The Casting Procedure

View the previous video in the series: Meeting Your Practitioner

View the next video in the series: The Check Socket Fitting

The casting procedure in an appointment when you work with the practitioner to acquire the shape of your residual limb. The resultant shape is called an impression. The impression is what’s used to build your socket. Keep in mind that there are many different methods and techniques for taking an impression, so your experience my vary slightly, but the aim of this page is to give you a glimpse at what’s involved during the casting procedure.

Creating an impression is accomplished by either casting the limb or using a CAD/CAM scanning system. Here’s an overview of each method:

Casting – The practitioner will apply a layer of either Paster-of-Paris or Fiberglass casting rolls to the limb in a very specific manner. The casting roll is submerged in water just before it’s applied to your limb setting in motion a chemical reaction that causes the material to harden in just a few minutes. After it hardens, the impression can be easily removed from the limb. While the material is still not yet hardened, the practitioner will massage and manipulate the impression, applying pressure in specific areas. By doing this, the practitioner is manipulating the skeletal anatomy and soft tissue of your limb. The technique the practitioner uses is often a result of their experience, skill and training and just about every practitioner has their own personal method. Many different factors influence how the impression turns out such as, the temperature of the water, the width of the casting roll and the thickness of the material applied.

CAD/CAM scanning – Not as “hands-on” as casting, scanning uses a computerized program to create a three dimensional digital representation of your limb, accurate to within fractions of a millimeter. The scanning process doesn’t manipulate the soft tissue of your limb, rather, it digitizes only the surface shape of your limb. The practitioner then uses a computer program to alter the digitization, typically done in a very proprietary way.

Both the casting and scanning methods aim to achieve the same result, a comfortable and highly-functional socket.

Gel Liner Fitting

Because you wear the prosthesis with a liner, your practitioner will cast over the liner too. Before the casting is performed, you will work with your practitioner to apply your liner, making sure you’re fit with the appropriate size. Then, in many cases, the practitioner will apply a thin barrier over the liner, such as plastic wrap or a nylon stocking, to prevent the casting material from soiling the liner. This barrier also serves as a place where anatomical marks can be made.

Measurements

There are specific anatomical measurements that are very important to the process involved in creating your socket, so prior to taking your impression, your practitioner will use a few different instruments to acquire this data.

Anatomical Marking

Remember that your residual limb isn’t designed to bear your weight, so your socket is built to apply pressure in specific areas and relieve pressure from others. Your practitioner will use an special pencil to mark the boney and soft anatomical landmarks. These markings transfer to the inside surface of the casting material and note areas of significance to the practitioner as they create your socket.

Taking the Impression

Once both the measurements have been taken and the anatomical markings made, it’s time to apply the casting material. Throughout the casting procedure, listen for minor instructions from your practitioner as they work (i.e. adjust the bend in your knee, etc.). Once the rolls have been applied, it only takes 3-5 minutes to harden. That’s it!

After the casting procedure is completed, your practitioner will get to work building your check socket. This process takes a few days to complete, so you’ll return then for your Check Socket Fitting.

A Few Pointers…

The casting procedure can be messy, especially if Plaster-of-Paris is used, so be sure to bring a towel.
Since your practitioner will need access to your leg, be sure to bring a pair of shorts you can change in to for the casting.
If possible, bring a loved one with you to the appointment for moral support. A lot of information is thrown at you during these appointments, so having a second set of ears can be very helpful.

View the next video in the series: The Check Socket Fitting