How is a Prosthesis Made?

There are thee stages to making a prosthetic limb.

• Measurement
• Rectification
• Fabrication

Measurement
The first step is to make a model of the prosthesis is to be fitted. Your prosthetist will take various measurements of your stump and your sound limb, followed up a plaster cast using plaster of paris of your residual limb (stump). This is sometimes supported by a digital image of the residual limb. This can take between 20 to 40 minutes.  A positive mould is subsequently created by filling the wrap cast with plaster of paris.
Rectification
The first stage is to take measurements from the plaster mould and compare these to the original measurements taken from the residual limb. The prosthetist will use the measurements and their own experience of socket design to adapt the mould to the needs of each patient through adding and removing plaster to ensure the amputee will bear weight where the residual limb is pressure tolerant and relieve pressure where the residual limb is intolerant. The objective is to design a comfortable socket which allows weight-bearing. At the fitting stage you will work with your prosthetist to make minor adjustments to improve the comfort of the socket.
Fabrication
At this stage a Check or Test socket is made using a square sheets of material, generally polypropylene, which is heated and then placed over the positive cast. The thermoplastic is moulded to the cast and allowed to cool. Preliminary fittings are carried out using the check socket, which is clear, so that minor adjustment can be achieved through reheating the socket. When the prosthetist and the amputee are happy with the fit a definitive socket is made. A positive plaster mould is recreated from the check socket. This can be either vacuum formed by draping heated thermoplastics over the positive mould or by applying layers of woven materials together with acrylic resins over the positive mould.

Once the socket has been created the liner locking mechanism is attached. This is the mechanism which attached the socket to the liner which is worn against the skin of the residual limb (stump). This is only necessary for sockets using a locking mechanism for the suspension of the socket. The other components of the artificial limb are incorporated. The prosthetist generally supervises the assembly of the prostheses by the prosthetic technician.

Sources
Prosthetic sockets fabrication using rapid prototyping technology, P. Ng, P.S.V. Lee, J.C.H. Goh
Adinbrooke Hospital Articifial Limb Service website
IDS, Cappagh National Orthopaedic Hospital, Dublin, Ireland website