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Perfect Fit: Using 3D technologies to manufacture custom prosthetic arm sockets

Emelie Strömshed, a masters student in product development at the School of Engineering at Lund University in Sweden, has developed a step-by-step process to combine prosthetic arm socket CAD data with 3D scan data of a patients residual limbs to create perfectly fitting 3D printed prosthetics arm sockets.

Under the supervision of Christian Veraeus, prosthetist and at Aktiv Ortopedteknik, and Prof. Olaf Diegel, professor of product development at Lund University, Emelie undertook a comprehensive study of the possibilities of using 3D technologies, including 3D CAD, 3D scanning, and 3D printing, to produce prosthetic sockets that better fit the clients, and were more efficient to produce. The process Emelie developed is intended to function as a guide for a prosthetist without requiring an extensive experience in CAD. The project aims to offer a viable alternative to the often time-consuming and manual labour-intensive conventional manufacturing method, as well as to provide amputee patients with perfectly fitted prosthetic sockets. A time and cost comparison was also performed and showed time savings of 400h/year and cost reductions of up to 261,000SEK/year through using the new process.

Neya Pfannenstill wearing the custom prosthetic arm socket and passive prosthetic arm developed by Emelie.

The current process of creating prosthetic arm socket molds that can then be used to create custom sockets.

The traditional method of manufacturing prosthetic sockets is a very manual crafting techniques that is as much an art as a science, and requires skilled craftsmen to do properly. The process involves the use of a plaster cast to create a negative mold of the residual limb, which can then be used to create a positive cast of the residual limb. The plaster limb is then manually modified and used to thermo-form a prosthetic socket, or the mold is laminated with plastic resin which can be reinforced with fiber-glass or carbon fiber. Sometimes a silicone interface is also added to increase the comfort of the prosthetic. One of the objectives of this project was to produce an easy-to-follow process, using low-cost 3D scanning technologies, that allowed normal prosthetic technicians to produce a perfectly fitting prosthetic socket without requiring advanced CAD skills.

Emelie's process involved the use of a low-cost iSense 3D scanning accessory that transforms your iPad into a 3D scanner. The prosthetic socket is created directly from the 3D scan data of the residual limb by offsetting the limb surface a distance equal to the desired thickness of the socket followed by subtracting the original 3D scan (no other CAD-model required) leaving an inner surface that perfectly fits the user. The process allows for the socket to be adapted to the use of both passive and active myoelectric prostheses. In the pictures of Neya, the socket has been integrated with a passive prosthesis that was created using an existing surface model of an arm that was imported, decorated and adjusted in the software according to the wearer's anatomy. Future versions of the process could, for example, allow the prosthetic to easily be decorated by the user to suit their own preferences. The final model is then sent to a selective sintering system, one of the common industrial 3D printing technologies that is capable of producing very strong nylon parts, and the prosthetic is produced, usually within a few hours. The final part can then be coloured if desired.

Neya Pfannenstill at play with her new custom prosthetic socket and arm.



copyright 2011, olaf diegel