The Essential Guide to KAFO Fabrication Part 1
As a former steelworker, I see great similarity between building an office tower and fabricating a KAFO. Regardless of the architect or contractor, every skyscraper starts with the foundation, followed by the steel framework, the exterior, and then the interior.
The scale may differ, but KAFO fabrication is also guided by a universal process. Regardless of which components are used, whether the knee joint is mechanical or electronic, whether the knee is locked or free swinging, and whether or not the orthosis has stance control, the same three steps are required for every KAFO:
- Prepare a negative wrap.
- Set up the proper alignment.
- Incorporate modifications in a plaster cast.
This column-the first in a series of three-focuses on the crucial first step. Preparing a negative wrap is time-consuming. Following the proven method outlined below will help to ensure that the job is done right.
Inspect. Make sure the negative wrap is usable. On occasion, we receive a wrap that collapsed because it had not cured properly or was damaged in shipping.
Figure 1. Staple along the cut line, making sure the two sides align correctly.
Figure 2. With the heel on a flat surface, measure and mark the knee height with horizontal lines on the medial and lateral sides of the negative wrap.
Review the instruction sheet. Otto Bock asks practitioners to use our standardized measurement form. At a minimum, you need six measurements: medial and lateral ankle heights; knee height; medial-to-lateral (ML) measurement of the knee and ankle; and overall height of the KAFO. The more information, the better the fit, so we welcome additional measurements such as circumference of the limb at various points and other ML and anterior-to-posterior (AP) measurements.
Read through the practitioner's instructions about any requested corrections. In a perfect world, there would be no corrections. (See "The Ideal Wrap Captures Alignment" sidebar.) But corrections are a fact of life in real-world orthosis fabrication.
If any critical measurements are missing or you have questions about the instructions, make a follow-up call to the practitioner.
Staple. Negative wraps come to us in various configurations: taped together at the cutoff seam; in two pieces split at the knee; or un-taped. If the practitioner did not draw alignment marks crossing the cut line, match up the fiber pattern and draw alignment marks across the cut line. Remove the cotton stockinette because it gets in the way in later steps.
Staple along the cut line, making sure the two sides align correctly (Figure 1). Use just enough staples to hold the edges in place, about every three inches or so. The staples stabilize the negative wrap during the casting process but will have to be removed later, so fewer is better.
Mark landmarks. Compare measurements on the instruction sheet to bone landmarks on the negative wrap. If they don't match, call the practitioner.
Figure 3. With the heel on a flat surface, measure and, on either side of the ankle, mark a horizontal line at the average of the medial and lateral malleolus heights.
Figure 4. With the back of the heel against a perpendicular surface, measure and mark a vertical line at the average of the sagittal measurements on each side of the ankle. The lines cross at the ankel's axis.
With the heel on a flat surface, measure and mark the patella. Measure and mark the knee height with horizontal lines on the medial and lateral sides of the negative wrap (Figure 2). Extend the lines to complete the circumference. Measure and mark the medial height on the medial side of the ankle, and the lateral height on the lateral side. These ensure that the center of rotation in the KAFO's joints work in synch with the anatomical joints. Now you're ready to make any corrections marked on the instruction sheet.
Make corrections. A correction always involves making a wedge cut on one side of the negative wrap and a single, horizontal cut on the opposite side. The two cuts allow the cast to flex into the wedge and extend on the opposite side.
To mark the wedge, use a horizontal line at the joint axis as the midline. Draw a gentle arc above the midline and a gentle, inverted arc below the midline. The height of the wedge formed by the two arcs should range from 3/8 to one inch, depending on the angle of correction: the bigger the correction angle, the larger the wedge.
With a cast saw, cut out the wedge and make a single cut two-to-three inches wide in the horizontal line on the opposite side. Then insert and adjust one or more tongue depressors in the slice on the opposite side until the correction matches the prescribed angle on a goniometer.
Stabilize the correction. If the remaining wedge is less than 3/8 inch, staple it and wrap plaster bandage around the joint, sealing the slice on the opposite side. If the gap is more than 3/8 inch, staple it, use fast-hardening putty to secure the desired angle, and wrap plaster bandage around the joint to seal the wedge and slice.
All corrections are basically done the same way. However, the following corrections require additional, specific instructions:
Ankle flexion correction: This is the most common correction we get at Otto Bock. First, find the ankle's axis point. The malleolus on the medial side is slightly higher and more anterior, relative to the lateral side. A quick way to determine the center of rotation is to split the difference between the medial and lateral apex of the malleoli.
Figure 5. Adjust the tongue depressors in the single cut until the lines above the wedge match the angle of the goniometer.
With the heel on a flat surface, measure and mark a horizontal line at the average of the medial and lateral malleolus heights on each side of the ankle (Figure 3). Then extend the lines to complete the circumference. Next, with the back of the heel against a perpendicular surface, measure and mark a vertical line at the average of the sagittal measurements on each side of the ankle. The lines cross at the ankle's axis (Figure 4).
If the practitioner requests a dorsiflexion correction, make an anterior wedge. For a plantarflexion correction-to add heel height, for example-make a posterior wedge. The horizontal line at the axis height is your midline. Draw the arcs for the wedge from one axis point to the other. To stabilize the negative wrap along the cut line, staple below the bottom line and above the top line of the wedge, or just above and just below the single cut.
Cut out the wedge and make a single cut on the opposite side. Set the goniometer to the prescribed angle. Adjust the tongue depressors in the single cut until the lines above the wedge match the angle of the goniometer (Figure 5), and stabilize the correction. A dorsiflexion correction will create a peak above the heel, which will have to be sanded off in the positive cast.
Figure 6. Using a caliper, measure the anterior-posterior depth of the knee at the horizontal line that marks the knee's height.
Figure 7. As an easy alternative, an Otto Bock Knee Pivot Gauge instantly zeroes in on the point that is 60 percent anterior.
Figure 8. Using a goniometer set at 90 degrees, draw a vertical line through the axis plus a parallel line along the upper calf on each side.
Heel correction: A valgus correction of the heel requires a medial wedge on the negative wrap. For a varus correction, make a lateral wedge. Mark the wedge by drawing arcs that meet the horizontal line at the anterior and the posterior.
Cut out the wedge and make a single cut in the horizontal line on the opposite side. Adjust the tongue depressors in the slice until the heel is in a neutral position. Stabilize the correction.
Knee extension or flexion correction: In addition to a prescribed correction, you may have to make a correction for the orthosis. Some KAFO knee joints, for instance, require five degrees of knee flexion to function properly.
Start by finding the knee's axis point. Using a caliper, measure the AP depth of the knee at the horizontal line that marks the knee's height (Figure 6). Because the knee's pivot point is 60 percent anterior, multiply the measurement by 0.6. (For example, 14.5cm x 0.6 = 8.7cm) As an easy alternative, an Otto Bock Knee Pivot Gauge instantly zeroes in on the point that is 60 percent anterior (Figure 7). Measure that distance from the anterior on the medial side and mark a vertical line. Repeat on the lateral side. The horizontal and vertical lines cross at the knee's axis.
If the practitioner requests additional knee flexion, make a posterior wedge. For an extension, make an anterior wedge. Mark the wedge by drawing arcs from one axis point to the other.
Using a goniometer set at 90 degrees, draw a vertical line through the axis plus a parallel line along the upper calf on each side (Figure 8).
Add staples along the cut line above and below where you plan to use the cast saw. Make the wedge cut, and slice on the horizontal line on the opposite side.
Set the goniometer to the prescribed angle and adjust the tongue depressors in the slice until the vertical lines match the angle of the goniometer. Make sure the correction does not alter the ML angle of the joint, then stabilize the correction.
Varus/valgus correction: A varus correction requires a lateral wedge. For a valgus correction, make a medial wedge. Mark the wedge by drawing arcs that meet the horizontal line at the anterior and the posterior. As with the ankle, a varus/valgus correction at the knee adjusts to neutral, so there is no need for a goniometer.
Cut out the wedge and make a single cut on the opposite side. Adjust the tongue depressors in the slice until the knee is in a neutral position, and stabilize the correction.
You're done preparing the negative wrap. Now you can move on to setting up the proper alignment, the topic of the next "Shop Talk."
The Ideal Wrap Captures Alignment
In my mind, the negative wrap doubles as the foundation and the superstructure of a construction project designed to support a dysfunctional lower limb. The entire process depends on the negative wrap being an accurate model of what the patient needs. The best way to ensure success in building a KAFO is to capture proper alignment while casting the negative wrap.
Adjustments cannot be made with the same precision as casting, and changing the position of the ankle or knee in the negative wrap changes muscle flexion in the patient. Bottom line: Corrections to the negative cast introduce uncertainty into the fit.
To get the best results for negative wraps, follow these tips:
Have the patient stand. Because weight bearing affects alignment and muscle tone, casting the patient in a supine position is a last resort.
Get the patient in the proper position. When casting, use pressure points to correct the patient's alignment. A good cast has finger marks embedded in the negative wrap, a sign that the practitioner was holding the patient in the correct alignment.
Incorporate heel height. Add the patient's choice of heel height to the foot casting board.
Use layers. With quick-curing products, it's best to divide and conquer. Focus on one layer at a time, and overlap one layer with the next layer. Otto Bock recommends a three-phase casting technique:
- Slipper cast to capture the correct alignment and correction of the foot.
- Ankle to calf to capture the correct alignment and correction of the ankle.
- Calf to thigh to capture the correct alignment of the knee.
Pedro Salazar is an orthotics fabrication specialist at Otto Bock US HealthCare, Minneapolis, Minnesota. He oversees all orthotic fabrication and provides training to new fabrication technicians at Otto Bock.
-
-
-
-
CONTACT US