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.

Digitising prosthetic sockets and moulds is critical for advanced fabrication techniques enabling reduced lead times, advanced computer modelling, and personalised design history. Current 3D scanners are expensive (>GBP 5000) and difficult to use, restricting their use by prosthetists. In this paper, we explore the use and accuracy of smartphone photogrammetry (<GBP 1000) as an accessible means of digitising rectified socket moulds. A reversed digital twin method was used for evaluating accuracy, in addition to simplified genetic algorithms to identify an optimal technique. The identified method achieved an accuracy of 99.65% and 99.13% for surface area and volume, respectively, with an interclass coefficient of 0.81. The method presented is simple, requiring less than ten minutes to capture using twenty-six photos. However, image processing time can take hours, depending on the software used. This method falls within clinical limits for accuracy, requires minimal training, and is non-destructive; thus, it can be integrated into existing workflows. This technique could bridge the gap between digital and physical workflows, helping to revolutionise the prosthetics fitting process and supporting the inclusion of additive manufactured sockets.

Assessment of coupling between transtibial sockets and users is historically based on clinicians' observations and experience, but can be inaccurate and unreliable. Therefore, we present a proof of concept, for five out of six possible degrees of freedom coupling metric system for a socket, using motion analysis calibrated on a 3D printed limb substitute. The method is compatible with any socket suspension method and does not require prior modifications to the socket. Calibration trials were used to locate the axis of rotation of the knee joint referenced against a marker cluster on the thigh; this allowed for the identification of the limb during test trials despite the entire residuum being obscured from view by the socket. The error in the technique was found to be within 0.7mm in displacement and 0.7 degrees in rotation, based on the control data. Dynamic testing showed the Inter Quartile Range (IQR) of inter time step variance was <0.5mm/deg for all metrics. The method can form a basis for objective socket evaluation, improve clinical practice and the quality of life for amputees.

Capturing limb shape for amputees is critical in the fabrication and delivery of comfortable prosthetic limbs. Smartphone Photogrammetry offers a cheaper and more accessible alternative to digital shape capture than traditional handheld 3D scanners, opening possibilities for remote, or in home scanning. In this study we aimed to evaluate the accuracy of smartphone photogrammetry using a technique designed for in home scanning, comparing performance to an Einscan H2. The results indicated that photogrammetry was suitable accurate for scanning static limb targets (>95% volumetric accuracy), but was not accurate enough for direct amputee scanning (63.4% larger volumes). Whilst this technique was not sufficiently accurate for clinical use, the amputee surrogate trials did show increased accuracy, indicating the method shows promise and should be developed further, with a particular focus on home environment compatible techniques.

Background: Assessing the fit and suitability of lower limb prosthetics is heavily reliant upon clinician observation and subjective feedback, often resulting in negative impacts on the comfort and quality of life of amputees. This is particularly important in the early stages of new socket fitment. Objective: This paper aims to use optoelectronic motion capture to measure the 5 degree of freedom coupling effectiveness of a newly fitted prosthetic limb during the adjustment period (6 weeks) of an active transtibial amputee. Methods: A 2-part calibration and trial data collection system was employed using Qualisys 3D motion capture, to track the relative position of limb and socket during walking trials. A single active transtibial amputee (27 male) was fitted with a new prosthetic socket and attended weekly data capture sessions using their prosthesis normally. Results: Here, we present evidence for alteration in prosthesis-residuum coupling performance, notably, the average proximal/distal displacement (pistoning) increased from 3.36 to 10.60 mm at week 6 from the first fit, which further increased to 12.90 mm with the use of a single prosthetic sock. Participant reported Socket Comfort Score reduced from 9 to 7 during this time. Conclusions: This pilot study provides new insight into the dynamic behavior of prosthetic sockets and could form the basis for larger studies determining a framework for safe and comfortable coupling limits.