Design and Development of Mock Residual Limb Moulds: Towards the Development of Standard Tests for Transtibial Socket Structural Testing

Among the components of lower limb prosthesis, the socket is the most important, as it is the proximal part in direct contact with the patient's residual limb. Despite being the key element, there are currently no universal standards for evaluating the structural integrity of the sockets, hindering the implementation of new optimized fabrication processes. For this reason, the AOPA Socket Guidance Workgroup, an international community of experts, was established to propose socket structural testing guidelines to comply with recently enacted regulations. Specifically, for transtibial socket prostheses, knowledge gaps have emerged in four key domains: 1) Mock Residual Limb; 2) Coordinate System; 3) Test Specimens; and 4) Test Conditions. Given this premise, the aim of this thesis focuses on addressing the first gap. Specifically, starting from the three critical transtibial mock limb shapes identified by experts, parameterized moulds were designed for the fabrication of repeatable and reproducible mock residual limb to be integrated in the unified bench test setup. Initially, the documentation concerning the three selected critical mock limb shape (Long Cylindrical Bulky, Long Conical Slender and Short Cylindrical Bulky) and the three composition types (Rigid, Compliant and Hybrid) intended for the fabrication of the mock limbs, was analysed. The resulted considerations highlighted, first, the need to develop a specific bone surrogate for each shape, to be embedded within the Compliant-type surrogates in order to more realistically simulate the physiological condition of the transtibial residual limb. Subsequently, the Hybrid-type surrogates were modelled by applying scaling operations to the original versions of the shape models. Obtaining the solid models of the surrogates, the design phase was conducted in SolidWorks. A crucial step involved the definition of the software’s Reference System consistent with those of the mock limbs. In addition, since orientation was a key factor for successful testing, common components were designed to be analogously integrated across all moulds, enabling to known and maintain the position and orientation of the surrogates from the initial casting stage through bench assembly. Subsequently, using CAD operations, moulds were designed for each mock limb and its corresponding bone surrogate, following an iterative process aimed at optimizing volumes and reducing production time. At the INAIL Prosthetic Center, the last phase of the project was initiated, beginning the production of the first moulds using 3D printing technologies. The first versions of the fabricated parts enabled to evaluate and correct structural issued in several components, identify post-production challenges, which are currently under investigations, and formulate conclusions about potential improvements applicable across various steps of the process.