# Three-Dimensional (3D) Model-Based Lower Limb Stump Automatic Orientation
## 1 Introduction
A commonly applied solution is a web-based program, Rapid Plaster (PVA Med, New York, NY, USA), developed for the design of prosthetic sockets allowing users to work with a 3D-model in a conventional browser and convert it using standard tools for working with 3D models, although again it lacks a component that could be used for the automated orientation in 3D space [17]. Current classification of socket types, their common advantages and limitations from multiple viewpoints, as well as an overview of the keynote parameters affecting the stump-socket interface and influencing the comfort and stability of the limb prostheses such as displacement, stress, volume and temperature fluctuations for different positioning and orientation scenarios are reviewed in [18]. A physically motivated reduced model of the dynamic interactions between the residual limb and the prosthetic socket proposed in [19] is capable of the quantitative assessment and simulation of the stress distribution for different variants of the socket orientation and positioning as well as its possible alterations depending on the corresponding variation in the friction coefficients. Another recent knowledge-based approach to the design and orientation of the lower limb prostheses with particular focus on the 3D modeling of the socket is based on the acquisition and formalization of the knowledge related to the prosthesis manufacturing process as well as the architecture of a dedicated knowledge-based engineering framework detailing the key design steps. A computer-aided module named socket modeling assistant (SMA) represents a virtual laboratory where the socket prototype is being created and positioned based on the digital model of a patient'sresidual limb. The SMA software acts as an interactive tool to guide and support the expert socket designer during each step from socket design to its positioning and orientation either in an automatic or in a semi-automatic fashion [20]. The authors of [21] focus on untangling the complexity of the transtibial prosthetic socket fit by selecting the keynote characteristics that guarantee its successful fitting as well as finding certain criteria for the optimized selection of the particular prosthetic socket type for different positioning and orientation scenarios. Based on the analysis of the activity levels and reported satisfaction of active persons, especially among younger persons mainly with a traumatic cause of amputation, they conclude that the total surface-bearing sockets generally outperform the patellar tendon-bearing sockets, as they can be better adjusted to the lower limb stump in order to withstand dynamic loads typically associated physical activity. Socket biomechanics, socket pressure measurement, friction-related phenomena and associated properties, with corresponding computational models describing the limb tissue responses to the external mechanical loads and other physical conditions for different socket positioning and orientation scenarios are the key focus of [22]. Further advancement of this research is associated with the embedded sensors enabling direct measurements of the physical stresses applied to the socket [23]. The results of this study indicate that the direction and the angle of rotation of the stump could be obtained by decoding the magnetic field signals obtained by magnetic sensors embedded into a prosthetic socket. This pilot study provides important guidelines for the development of a practical interface between the residual bone rotation and the prosthesis for control of prosthetic rotation. The conventional approach to the prosthetic socket orientation includes splitting the stump 3D-model into sections according to a discrete grid in the horizontal plane followed by obtaining the resulting dimensions from the cross-section perimeters. Accordingly, registration of the cross-section perimeters while the 3D model is positioned at the wrong angle to the horizontal plane leads to incorrect measurements.