Abstract
The fit of a lower limb prosthetic socket is critical for user comfort and the quality of life of lower limb amputees. Sockets are conventionally produced using hand-crafted patient-based casting techniques. Modern digital techniques offer a host of advantages to the process and ultimately lead to improving the lives of amputees. However, commercially available scanning equipment required is often expensive and proprietary. Smartphone photogrammetry could offer a low cost alternative, but there is no widely accepted imaging technique for prosthetic socket digitisation. Therefore, this paper aims to determine an optimal imaging technique for whole socket photogrammetry and evaluate the resultant scan measurement accuracy. A 3D printed transtibial socket was produced to create digital and physical twins, as reference models. The printed socket was photographed from 360 positions and simplified genetic algorithms were used to design a series of experiments, whereby a collection of photos were processed using Autodesk ReCap. The most fit technique was used to assess accuracy. The accuracy of the socket wall volume, surface area and height were 61.63%, 99.61% and 99.90%, respectively, when compared to the digital reference model. The scanned model had a wall thickness ranging from 2.075 mm at the top to 7.758 mm towards the base of the socket, compared to a consistent thickness of 2.025 mm in the control model. The technique selected did not show sufficient accuracy for clinical application due to the degradation of accuracy nearer to the base of the socket interior. However, using an internal wall thickness estimation, scans may be of sufficient accuracy for clinical use; assuming a uniform wall thickness.
Highlights
Obtaining a reliable and comfortable socket fit remains one of the largest areas of dissatisfaction amongst lower limb amputees [1,2,3]
An existing transtibial socket was marked with pattered tape allowing for easier identification of overlap within images by the photogrammetry software
This paper presents a low-cost smartphone photogrammetry technique for scanning entire prosthetic sockets
Summary
Obtaining a reliable and comfortable socket fit remains one of the largest areas of dissatisfaction amongst lower limb amputees [1,2,3]. Transtibial sockets are produced from handmade plaster casts of an individual’s residual limbs, these casts are manipulated to produce a rectified copy of the original patient’s limb. The rectified cast is subsequently used as a mould to form the socket material [4,5,6,7]. When the socket fit changes the socket is discarded and a new socket is produced. This is often a lengthy and wasteful process, especially if only minor revisions are needed. Digital technologies can replace stages in the traditional socket manufacturing process, such as rectification, mould production, and final socket fabrication. Digital techniques offer a host of advantages over conventional techniques, such as reproducibility, design history, and rapid prototyping
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