# A Design for a 3-Piece Transradial Socket and Cosmetic Hand --- Roberto Postelmans, founder of [Humanitarian Prosthetists and Orthotists](https://fr.hpo-lab.org/) (HP&O), directs ORTHOLABs in [Rwanda](https://en.wikipedia.org/wiki/Rwanda), [Burkina Faso](https://en.wikipedia.org/wiki/Burkina_Faso), [Togo](https://en.wikipedia.org/wiki/Togo), and [Benin](https://en.wikipedia.org/wiki/Benin). He works tirelessly, tucked away from most other humanitarian prosthetics organizations, sequestered geographically and linguistically. In effect, he is the Australia of the low-cost prosthetic device world. His prosthetics, like the marsupials, the result of years of isolated evolution. During my time working under Roberto at ORTHOLAB in [Gatagara](https://en.wikipedia.org/wiki/Nyanza,_Rwanda), Rwanda, I was impressed by a design for a 3D printed 3-piece transradial prosthetic device. The device consisted of the following three parts: 1. A custom 3D printed soft socket, the designs for which are the result of a 3D scan of a plaster cast taken of the patient’s residual limb 2. A 3D printed hard distal cap for the socket, acting as an attachment point for a cosmetic hand (or another end effector) 3. A cosmetic hand, prosthetic device, or another end effector  ###### Three-piece socket and cosmetic hand --- ### Soft Socket  ###### Views of the soft socket. The red arrows indicate location of raised mounds which help to keep the socket in place on the residual limb. --- The soft socket was designed specifically for one of our adult patients, based on a 3D scan of a plaster cast taken from her residual limb. The socket was printed with eLastic 3D filament (Natural) by [eSun](http://www.esun3d.net/). The socket was designed with several features: a) The socket was open at the proximal end but enclosed at the distal end, with the exception of an approximately 25 mm diameter hole, as seen below. The purpose of the hole was two-fold: I. For use with a fabric sleeve to slide the soft socket onto the residual limb, as in the figure below. Often a socket fits the residual limb so well that when trying to insert the residual limb, the skin and tissue can move with the tight-fitting socket making it difficult to place the socket in its proper position. First, the fabric sleeve is pulled over the residual limb with several centimeters of excess fabric on either side. The excess fabric sleeve at the distal end is guided out of the hole as the sleeved stump is inserted into the soft socket. The fabric sleeve is pulled taut as the socket is pushed into position. The excess sleeve material can either be pulled back over the distal end of the soft socket, or pushed pack inside of the socket through the hole.  ###### A fabric sleeve is used in conjunction with the hole in the socket --- II. The hole allows air to escape at the distal end of the socket as the limb is inserted. Once the limb is fully inserted, a rubber or 3D printed (eLastic) plug can be used to seal the hole, creating a vacuum that will better hold the prosthetic in position. b) The soft socket featured a triangular protrusion which mated with a hole in the phalanges of the hard distal cap, securing the cap in place. The protrusion was vaguely nose-shaped, allowing the distal socket phalanges to slide over it. After being locked into its mating hole in the distal socket phalange, it would be held in place until the protrusion was pressed inward to release it from the hole. This design feature worked very well given that the protrusion was made of deformable eLastic.  ###### The soft socket being inserted into the distal cap --- c) The interior of the soft socket was modeled from the 3D scan of the plaster cast, matching the patient’s residual limb. Raised mounds (red arrows) were added on the interior of the soft socket to lock the top and bottom of the distal stump into place. ### Distal Cap  ###### Views of the distal cap --- The primary function of the distal cap was to provide a solid connection between the soft socket and the cosmetic hand. The rounded end of the soft socket mates with the cavity in the distal cap, while the phalanges lock the distal cap into position over the soft socket. Roberto explained that these discrete phalanges allow the distal cap to rotate with the movement of the patient’s forearm in a way that a fully-circumferential device would not allow. The distal end of the distal cap was flat, meant to serve as a surface to which a cosmetic hand could later mate. A standard bolt can be inserted through the distal cap such that the threaded end of the bolt protrudes out of the distal end of the distal cap; hardware which can be used to secure the cosmetic hand (or additional effector). Finally, the overall shape of the exterior of the distal cap was designed to contour the prosthetic toward the approximate size and shape of the patient’s wrist.  ###### The assembled socket prior to attachment of the cosmetic hand --- ### Cosmetic Hand  ###### Views of the cosmetic hand --- The design for the cosmetic hand is one that Roberto already had, and has used for previous patients. He has a repository of several hand designs, both male and female, which he scales to a size appropriate for a particular patient. The cosmetic hand is printed in eLastic 3D filament (Natural) by eSun, the same material as the soft socket, while the fingernails are printed separately in PLA+ (Red) by eSun, and later glued into place. While not pictured, the back of each nail had a raised feature which mated with a hole on each finger where the nails would be placed. This allows the nailed to be positioned correctly and offers a stronger connection. The flat proximal end of the hand mates with the flat surface of the distal cap. The hand is screwed into position, with the bolt protruding from the distal cap being screwed into a hole in the proximal end of the hand. For a secure fit, a threaded insert should be added into this hole as the hand is printing. ### Takeaways During my time at ORTHOLAB, we focused primarily on cosmesis for the upper limb devices we created. However, different terminal devices could easily be paired with this socket system, ex. a gripper thumb or moto gripper. The plug used to seal the circular hole at the distal end of the soft socket could be replaced with a 3D printed valve, if such a design exists. Finally, I was sincerely impressed with how the eLastic cosmetic hand looked and felt. The hand could be slightly compressed making it feel more natural. The cosmesis could be dropped on the floor without fear of the fingers breaking off—it was very durable. The eLastic material offered a bit of grip, allowing it to serve basic functions such as sliding papers across a desk. Finally, using the eLastic ‘natural’ color (white) allowed for the device to be painted using Ottobock Superskin ([I’ll expand on this in another post](wiki:/u/kreeser1/wiki/Notes+on+Life+in+East+Africa+and+Tips+for+Future+Missions "Notes on Life in East Africa and Tips for Future Missions")). I believe e-NABLE and future recipients would benefit greatly from creating a repository of cosmetic designs, and eLastic should be used for soft sockets and cosmetic hands. Said more straightforwardly, there is a large population around the world that do not respond positively to the non-natural look of many of e-NABLE’s designs. Building up a repository of the 3D scanned hands of men, women, and children will offer us the ability to provide cosmetic designs to many potential recipients. ### e-NABLE Community Call to Action While I was given permission to share what I learned at ORTHOLAB, with the understanding and hope that the greater e-NABLE community would benefit from this design knowledge, ORTHOLAB stopped short of providing me with the CAD files for the 3-piece transradial cosmesis. A proof-of-concept version of this device should not be very difficult for members of the community skilled in CAD modeling to reproduce. If anyone is looking for a project, please consider designing an e-NABLE version of this design and contact me if I can answer any questions that would help faithfully reproduce the design.