# Creating Soft Sockets and 3D Scans from Plaster Casts --- For more pictures of soft socket creation, [check out the gallery](https://hub.e-nable.org/u/kreeser1/gallery/custom-gallery/view?openGalleryId=84#.jpeg). For more pictures of creating and post-processing plaster casts, [check out the gallery](https://hub.e-nable.org/u/kreeser1/gallery/custom-gallery/view?openGalleryId=85#.jpeg). For more pictures of 3D scanning, [check out the gallery](https://hub.e-nable.org/u/kreeser1/gallery/custom-gallery/view?openGalleryId=86#.jpeg). --- During my time at [Lake Victoria Disability Centre](wiki:/u/kreeser1/wiki/Lake+Victoria+Disability+Centre "Lake Victoria Disability Centre") and [HVP-Gatagara](wiki:/u/kreeser1/wiki/HVP-Gatagara+and+ORTHOLAB%3A+An+Introduction "HVP-Gatagara and ORTHOLAB: An Introduction"), I had the opportunity to see and take part in the many steps involved in making traditional prosthetic devices. This article aims to give an overview of how plaster casts of residual limbs are produced, how traditional soft [sockets](https://en.wikipedia.org/wiki/Prosthesis#Socket) are made, and how through the use of 3D scanning technology, digital models of these casts and sockets are created. ### Creating a Plaster Cast The process of creating a [plaster cast](https://en.wikipedia.org/wiki/Plaster) begins with draping the patient with a plastic tarp to prevent plaster from getting onto their clothes, or onto unintended parts of their body. [Petroleum jelly](https://en.wikipedia.org/wiki/Petroleum_jelly) is applied lightly to the residual limb to aid in release of the cast after the plaster bandages have cured. In certain cases, the limb may need to be shaved to further aid in the release of the cast. The prepared limb is wrapped with water-soaked plaster bandages, often with a rubber tube or other piece of material (a piece of metal or plastic) against the skin to protect the limb when cutting the cured cast away from the body in a later step. During application of the water-soaked plaster bandages, the bandages are massaged against the residual limb to smooth any seams or ripples in the material and to conform the bandages to the residual limb as best as possible. The plaster is allowed to set, taking approximately 15-20 minutes. The negative casts are removed from the limb by carefully cutting down one side with a razor, following the underlying rubber tube or other piece of protective material, perpendicular to a series of horizontal lines drawn in skin-marking pencil. The horizontal lines are drawn for reference to ensure the seam of the cast can be closed and aligned properly later.  ###### Upper Left: Kyle Reeser wraps a patient’s torso and lap in a plastic drape. Upper Middle: Water-soaked plaster bandages are wrapped around the patient’s residual limb, with a piece of rubber tubing to cut along when removing the cast later. Upper Right: Kyle Reeser wraps a patient’s residual limb with water-soaked plaster bandages. Lower Left: Rajab Hamis wraps a water-soaked plaster bandage around the patient’s residual limb, with a piece of rubber tubing to cut along when removing the cast later. Lower Middle: Water-soaked plaster bandages are wrapped around the patient’s residual limb, with a piece of rubber tubing to cut along when removing the cast later. Lower Right: Cutting the cured plaster cast with a razor blade along the underlying rubber hose. --- Contours and measurements taken from the patient are sketched into the inside of the plaster cast with a skin-marking pencil, followed by skirting the cast with additional plaster bandage to make the rim of the opening even.  ###### Views of a negative plaster cast of a patient’s residual limb (left limb). Note the markings in skin-marking pencil (blue). --- Petroleum jelly is applied lightly to the inside of the negative cast, and a liquid plaster mixture is poured in. A metal rod is positioned within the cast, now serving as a mold, for ease of handling after the plaster positive cures and is removed from the mold. The plaster positive takes approximately 45-60 minutes to fully cure, and is removed by cutting away the negative mold that surrounded it.  ###### Views of a negative plaster cast being filled with liquid plaster and a metal rod, and allowed to set. The negative plaster cast ‘mold’ is later removed to reveal a positive plaster cast. --- The result is a positive cast that closely approximates the shape and dimensions of the patient’s residual limb. This positive cast requires significant post-processing before being used later in the process of creating a thermoformed soft socket.  ###### A positive plaster cast after removal from the negative plaster cast ‘mold’, with a tack indicating the height to which more plaster should be added along the bone. --- As foam material will later be thermoformed around the positive plaster cast to create a soft socket: 1. Adding material to the positive plaster cast will result in a larger void inside of the final soft socket, and 2. Removing material from the positive plaster cast will result in a smaller void in the final soft socket For a comfortable and proper lower limb soft socket fit, the soft socket should be be slightly tighter around soft tissue (muscle) and leave a little more room for bony areas of the residual limb. Small tacks are hammered into the positive cast along bone lines, and allowed to stick up from the cast 2-3 mm. These tacks act as guides and anchoring points for the addition of plaster material in these areas. Being faithful to the original shape of the limb, plaster is added to the cast to meet these tacks. Plaster to be added to the original positive cast is tinted a slight blue by adding [methylene blue](https://en.wikipedia.org/wiki/Methylene_blue). Due to this light blue tint, there is a blue-to-white transition at the boundary of the original plaster and the plaster added during post-processing. As rasps are used to remove material during shaping and processing of the cast, the technician knows when they have reached this layer that they are now removing original plaster. The final, processed positive plaster cast should be smooth and free from defects, with slightly-altered dimensions provide a more snug and comfortable fit.  ###### Plaster (tinted slightly blue with methylene blue) is added to the positive plaster cast in post-processing. --- ### Creating a Soft Socket Traditionally-made soft sockets at HVP-Gatagara were created from sheets of 6 mm thickness polyethylene foam. The post-processed positive plaster cast is used as a form for [thermoforming](https://en.wikipedia.org/wiki/Thermoforming) under vacuum, so a polyethylene foam tube is first fashioned with inner diameter just large enough to slip over the plaster cast. The technician measures the [proximal and distal](https://en.wikipedia.org/wiki/Anatomical_terms_of_location#Proximal_and_distal) diameters of the plaster cast and transfers these measurements (plus some percentage increase) to a sheet of polyethylene foam, tracing out a [trapezoidal](https://en.wikipedia.org/wiki/Trapezoid) shape. The technician uses a belt sander to trim the long edges of the foam trapezoid at an angle (as shown in the figure below) to increase the surface area for later bonding of those long ends with contact adhesive together to form a tube. HVP-Gatagara uses Premia Bond contact adhesive for this purpose, and I quote information from the Premia Bond packaging below: --- *Premia Bond contact adhesive, manufactured by: Dynamic Chemicals Ltd. (Nairobi) Suitable for bonding leather, rubber, plastic, floor tiles, ceramic, wood, Formica, glass, metal, and textiles* 1. *Ensure all surfaces to be bonded are free from grease \[and\] dust, and are dry.* 2. *Apply glue to both surfaces and let it dry for 8-10 minutes.* 3. *Bring the two surfaces together and apply pressure to ensure a firm bond.* 4. *With time, the bond between the surfaces will become stronger.* --- Roberto Postelmans took the “apply pressure to ensure a firm bond” direction a little further, by using a rubber mallet to pound the seam against a workbench for 30-45 seconds to maximize this bond.  ###### Upper Left: A P&O technician at HVP-Gatagara cuts out a trapezoidal shape that, when rolled into a tube, would be the approximate shape needed for a soft socket. Upper Middle: The technician uses a power sander to sand the long edges of the trapezoid at an angle. Upper Right: The technician applies contact adhesive to the long edges of the trapezoid and folds it into a tube. Lower Left: A diagram showing how the foam material is folded into a tube. Lower Right: Roberto Postelmans uses a rubber mallet to pound the seam of the foam tube to ensure strong adhesion at the seam. --- The positive plaster cast is held in place near the head of a specially-made vacuum head by inserting the metal rod of the cast into the large hold of the vacuum source (see figure below). The polyethylene foam tube is heated in an oven at 80 degrees Celsius for several minutes to soften the material. The hot, foam tube is quickly slid over the plaster cast, followed by a thick plastic bag. Vacuum is applied, sucking the air out of the bag and causing it to compress the foam tube against the underlying plaster cast. Vacuum is applied for approximately 1 minute as the foam returns to room temperature, with the interior of the foam tube now taking the shape of the positive plaster cast of the residual limb.  ###### Upper Left: Thermoforming of a soft socket under vacuum. Upper Right: The result or thermoforming, prior to being trimmer away. Lower Left and Lower Right: The blunt head of a vacuum system for thermoforming soft sockets. The blunt head has a large central hole through which the metal rod of the positive plaster cast can be inserted. The large and small holes of the blunt head provide vacuum. --- The thermoformed foam tube — hereafter referred to as the soft socket — is kept on the plaster cast for stability as it is post-processed. Material is easily subtracted from the soft socket by sanding the polyethylene form, and is easily added by gluing strips of the foam to itself using contact adhesive. In this way, a cap of foam is added to the distal side of the soft socket, sealing the otherwise open-end left from the original foam tube. With the interior of the soft socket complimenting the plaster cast (and therefore the patient’s residual limb) perfectly, the technician can add material to the exterior of the soft socket to achieve a good fit with the hard socket that it will eventually mater with.  ###### Roberto Postelmans modifying the exterior of a soft socket with the layered buildup of foam material. --- Once post-processing of the exterior of the soft socket is complete, the soft socket can be wrapped in PVC leather for aesthetics and as a washable external protective barrier. The PVC leather is glued to the exterior of the soft socket using the same Premia Bond contact adhesive.  ###### Roberto Postelmans wrapping a soft socket with PVC leather using contact adhesive. --- The resultant soft socket can then be tried on by the patient to ensure a snug and comfortable fit. Any complaints by the patient can be rectified by modifying the positive plaster cast and beginning the thermoforming and shaping process over again.  ###### Views of the completed soft socket, wrapped with PVC leather. Note the slit cut vertically into the side of the soft socket, as strain relief when the patient slips the socket on. --- ### 3D Scanning Plaster Casts and Soft Sockets Roberto Postelmans of ORTHOLAB uses a Sense [3D scanner](https://en.wikipedia.org/wiki/3D_scanning) paired with 3D Systems Sense software to scan both positive plaster casts, and traditionally-made soft sockets. In 3D scanning a positive plaster cast, a digital model is created that can be used to 3D print a soft socket in eLastic or Filaflex material. In 3D scanning a traditionally-made soft socket, a digital model is created that can be used to 3D print a hard socket.  ###### Left: A plaster cast of a patient’s residual limb. Scanning a plaster cast yields a digital model that can be used to 3D print a form-fitting soft socket. Right: A traditionally-manufactured soft socket, formed over the plaster cast from the left panel. Scanning a soft socket yields a digital model that can be used to 3D print a matching hard socket. --- Using the Sense 3D Scanner software is relatively straight-forward (though the software was in French at ORTHOLAB, so there was a slight learning curve for me), and is described in detail elsewhere. In brief, when the start button is clicked, the scanner focuses on what is in front of it and highlights it in green. As the scanner moves relative to the object being scanned, the scanning software keeps track of it and starts generating a 3D digital mesh of the scanned object. The scanning software must always be able to recognize the object on the screen as a slightly altered view of the previous image it took of the object, i.e., it must see a continuity between views of the object in order to successfully map its exterior. Very often, the software will lose track of the object, and the process will need to be started again. There is a balance between moving slowly enough during scanning for the software to recognize this continuity between views, and quickly enough to avoid excessively-large files. For the duration of the scan, the software is continuously collecting data, and many times while we scanned in the ORTHOLAB, the computer froze due to excessively-large file sizes that needed to be processed into a final mesh.  ###### Isaac Rukundo, director of the P&O department at HVP-Gatagara, 3D scanning a plaster cast of a patient’s residual limb. --- Once a digital model of the positive plaster cast is created with the 3D scanner, the model can be processed in Blender (or other 3D modeling software) to correct imperfections from the scanning process. A model for a soft socket is created by generating a wire frame mesh around the model of the cast, followed by giving that wire frame some thickness and then deleting the model of the cast. The same process can be used to create a model for a hard socket from the soft socket scan. ### Notes on 3D Scanning I learned several tips during my time using the Sense 3D scanner at ORTHOLAB: * The process works best if the object to be scanned is stationary, and the 3D scanner is rotated around the object. We believe that the software works better then the background that the scanner sees is changing so it can be successfully cancelled out as the object mesh is formed. * In rotating the scanner around the object, the object should be kept centered in the scanner’s field off view, and the scanner should be held equidistant from the object at all times. * The scanner has great difficulty creating a proper mesh of a scanned hand. The times during the scanning process where the scanner cannot see the spaces between fingers leads to a pseudo-webbing between the fingers that must be digitally removed later in a 3D modeling program such as [Blender](https://en.wikipedia.org/wiki/Blender_(software)), a very time-consuming process.  ###### Left: Roberto Postelmans using a Sense 3D scanner to scan Kyle Reeser’s hand. Right: A 3D model resulting from scanning a hand. Note the material in between the fingers of the 3D scan, a deficiency in the 3D scanner’s ability to create an accurate model to track it’s registration points on the fingers. --- ### Takeaways The processes of creating high-quality plaster casts and soft sockets requires a highly sophisticated skill set and knowledge of both human anatomy and all manner of surgical techniques used in amputation. The manufacture of sockets — especially those for weight-bearing prosthetics — is never one-size-fits-all, and mistakes can lead to harm or disfigurement in the recipient. Weight-bearing prosthetic devices should never be deployed without the oversight of a trained P&O professional. With that said, general knowledge of these processes by members of the e-NABLE community can and will contribute to better devices of higher caliber. I found the idea of scanning the positive plaster cast to make a 3D printable soft socket model, and scanning the traditionally-made soft socket to make a 3D printable hard socket model, very useful and interesting. Often, I find myself thinking about 3D printing as black-and-white; either everything is 3D printed or nothing is 3D printed. It is encouraging to see Roberto utilizing 3D printing as a supplement to traditional P&O techniques, and not a replacement. The idea that perhaps a 3D printed soft socket could be prepared with a traditionally-constructed hard socket, or vise versa, is intriguing. ### e-NABLE Community Calls to Action The e-NABLE community is uniquely positioned to act as a distributed processing and manufacturing ‘army’ for humanitarian P&O professionals on the ground in countries of need. There are members of this global community who are experts in 3D modeling who could work with such humanitarian P&O professionals to process 3D scans. There are other members of the e-NABLE community who are 3D printing experts, able to produce very high-quality 3D printed soft, and hard, sockets from those processed scans. I would like to see members of the e-NABLE community self-identify certain skill sets that can be called upon in this way. If we establish ongoing working relationships with ORTHOLAB and Lake Victoria Disability Centre, It would be nice to be able to send requests to groups of members with specific skill sets who may be interested in helping with concrete humanitarian work.