Modifying a KAFO 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 KAFO.

 Producing the Work Basis

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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 KAFO.

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Stick the alignment aids through the already marked mechanical pivot points 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

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

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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.

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Anatomically shaped positive cast

 Preparing the Trial Shell

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Heat the trial shell material in an oven suited for plates (ca. 170°C/338°F) or an infrared oven (ca. 150°C/302°F). Wrap the heated plate around the positive cast and ensure a tight fit by vacuumising the plate. Saw out the trial shell and grind it as soon as the material has cooled.

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Have the patient try on the trial shell. Make sure the trial shell fits well at the heel area so that you can check the length and volume as well as the joint's measurements and angles. Mark the areas which may need to be adjusted at the positive cast.
Note: When using a ventral shell, you should also saw out a ventral trial piece to check how it fits.

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Hold the lower leg in the trial shell and bring the leg into maximum extension to check if an extension beyond the position set by the KAFO is possible. This is especially important for the flawless functionality of automatic knee joint systems.
Note: Please make sure the patient does not sit on the trial shell!

 Mounting the Assembly/Lamination Dummies

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

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When mounting the system knee joints/system ankle joints, take the middle of the thigh/lower leg as guidance and adjust the system cases accordingly.

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

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

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Option bilateral KAFO: Remove the system joints with dummies and the holders from the positive cast. Shorten the round material and check the medio-lateral measurement.

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Option bilateral KAFO: 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.

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

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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

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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.

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

 Modifying the Orthosis’ Edges

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

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

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Detailed view: modified ankle area of the positive cast

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Detailed view: modified lower leg area of the positive cast

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Detailed view: modified knee area of the positive cast

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Detailed view: modified thigh area of the positive cast

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

 Applying the Padding Material Dummy

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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.

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

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Detailed view: joint retainer in the positive cast

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Modified positive cast with dummy for the padding material

 Alignment of the Orthosis

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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.