My New Leg

At the end of my May 8 posting about getting cast for the socket of my new leg, I mentioned Wayne would be using the cast to create a check socket. A check socket is pretty much what it sounds like: a prototype of a socket used to evaluate and adjust the fit prior to making the final socket for a finished prosthesis. Check sockets are made from a transparent thermoplastic (usually polyethylene), meaning a plastic that changes shape when heated and becomes hard when cooled.

The transparency allows the prosthetist and amputeee to work together to identify problems with the socket’s fit, and be able to actually see the problem areas and mark them with a Sharpie pen. The thermoplasticity allows the prosthetist to use a heatgun (essentially a glorified, extremely hot hair dryer) to heat up localized spots in the socket and deform them to improve the fit of the prosthesis. The prosthetist can also use a grinder to grind out areas of the inside of the socket, if necessary.

After taking the cast of my stump, in preparation for fitting the check socket, Wayne and his shop technicians “pulled a check socket” for me. Wayne was kind enough to take photos of the process of making the check socket in between my appointments, to which I’ve added a brief description.

First, the technician starts with the finished cast Wayne made of my stump in the previous appointment.

Then the tech mixes up a bucket of plaster. It’s important to use warm water because cold will take too long to set up and hot will set up too quickly and may deform the cast.

The tech pours the plaster into the cast, which serves as a mold.

The plaster dries to become a positive model of my stump which can be sculpted. The metal dowel will allow Wayne or the tech to hold the positive in a jig and work on it later.

When the plaster is dry, the tech cuts open the cast and…

…strips it off the positive. (This is a beautiful example; when I’ve done this, the plaster always sticks to the cast, which makes it a bit tricky to strip.)

Wayne will also make a foam insert for the bottom of the check socket. It allows more room for error so we don’t have to get the length of the socket exactly correct when checking the fit, but I still won’t painfully bang the end of my stump on the bottom of the socket.

The tech shaps the foam insert on the sander so it will fit snugly into the bottom of the socket.

The positive model is now upside down and held in a jig by the metal dowel. The white plastic locking mechanism (that holds the silicone sleeve on my stump in the socket) and the foam insert are on top of the bottom of the model, ready for the socket to be pulled.

A sheet of polyethylene is mounted on a metal hoop framework and warmed up in the oven until is is pliable.

The tech holds the metal framework to pull the soft, hot plastic over the inverted cast.

When the plastic is pulled over the cast, the tech turns on a vacuum (pulling through the pipe in the jig below) that pulls the plastic tightly down onto the cast.

Once the plastic has cooled and hardened, he uses a circular saw to cut out the socket from the jig platform.

The tech uses an air hammer (the squarish metal tool poking into the socket) to remove the plaster from the socket. Air hammers are essentially hand-held jackhammers and you have to be careful not to nick the inside of the socket.

Voila! The top of the check socket, cleared of plaster and ready to be finished. The black lines are the trimlines (the edges of the socket).

The next steps are to cut the trimlines and smooth the edges on the sander. Then Wayne used a resin to glue a pyramid adapter to the bottom of the socket so he can attach a foot to the socket, and finished assembling the lock in the bottom of the socket.