How to Fabricate a Molded KAFO, Part II

In the first installment of this series ( The O&P EDGE , September 2013), I covered creating a positive mold and surfacing the mold. We also marked our ankle height, final AFO height, knee center, and distal thigh trim. In this installment, we'll finalize and assemble the molded KAFO (MKAFO) and apply the finishing touches. Square the knee and ankle joints. Lay up the knee joints on the cast and mark the centers where the screws and bushings will be. (Author's note: Especially for posterior offset knee joints, this will not be the center of the cast.) The height is already marked, so now you have the exact point at which the knee joint will be placed. Position the cast with the knee straight up, allowing the natural toe-out, and draw a line from the center of the knee screw hole on the medial side to the center of the screw hole on the lateral side. Then go to the bottom of the cast and hold a pencil from the center of each knee joint mark to check the alignment visually. Once that is done, align the drill bit-I use a 3/8-in. bit-with the line you drew at the knee, hold the drill parallel to the floor, and drill about halfway through the plaster mold from each side until the holes meet. Blow out the hole, put a threaded rod through it, and then put nuts on the rod to act as spacers. My rule of thumb is to start with 3/16-in. spacing on the lateral side and ¼-in. spacing on the medial side. The size and shape of the patient's leg, as well as if there is genu valgum or genu varum at the knee, will determine if you need to allow more than the standard amount of space to prevent the knee joints from rubbing against the patient's leg. Now that the knee is done, we can proceed to the ankle. [caption id="" align="alignnone" width="500"] The uprights have been shaped over the plastic, which was vacuum formed over the cast. A threaded rod, with nuts used for spacers, is inserted through the cast to aid in squaring the knee joints.[/caption] Drilling through the ankle portion of the cast is a little different from drilling through the knee because of the tibial torsion. Normally the lateral malleolus falls at about the center of the leg while the medial malleolus is positioned farther forward. Mark the height and the apex of the malleoli. Turn the cast so the centers of the malleoli are in line with each other and parallel to the floor. Draw a line from one malleolus to the other as a guide to follow with the drill bit. Now drill about halfway through each side with a 7/32-in. bit until the two holes meet. Blow out the hole and insert the rod. For the next step, back out the rod 1½ in. or so. Use a 3/8-in. bit to enlarge that same hole, only going in about 1-in. deep on each side. I use the OTS kit for any joints with a 3/8-in. hole. With the rod in place, tap in coupling nuts just far enough to serve as spacers. With the rod going through each coupling nut, I know they are square to each other. If there is any play in the coupling nuts, take fast-fix glue (or Super Glue) and secure the nuts in the cast, then remove the rod. The kit has long setscrews that then can be screwed into the coupling nuts. With a spacer (the kind you use when squaring metal KAFOs) in the ankle joint, you can now slide the joint on and off, making sure it is flat on the coupling nut when shaping the stirrup and the distal upright. Secure ankle joints and stirrups. Proceed to shape the stirrups. After the stirrups are shaped, the joints and stirrups can be secured with a nut so they'll remain in place when you are pulling the plastic. At this point, center punch where you want to put each of the holes, which may vary depending on the stirrup manufacturer. Then drill and tap the holes. I add plaster under the stirrups and joints to hold them in place and keep the plastic from pulling under them. Depending on whether you want the uprights on top of your plastic or underneath it will change the order in which you perform some of these steps. I usually shape my stirrups and ankle joints, then pull my plastic. While the plastic is in the oven, prepare the plaster mold by wrapping the ankle joints with at least ¼-in.-thick AliPlast or Plastazote that has been preheated so it will shape well over the joints. I add extra padding in the dips so later it will be easier to cut the plastic off in those areas, but be careful to keep the padding out of the trim lines. Then wrap the padded ankle joints with electrical tape. Put a stocking over the cast for an air wick and then pull the plastic. After the plastic has cooled, cut away the plastic at the knee and ankle, and then shape the knee joints and uprights. Make edge bends first, then contours, then any twists. The next step is to determine how much of the distal bars need to be cut off at the point where they meet the ankle joints. Take off a little at a time to avoid cutting too much. Once everything is shaped, mark the hole placements on the uprights, taking into account where to attach straps, chafe, and loops. I drill 13/64-in. holes in the metal, and then put the knee joints back on the cast and secure them. Now use the holes drilled through the metal as a guide to drill through the plastic. Cut the plastic off the cast and trim out as you normally would. Finishing touches and assembly. [caption id="" align="alignnone" width="250"] The finished MKAFOs.[/caption] For the final steps, first remove any nicks and buff all metal parts. Alternatives include sand blasting the metal then spraying it with a clear acrylic, adding a powder coating, or even shrink wrapping the metal. When this is done, assemble the MKAFO. For an adult MKAFO I use Chicago screws to attach the knee joint uprights to the plastic. For a child MKAFO I use 8/32-in. screws. This way I can drill a smaller hole in the metal. Then I run the screw from the inside of the plastic into the tapped hole in the metal. Check that your joints are still square. If everything is square, make the straps and tongue and place any padding. A lot of the MKAFOs I fabricate also get a lever release. So as part of this step, I determine how I want the cables to run and attach them. Add finishing touches such as padding, joint covers, or customized straps, and clean your brace. Make sure the knee and ankle joints move freely. (Author's note: A little brace ease goes a long way.) Check that the knee joints lock and unlock when they should and that any drop locks completely engage without being forced. Always check the bail locks very carefully. Remember, a lot of orthotic parts are not machined as precisely as we'd like. It's not uncommon to have to make some adjustments to make your parts function properly. Finally, use Loctite on all screws used in the fabrication of the device. Good luck, and if you have any questions, I'd be happy to help. Louise Bensley, CTPO, has 24 years of experience in O&P fabrication and is currently on the advisory board for the Orthotic & Prosthetic Technological Association (OPTA) reviewing chapters for a fabrication manual. She can be reached at bracemaker7292@msn.com.

How to Fabricate a Molded KAFO, Part II

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How to Fabricate a Molded KAFO, Part II

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