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1. Introduction
The “quality” of the socket fit, providing the coupling between the skeleton of the residual limb and the rigid structure of the prosthesis, is vital to the overall success of the prosthetic replacement. This quality is the most important characteristic of lower limb prostheses as indicated by prosthetic users [1–3].
State of the art prosthetic sockets is designed and handcrafted individually. The socket is usually made through the process of shape capturing, rectification, and alignment. Depending on the socket concept, a Plaster of Paris (POP) wrap cast is manually applied over the residual limb (residuum) or over the elastomeric liner covering the residual limb with the aim to capture a modified shape of the soft tissues. This shape is used to produce a positive model, which is afterwards adapted (rectified) according to one of a number of design paradigms. These procedures are highly individual, often inconsistent, and based on tacit knowledge. The performance by an individual prosthetist will be strongly influenced by personal experience, skill, and beliefs [4, 5]. When the socket design process is not reproducible, it will, besides the obvious prosthetic fit issues, affect the positioning of the socket relative to the prosthetic foot (alignment) and hence alter ambulation. Without doubt, those difficulties compromise the prosthetic rehabilitation process [4–6].
The evaluation of the shape capturing process and subsequent rectification process in terms of repeatability of inter- and intrasocket volume and shape comparison is notoriously complicated, due to the difficulty in establishing an accurate and reliable reference grid. It was reported that it is feasible to use the tibia bone, the only rigid entity of the residuum, as a reference grid for 3D alignment of multiple MRI images [7] and spiral X-ray computed tomography (SXCT) scans [8–10]. Both SXCT and MRI technologies are capable of providing two-dimensional (2D) and three-dimensional (3D), soft, and hard (bone) tissue images of the residual limb.
Additionally, 3D images from both systems have been used in the production of prosthetic sockets using computer-aided design and manufacturing (CAD-CAM) technology and finite element (FE) studies [11–17]. The CAD offers a way to do what prosthetists have been doing manually in a computerised way and, hence, could be considered having consistency due to the nature of the approach. The digital...