We get many questions about how prosthetic limbs are made. Below, we explain some of the different aspects and types of prosthetic limbs and what materials are used for making prosthetics and what makes up each part.
How Are Prosthetic Limbs Made?
The prostheses (prosthetic limbs) that are delivered to our clients are made up of parts which can be grouped into three broad categories: Prosthetic Socket, Prosthetic Components, and Consumables.
The Prosthetic Socket is the upper part of the prosthesis which fits around your residual limb (AKA stump). This Socket is custom made onsite within the APC prosthetic workshop by our talented technicians. Below the socket are Prosthetic Components which include connective components (made of aluminium, stainless steel or titanium), prosthetic joints (such as prosthetic hips, knees, elbows and wrists), and prosthetic feet or prosthetic hands (also known as a terminal device). These Prosthetic Components are ordered from suppliers to meet each client’s specific requirements. Finally, consumables include items such as liners, knee sleeves, and socks which allow your prosthesis to comfortably hold on to your residual limb. These Consumables, like Prosthetic Components, are ordered specifically for each client, featuring materials such as silicone, TPE, rubber and much more.
Download our resources about how to care for your prosthesis and consumables. Or ask for our limb care guide at your nearest APC clinic.
Prosthetic Sockets
Diagnostic Socket Fabrication
The process of having a prosthetic socket made begins with your prosthetist taking a plaster cast of your residual limb. This is then filled with plaster to become a plaster copy of your residual limb (positive plaster cast) which can be used to make a Diagnostic Socket or a ‘check socket’. The primary aim of this clear plastic socket is to optimise the socket fit, refine the alignment, and ensure the prosthesis meets all necessary functional and comfort goals.
A diagnostic socket utilises materials which are suitable for a short-term trial period. These include thermoplastic sheets which are heat blistered and vacuum moulded onto the client’s positive plaster cast. Following this step, the socket is attached to a lamination anchor which provides the connection between the custom-manufactured prosthetic socket and the remaining prosthetic componentry. To ensure safety and security, the anchor is secured to the socket. This can be done in a variety of ways from wrapping it in a fibreglass bandage, laminating carbon fibre or fibreglass over it. Once this is achieved, the diagnostic socket is ready for trial!
Definitive Socket Fabrication
Once the prosthetic socket fit and alignment have been optimised, the diagnostic socket is ‘duplicated’ in an alignment jig creating an identical plaster mould whilst retaining the correct alignment of the connective componentry. Plaster or alginate is used in this step. If the shape of the socket allows it to be removed from the positive mould, the client can continue to wear their check socket whilst an APC manufactures their ‘definitive socket’.
The materials used in making definitive prosthetic limbs can vary. Factors include impact, weight of the user, activities that will be undertaken, method of suspension, socket design etc. Most definitive sockets will be made using at least two separate laminations, although some are made using a single lamination.
Some prosthetic socket designs will incorporate a compressible liner (typically made of a material called pelite), PET-G or a flexible plastic inner depending on what the prosthetist has deemed most suitable for the client. If your socket has one of these features, this is fabricated first on the inner most layer to the plaster cast. If not, the plaster cast will be first sealed with lacquer or similar (to prevent moisture leaving the plaster during the lamination).
Next an appropriate combination of materials including carbon fibre, fibreglass, stockinette, perlon and/or nyglass are layered over the cast, sealed under vacuum between PVA bags. Acrylic resin mixed with a hardener and sometimes a coloured pigment is then added. The resin penetrates the material fibres and solidifies the lay-up as the chemicals react, in a process called lamination. The initial lamination is focused on creating a strong, structured framework.
The lamination anchor (or adapter) is attached with bog in a similar process to diagnostic sockets but using the alignment transfer jig. The use of foam and putties allows for improved cosmesis and a smooth transition from the adapter to the socket. The second lamination utilises similar materials to the first, however, its focus instead shifts towards strength and security of the lamination anchor to the socket.
This layer can incorporate further coloured pigments or fabrics to personalise your prosthesis and show off your personality. We can laminate most materials as the final layer in the socket allowing endless cosmetic possibilities. Many clients opt for a specific design to finish their prosthetic sockets ranging from Indigenous Art to sports teams – there is such a variety! Clients are encouraged to bring in fabrics, t-shirts, or designs which they desire on their final socket. Sometimes a third clear layer of resin is needed to ensure a quality cosmetic finish is achieved when customising with images.
Interim Socket Fabrication
Your first limb following amputation is known as an interim prosthesis. This is because it is only used for a short time, typically a period of a few months. Why such a short time? Following amputation, your residual limb will shrink and change shape as the muscles waste away (muscle atrophy).
An interim socket is intended to be used during this initial period of rapid muscle atrophy. The time frame to stabilising is different for everyone, as is the shape or how your muscles will change over time.
Interim sockets are made using similar prosthetic materials and methods as diagnostic sockets, for adjustability during the initial post amputation period. Once residual limb volume has stabilised, a new cast will be taken so that a diagnostic socket and later definitive socket can be manufactured.
For more information, read our resources about the processes involved in being a new amputee, support services and amputee peer support
Specialised Sockets
Exoskeletal socket fabrication
For a more cosmetically shaped prosthesis, the socket can be laminated down to the foot or hand and shaped to closely match the shape of your sound side limb, this is known as an Exoskeletal Prosthesis (Exo for short!). This design removes the need for standard tube clamps and pylons (known as a modular or endoskeletal prosthesis). An exo design has a few extra steps involved.
Over the first lamination as above, the APC technician pours a two-part expanding foam around the socket on the transfer jig down to the adapter. Sometimes an aluminium or carbon puck is used, or in upper limb this is where the joint’s attachment site will be attached to the socket. Once the foam is hardened, the technician precisely carves the shape of the limb according to the client’s measurements of their sound side. Exoskeletal prosthetic sockets include two additional laminations to gain strength and finish with a cosmetic appearance. This style of socket is commonly used for upper limb prostheses, and for waterproof prostheses. Some benefits of this design are that these prostheses are lightweight and have fewer components which might otherwise rust.
Recreational socket fabrication
The initiation of the National Disability Insurance Scheme (NDIS) has allowed many clients the opportunity to explore a recreational prosthesis such as running blades, rock climbing arms/legs, weight-lifting arms, surfing legs, cycling legs and many more. The custom design and materials used in prosthetics, allow for many recreational prostheses to be achieved.
The final definitive prostheses for recreational limbs reflect the great deal of detailed hours undertaken by both the prosthetist and technician to create custom-manufactured prosthetic sockets. This follows the same steps as everyday and waterproof limbs, using similar materials and processes to laminate the socket.
If this is a part of your goals, or something that may interests you long term, make sure you talk to your prosthetist to include a recreational limb in your funding request. For more information about planning for NDIS and goals click to see our NDIS page.
For more information on materials used for prosthetics please get in contact with the team below.
