How prosthetic legs are made

Every socket is made on a copy of one person's leg, so no two are the same.

stations: 6
things upstream: 45
raw sources: 15
steps from the ground: 7

The short version

A prosthetic leg is made around a custom socket. A prosthetist captures the shape of the residual limb with a plaster cast or a 3D scan, modifies the model to relieve pressure points, and forms a socket over it from thermoplastic or carbon fiber and epoxy resin. The socket is then joined to a knee, a pylon and a foot.

Capture the limb shape

A prosthetist casts the residual limb, sometimes using an air pressure system, or scans it digitally. Soft tissue changes shape under pressure, which makes this one of the hardest parts of the job.

Goes in
Plaster of Paris
Rectify the model

Plaster is added to the model over areas that will need relief from pressure and removed where the limb can bear load. This can be done by hand or in software.
Try a diagnostic socket

A test socket is formed over the model from transparent, heat-malleable plastic. It is not meant for permanent use, and it lets the prosthetist see whether the shape fits comfortably.

Goes in
Plastic
Form the final socket

The approved shape is wrapped with a heated sheet of thermoplastic or with carbon fiber coated in epoxy resin. Computerized models can also be 3D printed.

Goes in
Carbon fiber Epoxy Polypropylene
Attach liner, knee and foot

A silicone liner fits between limb and socket and is held by suction or a pin lock. The socket is joined to a pylon, and a knee joint and foot, in lightweight metals and composites.

Goes in
Silicone Titanium Aluminum
Align and fit

The parts are aligned with the wearer standing, a step called static alignment, then adjusted as the wearer walks. A rehabilitation team then works with the user.

End of the lineProsthetic leg

Worth repeating

A person with a leg missing above the knee uses roughly 80 percent more energy to walk.
The first commercially available microprocessor-controlled knee, the Intelligent Prosthesis, was released in 1993.
The first aluminum prosthesis was made by Marcel and Charles Desoutter.