When done correctly, lamination of a blade-style prosthetic foot can provide a strong, stable, lightweight solution while still maximizing the benefits of a high-profile foot. The following steps assume a successful check socket has been completed and laminated as a carbon-fiber socket ready for alignment. Before starting the lamination process, read and understand the specific prosthesis manufacturer's instructions for any variations to the method described in this article.
Preparing the Socket
Roughen the outer surface of the laminated socket for good bonding and future definitive lamination. To create the base for the foot attachment, form a buildup on the distal and posterior aspect of the socket using a potting epoxy, which is often supplied with the foot, or a sealing-resin preparation that includes filler material such as SolkaFloc® and carbon strands (gunk). This material can be added with or without a distal lock in place, but the buildup should be wide enough to support the full width of the foot blade. A length of about two inches should be allowed from the top of the foot module (pylon) to where the support terminates (Figure 1). Once in place and cured, the material can be ground flat on the posterior aspect, allowing the foot blade to rest on this surface in the desired alignment. Next, determine the correct placement for height and make all bench alignments according to the manufacturer's recommendations and prosthetist's assessment. If alignment adjustments are needed during the fitting process, you will have to remove the foot and repeated this step with the adjusted alignment.
Preparing the Foot
Grind three to four notches into the posterior lateral corners of the proximal foot module (pylon) to allow the fiberglass and carbon fiber to bond during the temporary alignment and the definitive lamination. These notches should be spaced 3/8 - 5/8 inch apart and should be between 1/16 - 3/16 inch deep on medial and lateral edges (Figure 2). Bevel the proximal posterior and lateral edges to avoid sharp edges, and roughen the proximal surface of the foot where it will bond with the socket.
Attaching the Foot
Attach the foot module to the prepared surface on the socket using a bonding resin or epoxy. The alignment will need to be checked again during this process to ensure correct placement and height. Following the bonding procedure and verification of the desired alignment, wrap the proximal module (pylon) and socket using a quality fiberglass casting tape. Ensure adequate layering of the tape based on the user's weight and impact level. At this stage, Össur recommends that the user wears the prosthesis for at least one week before proceeding to definitive lamination (Figure 3).
If realignment is necessary, remove the fiberglass tape, change the alignment, and rewrap as before. We recommend placing a cut strip along the back center of the foot blade during wrapping to prevent cutting into the carbon fiber when the fiberglass tape is removed.
Preparing for Lamination and Layup
Once the optimal alignment has been achieved, it is time to laminate. Refill the socket with plaster and insert a mandrel to allow for placement in a lamination jig. Remove the fiberglass tape, leaving the foot module attached, and begin the carbon/ fiberglass cloth layup.
Layup starts with cutting carbon fiber and Nyglass socking in 8- to 10-inch strips. Layup the cloth so that one third of its length is on the foot and the remaining two-thirds is on the socket. Layers of carbon fiber should be separated with a minimum of one layer of Nyglass. To strengthen the layup, add an additional layer of Nyglass between the carbon fiber to create the I-beam effect. The finished layup should resemble an Oreo cookie with a layer of carbon, two layers of Nyglass, and another layer of carbon. If more strength is needed, add one or two more layers of Nyglass and a third layer of carbon. Avoid applying two layers of carbon fiber directly against one another.
An alternate layup using only fiberglass is also possible (Figure 4). If desired for cosmesis, nylon or other material can be applied as the final layer.
During the layup process, ensure that the layers of material are tied into the notches of the proximal foot using a heavy thread or fiberglass strands. The material that is distal to the notch is then reflected back toward the socket after it is tied in. This will leave a smooth edge and prevent fabric from wrinkling during the lamination process (Figure 5).
Prior to lamination, the heel of the foot should be removed and set aside. Fill the heel bolt holes with putty to avoid any resin contamination, and then wrap the foot using a stretchy tape— preferably white in color—to avoid residue in the resin. Starting from the lowest end of the lamination cloth, wrap the foot all the way to the end of the toe. This will ensure the resin does not bond to the foot area that is not intended to be laminated. Once the foot is protected, pull the PVA bag over the foot and socket. Proceed with the routine lamination procedure, ensuring the resin effectively impregnates the cloth.
Once the resin has appropriately cured, remove the PVA bag and the tape protecting the foot. The system is ready for delivery.
Todd Schweizer, CPO, is the regional clinical manager for Össur Americas', Foothill Ranch, California, central region. He provides clinical and technical support for all Össur products and direct support for clinical customers in the central region.