Fabrication Using the RevoFit Lamination Kit
May 2015 Issue
Many P&O devices require straps or laces to facilitate donning and doffing, provide ease of access, or allow control of the device. Often practitioners must try to create an adjustable system to allow for volume fluctuation. The RevoFit lamination kit is a Boa®-based cable system that can be laminated into a prosthetic or orthotic device. The original concept was to create a system that allowed finite adjustability for volume control, but it has since been expanded to encompass a variety of additional applications.
The system consists of a lamination tool/bayonet, high-power dial, guide tube, HD filament, wire feeder, and T6 tool (Figure 1). It is available in two versions to allow for increased design capacity: one in which the cable/ filament enters/exits the bayonet at parallel ports, and one with an inline (180 degrees) unit.
The fabrication sequence is the same whether you are making an adjustable socket or a closure system for an orthotic device. When fabricating an adjustable socket, an inner flexible socket or insert is recommended since it will allow for even pressure distribution when tightening the socket panels. Start by applying a PVA bag over the model you are working on, and then laminate a skin base. The layup will vary based upon what you are fabricating and the intended application. It is recommended that you reinforce areas that will be under stress from the HD filament excursion (Figure 2).
When the skin lamination has cured, remove the outer PVA and abrade the surface of the model with medium-grit sandpaper. This will improve the adhesion of the bayonet and guide tube to the model. Draw the anticipated window panels or openings and the guide tube path on the model. The model in this example is designed for volume control over a flexible inner socket. I've drawn the planned panels on the model in white and the guide tube path in red. Then determine where the lamination bayonet will be and bond it in place using Fabtech Systems' +PLUSeries® adhesive. At this time you can also bond other components to the model, such as an attachment plate. The bayonet has a small red dot on its surface. Make a note where this mark is for future finishing (Figure 3).
The next step is to bond the guide tube to the model. It is essential that you fill the Teflon® tube with putty to prevent the intrusion of resin into the guide tube. If there is resin intrusion, the only remedy is to strip and refabricate.
Once you have filled the ends of the Teflon tube with putty, bond the guide tube to the model. The manufacturer directions mention using spray adhesive. Spray a liberal amount of adhesive into a paper mixing cup, and use a small, disposable paintbrush to apply the adhesive from the cup onto the guide tube path drawn on the model. Then spray the guide tube with adhesive. When the adhesive gets tacky, apply the guide tube to the drawn path on the model. Be cautious when bending the guide tube around curves as it can crimp easily, which will cause a blockage in the tube and prevent the installation of the HD filament. Start the application of the tube by inserting at least one-half inch of the tube into one port of the bayonet; the bayonet is prefilled with silicone to prevent resin intrusion. Insert the end of the tube into the silicone. Adhere the guide tube following the planned path. Once you get back to the bayonet, cut the Teflon to the required length, fill with putty, and then insert it into the opposite port of the bayonet (Figure 4).
An alternative guide tube bonding method is to remove the fabric that covers the Teflon and then use sandpaper to lightly abrade the gloss off the Teflon. To adhere the tube, use small tack welds of 60 Second +PLUSeries adhesive. Start by affixing the guide tube to the desired path with small pieces of masking tape, and then apply small amounts of adhesive along the path. Avoid applying adhesive at trim marks. As the adhesive starts to cure, you can mold it slightly to smooth it (Figure 5). Be sure to wear disposable gloves while performing this step.
I prefer this method because using spray adhesive can affect the flow of resin through the guide tube during the final lamination, making it more difficult and resulting in a heavier model. When using the tack welding technique, the resin can flow under the guide tube and around the welds, which creates a nicer finish and lighter socket.
When the spray adhesive or tack welds are cured, apply your final fabric layup and perform the final lamination. Once the lamination is cured, remove the socket from the model prior to cutting window panels or openings. This will prevent damage to the inner flexible socket or insert. Draw the trim lines and cutouts on the socket (Figure 6). I use an electric cast saw with a modified cast saw blade, which makes the tight curves easier to trim.
After cutting out the panels, sand and polish the edges of the socket and panels. Sand the surface of the bayonet to expose the silicone. Remove the silicone and use a razor or utility knife to trim the Teflon that was pressed into it. Clean the edges of the panels where you cut through the Teflon tubing. To assist with volume control, bond on one-eighth inch or thicker Pelite padding, which will raise the panels from the model. As the patient tightens the unit, the HD filament excursion will pull the pads into the model causing compression to tighten the fit.
The final step is to assemble the system by lacing the HD filament through the panels and socket. Use the provided wire feeder, which has an opening similar to the eye of a needle. Pass about one inch of the HD filament through the opening and squeeze it closed, then feed the HD filament through the high-power dial, the guide tube, and then back to the high-power dial. The wire feeder will also clean any sanding and polishing debris from the guide tube prior to insertion of the HD filament. Start by tying a small knot into the opposite end of the HD filament. There are two ports on top of the high-power dial. Pass the wire feeder through one of the ports (Figure 7), and then pass it through one of the ports of the laminated bayonet. Continue to lace through the panels and socket according to the path you created (Figure 8). The lacing will end back at the opposite port of the bayonet. After passing through the bayonet, finalize it at the dial (Figure 9). I generally leave about one inch of excess HD filament prior to trimming and tying the final knot. Use a heated razor blade for the final cut since the HD filament is tough to cut.
The last step in the lacing process is to install the dial into the bayonet. However, you need to prepare the bayonet for future removal of the dial. Previously I mentioned that when you bond the bayonet to the model you should note the red dot marked on it. Now drill a small pilot hole through the lamination into the bayonet where the red dot is marked. This is an access hole to allow a technician to use the T6 tool to remove the dial in order to replace the HD filament as it wears. Once you have done this, insert the dial into the bayonet and turn it clockwise to snap into place. You can now tighten the panels by turning the dial clockwise. The dial can be pulled out and pushed in to release and engage the dial once it's installed into the bayonet (Figure 10).
Once you have learned the basic techniques of fabrication using the RevoFit lamination kit, your design options are whatever you can create. I have used this system on numerous lower- and upper-limb prostheses as well as on orthotic devices.
Glenn Hutnick, CPO, CTP, FAAOP, is director of prosthetics at Eschen Prosthetic and Orthotic Laboratories, New York, and president of Hutnick Rehab Support Central Fabrication, Bohemia, New York. He is also the chair of the American Academy of Orthotists and Prosthetists' Fabrication Sciences Society.