The Use of Smartphone Photogrammetry to Digitise Transtibial Sockets: Optimisation of Method and Quantitative Evaluation of Suitability

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.

A Simple Way to Reduce 3D Model Deformation in Smartphone Photogrammetry

“…The second most popular field is medical applications. Solutions that allow recreating the shape and size of individual parts of the body [ 45 , 46 , 47 , 57 , 58 ] and models for the needs of, e.g., prostheses or plastic surgeries [ 48 , 49 , 51 , 63 ] are predominant here. In the case of geological issues, the analysis of rock porosity and roughness is a common topic [ 65 , 66 ], while in geomorphology it is popular to create digital models of various types of geomorphological forms (e.g., cliffs, caves) [ 70 , 71 ].…”

Phone cam array – An open-source, modular photogrammetry system made of Android phones

“…Cullen et al described the possibility of digitizing transtibial sockets [8] . The fit of a prosthesis is crucial for the lower limb amputees’ quality of life.…”

Methodology to Evaluate the Performance of Portable Photogrammetry for Large-Volume Metrology

“…Some software used to generate 3D models from images suggests positions for the following image [23,24]; this can also be achieved via a network of camera positions [25] which considers the shape of the workpiece being measured. However, these software tools are designed to obtain a mesh from matching points, and the accuracy is one order of magnitude less than when targets are used [9].…”