Fixing a Leaky Socket
By David Peterson

I am one of three technicians on staff at Monroe BioTechnology in Green Bay, Wisconsin. We have an on-site lab, which gives us fast turnaround times for fabrication, as well as access to all our technicians’ skills throughout the day as problems arise. And in the realm of fabrication problems, nothing can be more challenging than repairs.

Fabricating an airtight socket
The best way to fix a leak is to avoid it in the first place. When we fabricate sockets, we should do our best to make them airtight.

Transtibial sockets
At our lab, a standard transtibial socket, without the use of a pin and liner, has a distal void with a flat end. The distal buildup allows us to use flat socket attachment plates and custom end pads. We avoid using plastazote end pads, which are time-consuming to create, difficult to fabricate over without crushing out the foam and hard to duplicate if the pad needs to be replaced. We suspend the socket with a Durasleeve® neoprene suspension sleeve. This creates an airtight system where the vacuum pressure acts as a secondary means of suspension.

We fabricate our transtibial sockets over square aluminum plates. We attach four-hole pyramids to the sockets, fit the devices on the patients, and dynamically inject custom silicone foam end pads. To inject the end pad, we drill a hole where we believe the anterior proximal edge of the pad will end.

When we’re done making a socket, it has four distal holes for the attachment plate, as well as a hole from injecting the distal end pad. If we don’t seal these holes, air can leak into the socket, and the patient’s residual limb will likely piston inside the socket.

Transfemoral sockets
Air leaks are a major concern when fitting transfemoral suction sockets. It doesn’t matter what type
of valve a technician uses—eventually the system leaks, and air works its way into the socket. Then it’s our job to diagnose where the problem is coming from. When the socket fit has been adjusted with padding, air has channels to follow at the edges of the pads. In transfemoral sockets, we need to check the valve, the valve housing, and the padding as potential sources for leaks; and then, one by one, eliminate them as suspects of the problem.

Checking for leaks
Over the years, we have used many different methods to check a socket for leaks, but some work better than others. In a pinch, you can seal the sleeve or use a hot-water drip, but we find the balloon test to be the most reliable.

Sealing the sleeve
One way is to fold the top of a neoprene sleeve to make an airtight seal. Push the excess air out and then pull up on the sleeve. If the socket has a leak, the sleeve inflates as you pull up on it. The drawbacks of this method are twofold. It’s sometimes difficult to achieve an airtight seal with the sleeve, and using the sleeve for a leak check does not eliminate the sleeve as a possible source of the leak.

The hot-water drip
When checking a transfemoral socket for leaks, a common method is to fill the socket with hot water and wait for the telltale drip. Hot water has a lower viscosity than cold water and will flow more easily through leaks.

The problems with this method are multiple. Water molecules are larger than air molecules and are less likely to flow through very small leaks. Also, you have to dry the entire socket and the valve when you’re done. That’s not difficult, but it does take time. Do not use this method when the patient has been fit with a C-Leg®. The last time I checked, soaking a C-Leg in water voids the warranty. Try explaining that mistake to your boss! The water leak-check method also does not work if you are using a valve with an auto-expulsion feature.

The balloon test
At Monroe, we have developed an easy, foolproof method to isolate air leaks to the socket environment. Start with latex balloons that have a large mouth to them. One possible source is Daw Industries’ Optiflates®.

Begin by stretching the mouth of the balloon over the trim line of the socket. Stretch the balloon beyond the trim line and remove any wrinkles in the balloon where it touches the socket. Push the excess balloon into the socket to drive out some of the extra air. When working with a transfemoral valve, you may want to push the valve button to help the air escape the system.

After expelling some of the air, pull up on the balloon. Hold the balloon under a constant amount of tension for up to 30 seconds. If you can see the balloon moving while it’s under constant tension, the socket has a leak.

If the socket doesn’t leak, then the problem rests with the suspension, such as a hole in a sleeve or a failed seal on a sock or liner. Or perhaps the socket doesn’t fit the patient anymore and suction cannot be maintained. Using this leak check method is quick and requires no cleanup. It should pinpoint the leak to the socket or to the fit of the socket.

Fixing the leak
When you find that your socket has a leak, the obvious next step is to locate it and fix it. With transtibial sockets, I start by filling the attachment holes with aquarium sealant. If the socket still leaks, then I look for any other holes that may be leaking and fill them with acrylic resin or silicone. If all reasonable measures have been taken, and the socket still leaks, replace your neoprene sleeve. Even if you can’t see a hole, the patient has probably worn one into the sleeve.

When locating a leak in a transfemoral socket, start with the valve. Replace it with a new valve and check for leaks again. If the socket still leaks, then your housing is the likely culprit. Take whatever means necessary to create an airtight seal. The method used will vary depending on the style of valve used and the socket material you are working with. If possible, replace the housing to eliminate it as a possible problem area. If the fit of the socket has been altered with pads, seal the edges of the pads with tape. This will eliminate most of the air channels and help the suction socket remain sealed against the patient’s limb.

It may take a few steps to locate an elusive leak and to seal the socket. But your time will be more than repaid by knowing how much the patient will appreciate having a prosthesis that feels more like a part of him.

David “Commander Dave” Peterson is a technician at Monroe BioTechnology in Green Bay, Wis.