 Therefore, the aim of this study is to determine psychometric properties of the existing instruments in a large international data set, to explore possible linkage between self-reported and performance or observation-based instruments and to develop state-of-the art recommendationspoints to consider on how to assess functioning in prosthetic care. Projects exploring outcome assessments should have a broad basis and target different patient populations. To be able to generalize the outcome of the study for the European population, this study is planned as a multi-centre study. Also, having a sufficient number of subjects to calculate statistical relationships is otherwise not possible due the limited number of patients being treated at most centers. 