There are a lot of different interfaces for prostheses, ranging from the classic Pelite liner to gel liners to flexible inner sockets. When selecting which interface to use, it is important to consider the patient’s needs and preferences. Some patients will be resistant to change. For instance, an 80-year-old person who has had an amputation for 60 years is likely going to want to stick with a Pelite liner if that is what he or she is used to. While Pelite liners can be used with a gel liner, sometimes the Pelite liner will not last the life of the socket or the gel liner. In some cases, the seams will come unglued, the Pelite can tear, and straps, if used, can come unstitched—in short, durability can be a problem. We came up with a way to make them more durable and modernize them.
There are many different materials that could be used to make a Pelite-type liner, including multidensity puffs or other types of preformed cones, but this article will focus on Pelite for its molding properties and its ease of use.
Tears and punctures are common in Pelite liners, but these problems can be remedied by adding an outer layer of Duraflex. To keep the bulk to a minimum, use a 1/8-inch-thick sheet of Pelite and a 1/8-inch-thick sheet of Duraflex; Proflex or other similar plastics could also be used, however, we use Duraflex most of the time. The fabrication is simple and only takes about one-half to one hour longer than fabricating a regular Pelite liner, depending on the type of socket and suspension you are fabricating. Fabrication procedures for a polypropylene socket and a laminated socket follow, both using a pin lock for suspension, as well as without a pin lock. We call this new interface the Duralite liner.
After the check socket fitting is satisfactory, use an alignment jig to capture the alignment. You can use the top of a used gel liner to top your check socket for pouring instead of plaster tape. I keep a few different sizes on hand for different sizes of transtibial sockets (Figure 1). If you want to use pull tabs on the Duralite liner, these can be built in, which makes stitching tabs after the fact unnecessary. Just be sure to extend the cast above the trim lines by 3 inches. Remove the positive mold from the check socket and round the distal edges where the lock dummy would be so that the Duralite liner will mate well between the gel liner and the interior of the socket. Polish the cast, and move the mold to a vacuum station (Figure 2). Measure the cast length and circumferences to make the Pelite cone. Cut out the Pelite and mark the edges for the posterior seam . inch from the edges to be beveled. After grinding the bevel, glue the seam together. With a fine sanding cone, sand the seam carefully until it feels flat. Then invert the cone.
Cut a 2- to 4-inch circle of Pelite for the distal pad. Heat the pad, and then hand form it over the distal end of the mold. We have found that using your stomach is a quick and easy way to push the end pad over the cast. It looks funny but works well. Bevel the edge of the pad, then secure it in place with a headless nail (Figure 2). Heat the cone in the oven until it is pliable, and pull it quickly over the mold with the seam placed posteriorly. Make sure the Pelite extends all the way up to cover the extra 3 inches for the pull tabs. Cut off the excess so the other end can be glued to the distal pad (Figure 3). Use a heat gun to make the flap edge pliable, and then stretch it over the distal pad; be careful not to wrinkle the distal pad. Pull a nylon over the mold, then pull a trash bag over the mold and vacuum it down; this will pull the Pelite onto the cast. Use a heat gun on the low setting to heat the Pelite, but be careful not to melt the trash bag; this will help pre-shape the Pelite to prevent wrinkles when the Duraflex is pulled over it. After it cools, remove the bag and nylon, and use the fine sanding cone to smooth the edges on the distal end and on the posterior seam.
Tie a knot at the end of a nylon, and pull it over the cast. Center the knot over the distal end and put Master or Barge glue around it (Figure 4). When the glue is dry, clip off the knot off of the nylon. Measure the length and largest circumference of the mold and cut the Duraflex large enough to drape mold over it. The Duraflex only takes between three and four minutes in a 400 degree oven to melt to operating temperature. Flip the cast so the seam is facing down, and then pull the Duraflex over the Pelite (Figure 5). Cut the seam as close to the cast as possible since it will be ground off. The heat will fuse the Duraflex to the Pelite. While it is still hot, a transfer pattern monogram could be laid onto it for added visual appeal (Figure 6). Use a heatgun after it is stuck on to ensure it transfers properly. When the plastic is cool, grind the seam off using the fine sanding cone, and then buff it with a blue buffing cone.
At this point, for a suction socket or simple patellar-tendon-bearing (PTB) socket with no lock, the prosthesis can be laminated. For sockets with pin locks, place the cast back in the alignment jig in preparation for the lamination dummy to be attached. Use plaster to attach the dummy to the Duraflex (Figure 7). After the plaster is dry, carefully remove the cast from the jig. If the dummy comes off, use Super Glue to reattach it in its proper position. At this point, an acrylic socket can be laminated using your usual procedures. For a polypropylene socket, pull a nylon over the cast, then pull a casting balloon over the cast. After you’ve completed that step, pull two more nylons over the cast. This prevents the polypropylene from fusing to the Duraflex. The polypropylene can be blister molded or drape molded and then cut off.
After the socket is cut off, remove the Duralite liner, and cut it to the trim lines that are needed. If the nylon fused to the Duralite liner, just use a blue buffing cone to buff it off. Trim the socket ½ inch below the Duralite liner’s trim line, and finish the socket.
For a socket using a pin lock, cut a hole in the bottom of the Duralite liner using a small grinding cone (Figure 8). It is sometimes necessary to use a medium-length pin with this interface. If the patient desires the pull tabs for donning, cut finger holes in the Duralite liner in the extra 3 inches that was added earlier (Figure 6).
The Duralite liner is more durable, less likely to delaminate, difficult to puncture, and similar in weight to a traditional Pelite liner. It is a great marriage of old technique and newer materials that maintains the benefits of thickness and the properties of a Pelite liner, and it can be billed as a flexible inner socket.
Travis Petersen BOCP, COA, works as a practitioner and technician at Alpha-Omega Orthotics & Prosthetics, Springfield, Missouri. He has also worked as a technician for other companies in Missouri. He can be contacted at .
