How to Fabricate a Molded KAFO, Part I
September 2013 Issue
Of all the various orthotic devices, I fabricate molded KAFOs most often. While each molded KAFO (MKAFO) is distinct because of patients' varying needs, the basic approach and many of the techniques remain the same.
The process begins when you receive a patient's negative cast and fabrication instructions from the practitioner. It is good practice to confer with the practitioner directly if you need clarification or want to recommend material modifications based on the patient's profile. Whenever possible, try to work with the practitioner to keep the brace as lightweight as possible. Studies have shown if a patient has to expend more energy to ambulate when wearing the device, he or she is less likely to comply. So, from my experience working with practitioners, we have found the patient is more receptive if the device is lightweight, lower profile, and more attractive. Once you have agreed on any design or material modifications, the actual fabrication work begins.
Set ankle and knee angles.
Set the ankle and knee angles as specified by the practitioner; an articulated ankle is usually set at 90 degrees on a 3/8-in. footplate to allow for heel height. Check the cast in both the sagittal and coronal planes, and if the patient can be corrected to 90 degrees, correct the cast to neutral. After setting the ankle angles, lay up the knee joints on the cast. Set the knee joint at knee height, and center it and the distal upright medially and laterally on the leg. If the proximal upright does not fall in the center of the thigh, flex or extend the knee until it will be able to lock out at 180 degrees.
Prepare cast and pour positive mold.
Once these corrections have been made, place your cast in a sandbox, supporting it in the corner and perhaps against the wall, with sand covering the foot. You will need to place a pipe inside the cast. Pipe placement is important because you do not want the pipe to be in the way when you drill the holes for squaring the ankle and knee joints. To set the pipe properly, mark the medial and lateral sides of the cast at knee height where the joint bushing and screw will be located, then place the pipe in front or behind those marks and as far anterior or posterior as possible from the malleolus. Keep the pipe about one inch from the bottom to keep the foot from breaking off. After the pipe is set properly, mix the plaster to a good consistency for pouring, and pour it into the cast. Tap the cast to remove air bubbles.
After the plaster has fully hardened, the cast can be stripped.
Modify plaster mold/positive cast.
First, go over the surface of the whole cast with a flat Surform to remove the high points and make the low points more visible. Use the Surform to lightly surface the foot then create a flat spot on the heel and forefoot so you can stand it up to check the alignment. Once the alignment is correct, you can see what other modifications need to be done to the foot, such as creating a buildup under the first metatarsal head.
For buildups, I prefer to use plaster mixed with Zonolite®, which is a finer version of vermiculite. I find that Zonolite makes it easier to see where your buildups are, sets faster, and makes it easier to smooth your cast. Buildups made with Zonolite are not as apt to fall off or start cracking. I also use this mixture to cover low areas in the trim lines and build up bony prominences. You should avoid the ankle area because you will be putting a rod through that area and have to allow room for placing coupling nuts and spacers.
After the buildups, finish the foot. You may need to extend the forefoot for a full-length footplate. Usually by this point the plaster/Zonolite has set enough to use a flat Surform to expose the high points. Next, take the buildups down slightly, and shape them to blend nicely back into the original cast. Make sure you do not take too much off the plantar surface of the foot so the alignment can be maintained.
Next, adjust the positive cast in a pipe vise so the knee is straight up to the ceiling, which provides the natural toe-out of the patient. Mark where the openings for the thigh and AFO sections are going to be. Now mix up more plaster/Zonolite and add it to the medial and lateral sides at the openings. When this sets up, file it flat to square those areas and keep them from rounding in. This will make it easier to shape the metal later and make the finished device easier for the patient to don and doff.
At this point, I stand the cast upright in a prosthetic jig. (I have modified the jig to hold two casts upright at one time, which allows me to check the alignment easily on a set of bilateral casts, positioned side by side.) Mark the ankle height, final AFO height, knee center, and distal thigh trim, trying to keep equal distance above and below knee center. Then mark 1¼-in. below the perineum on the medial side and at least 1-in. higher on the lateral side. Once all heights are marked, remove the cast from the jig and put the rolls on. Do not bring the roll completely around the distal thigh and AFO height to leave room where the metal will lay.
In the next installment of this two part series, I will cover finalizing measurements and finishing the KAFO.
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) to review chapters for a fabrication manual. She can be reached at