calibrated through comparison of measured and calculated bending torque at the orthosis location where a load cell is installed, and the attained correlation allows to validate the model.