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 1/2

After the positive cast has been produced, we recommend further modification. In the following work steps, you can see the modifying process on an exemplary AFO.

Step 2/2

Stick the alignment aid through the previously marked mechanical pivot point and fill the negative cast with plaster. Let the plaster harden. The hardened plaster forms the positive cast, which is to be modified and can be seen here with correctly adjusted heel height on an h-Cast.

Reinforcing the Foot Piece

Step 1/6

Mark the 1st and 5th metatarsal bone. Determine the rolling-off line between the two markings and draw it parallely to the mechanical joint axis (auxiliary line A).

Step 2/6

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.

Step 3/6

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

Step 4/6

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 5/6

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 6/6

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 1/8

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 further exploded view drawings in our catalogue System Joints and Articulated System Side Bars.

Step 2/8

When mounting the system ankle joint, take the middle of the lower leg as guidance and adjust the system case accordingly.

Step 3/8

Align the system joint as set before. Fix this alignment by connecting the joint retainer to the holder.

Step 4/8

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 fast-acting adhesive.
Note: Mind the safety data sheet when using fast-acting adhesive.
Option bilateral AFO: Make a note of the medio-lateral measurement so that you can adjust the round material accordingly in the next steps.

Step 5/8

Optional bilateral AFO: Remove the system joint with dummy and the holder from the positive cast. Shorten the round material and check the medio-lateral measurement.

Step 6/8

Option bilateral AFO: Demount one system joint. Place the holders on an even surface, the still mounted system joint exceeding the edge, to check the proper alignment of the squares. Secure the round material in the holders.

Step 7/8

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

Step 8/8

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.

Marking the Orthosis’ Edges

Step 1/2

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, the green line for a rigid foot piece.

Step 2/2

Mark the later course of the AFO's edges on the positive cast.

Modifying the Orthosis‘ Edges

Step 1/5

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

Step 2/5

Modify the edges of the later AFO.
Note: Take care not to flange the edges too much.

Step 3/5

Detailed view: modified ankle area of the positive cast

Step 4/5

Detailed view: modified lower leg area of the positive cast

Step 5/5

Finally modified positive cast
View: lateral, anterior, medial, posterior

Applying the Padding Material Dummy

Step 1/4

Heat the dummy for the padding material to ca. 130°C (266°F) and pull it over the positive cast. Cut the dummy for the padding material appropriately and remove it from the positive cast afterwards.
Note: Use a material with a proper shore hardness so that the orthosis fits well and not too tight on the leg later on.

Step 2/4

Grind the dummy for the padding material and fix it on the positive cast by using a stapler.

Step 3/4

Detailed view: joint retainer in the positive cast

Step 4/4

Modified 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: 7 September 2020

 


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