Reducing Socket Size Without CAD
By Peter Panuncialman

Sometimes, due to changes in a patient’s residual limb, a prosthetic socket becomes too loose, and the patient needs to keep adding more and more plys of socks to make it fit. At this point, it is time to make the socket itself smaller and eliminate the need to wear socks.

For many technicians and practioners, reducing size accurately can be difficult. Many fabricators choose a CAD/CAM program to accomplish this task. While CAD can reduce plys automatically, ply thickness can vary. However, the cost of a CAD/CAM system can be prohibitive, and the thickness of any given ply is not easy to ascertain.

Variables that determine thickness are brand name, sizing and material choice (e.g., wool, acrylic, etc.). Sizing is critical because fabricators need to know how much stretch was applied to the sock. A short five-ply sock on a medium-length residual limb will stretch out the fabric to accommodate the length difference.

When using a CAD program, you will also not be able to place the socket into a transfer device to hold it while you are working on it.

Given these concerns, at Windy City Fabricators we choose to pour the diagnostic socket or definitive socket using the same brand and style of sock used in the fitting. This way we know precisely what thickness of sock the patient needs.

I have seen a version of this process done with glue to hold the sock in place. This can be a messy and time-consuming chore. I find it easy and effective simply to hold the sock in place when pouring. No tape is needed to close off the proximal end; the sock will control flow-over.

Step 1
Lock your socket into your transfer device. This will both preserve the alignment and leave your hands free to work.

Step 2
Position your residual limb sock into the socket and fold the proximal portion of the sock over the trim line of your socket. Make sure your sock expands into the socket and is free of wrinkles. If wrinkles are left in your sock prior to the pour, your mold may have crevices in it when the sock is removed. The process can safely be used with up to 2 socks of 5-ply each, for a total of 10 plys.

Step 3
After making a thick slurry of plaster, pour the plaster only two-thirds of the way up the socket. Lightly tug the sock to minimize wrinkles, visually checking for contact.

Step 4
Lower your pipe into the socket, keeping it a half-inch from the bottom. Fill the remainder of the socket with the plaster, keeping the sock extended proximally.
 
Step 5
When your socket/sock is filled, apply downward pressure to the plaster, assuring contact in the proximal medial lateral portion of the socket.

Step 6
Removal of the socket can be done in two ways:

1. Cut off your socket with a cast saw (this technique requires mold repair).
2. Using a wood block and a hammer, lightly tap the proximal edge of your socket. This technique is good for 90 percent of the sockets fabricators encounter.

Step 7
You must clean up the mold because of the impressions the sock leaves. A light smoothing will blend away any impressions. Turning the sock inside out will help minimize cleanup.

After these seven steps, your mold will be reduced by the thickness of the sock.

You can then proceed with fabricating a new socket that will be reduced in volume for the patient’s comfort.

Peter Panuncialman is president of OPTA and the owner of Windy City Fabricators in Chicago, Ill. For more information about this process, contact him at (773) 583-4860.