Towards Modernising Trans-radial Prosthetic Socket Creation With Digital Methods

Abstract

Current upper-limb prosthetics do not fulfil the needs and expectations of their users. As a result, device rejection and abandonment rates have remained consistently high for more than six decades, predominantly due to a lack of functionality. Many individuals with upper limb differences feel more functional without their devices. This is despite significant advances in the sophistication of available bionic hands. It is believed that this is due to a lack of advancement in upper-limb sockets, the component that connects the device to the user’s body and enables device control. This topic has received relatively little study to date. The socket designs used in clinics today predate the invention of the majority of advanced bionics currently in use. Therefore, they are not designed to satisfy contemporary requirements. The main aims of this PhD thesis are to 1) identify the issues currently hindering progress in upper-limb prosthetics, 2) investigate novel manufacturing methods, for the benefits they could have, and 3) assess novel socket designs, to see if they could have any positive effect on the functionality and level of control that can be achieved with upper-limb prosthetic devices. Chapter 1 covers the motives and goals of this PhD thesis, as well as an outline of the subsequent chapters. Chapter 2, the literature review, includes a variety of fundamental subjects necessary for understanding the issues in the succeeding Chapters. An overview of relevant human anatomy, prevalent prosthetic limb styles, and the field’s present challenges is provided. Chapter 3 discusses the present state of prosthetic socket research. The Chapter is presented as a consensus of various specialists in the field, having experiences and viewpoints from both engineering research and clinical medicine. Current barriers and critical enablers of advancement within the field of prosthetic sockets are identified. Chapter 4 presents an overview of the general methods used throughout the PhD Thesis. Chapter 5 evaluates the feasibility of switching to contemporary socket manufacturing techniques that are typically believed to be capable of replicating the current clinical standard. Through a practical experiment,digitally made sockets were trialled with individuals with trans-radial limb di erence, and feedback was obtained. A key nding of this study is that clinical expertise must be incorporated into the socket manufacturing process, regardless of the method employed, in order to achieve consistently satisfactory results. Using a mixed digital-clinical approach,Chapter 6 builds on the ndings of Chapter 5 to create clinical standard upper-limb prosthetic socket simulators. The simulators were successfully built and enabled the recording of satisfactory EMG signals using a combination of digital scanning and traditional socket fabrication processes. Chapter 7 looks at how longitudinal compression a ects EMG control and localised muscle fatigue. The results of this Chapter show that longitudinal compression has no e ect on limb fatigue, but it may prevent loss of contact between the limb and the socket wall during contractions. Chapter 8 is the culmination of all knowledge acquired from the previous Chapters and presents a novel manufacturing method and design for a prosthetic socket simulator. The results show that combining mechanical perturbation of the limb with digital scanning can produce a reliable and useful outcome. The forearm cu s created from these scans indicate that high pressure, longitudinal compression socket styles may reduce electrode disturbances, but increase the risk of accidental co-contractions. Chapter 9 assesses the feasibility of implementing the methods and socket designs discussed in this thesis in clinics and makes recommendations on how this could be achieved. An outlook on the future of upper-limb prosthetic sockets is provided, as well as recommendations on when and how modern methods and designs can be realistically implemented.