A method for determining the mechanical characteristics of orthotic knee joints

All orthotic equipment must operate at the highest possible standards of safety and, should structural failure of a loaded component occur, there must be a minimal possibility of injury to the user. Because of the lack of definitive data on the in-service loading of lower limb orthoses it is not possible to base a test procedure on "real" loading conditions. In this paper a method of destructive testing, based on the assumption that the predominant loading consists of bending about the medio-lateral and anterior-posterior axes, is described. This method makes it possible to measure the bending strength of a knee joint side member assembly and to define the brittleness of the failure. It is suggested that the latter definition makes it possible to predict the potential safety of a particular knee joint should in-service failure occur. Some laboratory failures are described and recommendations, based on the test programme, are made for new joint designs.