The computer aided design of below-knee prosthetic sockets

The thesis begins with an introduction to the conventional socket design and fabrication procedure. A computer based system is documented which was developed at UCL to design below-knee prosthetic sockets. The first objective in the system's development was to provide an automated facility capable of taking surface measurements of a residual limb and manipulating these data to produce a socket shape using conventional design philosophy. To refine the system, design must ultimately aim to provide an appropriate socket shape which produces a predetermined load distribution at the limb/socket interface. This requires an improved fundamental understanding of socket loading. An engineering study is presented in which the finite element (FE) method is used to predict interface loads in standing. The main objectives of this work are to produce a ‘first generation' FE model which realistically represents the tissues of a loaded residual limb and then to use this model to discover the key parameters which determine interface loads. Initially, idealised geometry and assumed mechanical properties are used to study the effects in the FE models of interface friction, distal end loading and soft tissue thickness. Realistic geometric data are obtained experimentally from measurements of external residual limb shape and bones and mechanical properties of residual limb tissues are evaluated from a series of in vivo indentation tests. Further finite element models of socket loads are based upon these measured data. The idealised FE models indicate that the conditions of friction at the interface and distal end-bearing have more dramatic effects upon gross load distribution than limb geometry. Those models based upon measured geometry and properties showed that variations in the socket rectification and in the distribution of mechanical properties of tissues predominated over alignment effects with regard to static pressure distribution