Modifying an AFO Positive Cast

Once the positive cast has been made, it gets modified. Modifying the outline is the basis for an optimal fitting as well as a harmonious look of the resulting AFO.

Producing the Work Basis

Step 1/1

Create a positive cast. Stick the alignment aids through the already marked mechanical pivot points on the negative cast and fill the negative cast with plaster. Let the plaster harden.
Note: Check the heel height on the h-Cast.

Reinforcing the Foot Piece

Step 1/2

Mark the 1st and 5th metatarsal bone. Determine the rolling-off line between the two markings. When you draw the line in, make sure that it is parallel to the mechanical joint axis (auxiliary line A).

Step 2/2

Place the positive cast with correct heel height on the h-Cast. Reinforce and prolong the foot area so that it provides more stability during later reinforcements.

Determining the Toe Spring

Step 1/4

In order to define the toe spring, determine approximately the trochanter first. Measure the distance from the ankle joint axis to the knee’s joint space. Double the number and determine a point B for the trochanter.

Step 2/4

Tie a string to a pen. The string’s length (R) should match the distance from the trochanter (B) to the rolling-off line (C) (R B - C).
Hold the string at the determined position of the trochanter (B) and place the pen at the rolling-off line (C). Use the pen to draw the circle line on the positive cast.

Step 3/4

Modify the forefoot area of the foot piece corresponding to the drawn marking.
Note: Modify the bottom and the top of the foot piece parallel to one another. This way, the screw clamp can easily be attached in the later work steps.

Step 4/4

Mind the parallelism when modifying the foot piece. Modify the heel, the rolling-off area and the forefoot area parallel to the axis/axes.

Mounting the Assembly/Lamination Dummies

Step 1/5

Mount the system joint to the holder in the positive cast in accordance to the exploded view drawing by using the assembly/lamination dummy.
Note: You can find exploded view drawings in our catalogue System Joints and Articulated System Side Bars.

Step 2/5

Take the middle of the lower leg as guidance and adjust the system case accordingly. Fix this alignment by connecting the joint retainer to the holder.

Step 3/5

Place the system ankle joint. Keep some distance to the positive cast to have enough space for the dummy for the padding material and the laminate later on. Fix the system ankle joint with a superglue.
Note: Mind the safety data sheet when using fast-acting adhesive.
Optional bilateral AFO: Make a note of the medio-lateral measurement so that you can adjust the round material accordingly in the next steps.

Step 4/5

Place the system joint with mounted holder into the positive cast and check the alignment. Fix the holder with a superglue.
Note: Mind the safety data sheet when using fast-acting adhesive.
Optional bilateral AFO: Mount the second system joint. Take care to keep the same distance to the positive cast on both sides.

Step 5/5

For a unilaterally mounted system joint, fill the second hole (without holder) of the positive cast with plaster.
Note: Stuff the hole with paper before you fill it with plaster in order to be able to easily remove the holder of the system joint later on.

Designing the Orthosis’ Edges

Step 1/5

Mark the later course of the orthosis' edges along the foot piece on the positive cast. Use the blue line for a partially flexible foot piece and the green line for a rigid foot piece.

Step 2/5

Mark the later course of the edges of the AFO with partially flexible foot piece on the positive cast.

Step 3/5

Demount the system joints. Apply plaster around the holder to avoid sharp edges that could possibly damage the film tubes subsequently.

Step 4/5

Pull a PA reinforcement stocking over the positive cast. It should fit tightly. Using hot-melt adhesive, stick cords of natural fibre (approx. 6–8mm diameter) along the marked edges of the PA reinforcement stocking.

Step 5/5

Finished positive cast
View: lateral, anterior, medial, posterior

Applying the Padding Material Dummy

Step 1/3

Heat the dummy for the padding material to 130°C and pull it over the positive cast. Cut the dummy for the padding material and remove it from the positive cast afterwards. Grind the dummy for the padding material. Then, fix it on the positive cast by using a stapler.
Note: Use a material with a proper shore hardness so that the orthosis fits well and not too tightly on the leg later on.

Step 2/3

Detailed view: joint retainer in the positive cast

Step 3/3

Finished positive cast with dummy for the padding material

Alignment of the Orthosis

Step 1/1

The alignment of the orthosis is based on the individual, gait-related normal posture of the patient. In mid stance, this results in a gait pattern that is as physiological as possible.

Last Update: 20 November 2020

 


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