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Friday, May 28, 2021

Negative Cast Pouring Position: 3 Typical Scenarios

This evening I am pouring plaster of Paris liquid into the negative cast to make a positive cast. Tomorrow I will begin the process of correcting that positive to a shape I desire to help with the patient’s pronation pattern. I have 5 pairs of casts to deal with this weekend, and this left foot, shown in 3 possible positions, is my most pronated foot of the 10. The RCSP, or resting heel position, in the patient is 12 degrees everted to the ground. The forefoot to rear foot measurement during my examination was over 10 degrees fore foot varus. The first method of cast correction is an ASIS correction. Therefore, you pour the cast at this 12 degree everted position. Although this is a very pronated subluxed position, it is assumed the foot pronates even further when standing. You are pouring, or correcting, this foot in a position of severely pronated, but you are not attempting to create a new arch (sometimes a great challenge), and you are stabilizing this foot with arch re-enforcement, deep heel cups, posts to add motion and stability, etc. This is a viable method especially with shoe fit issues, or previous arch intolerance. More in later posts. 

This same foot can be poured vertical, the classic Root technique, attempting a 12 degree change (12 degree everted to vertical). Of course this does not happen, but the orthotic made off this Root Balanced device, will be be changing and stabilizing the foot. I typically found a great need for orthotic adjustments with dispensed these for this foot, as the force of correction was too much in the soft tissue of the arch and forefoot. I began expert in making them comfortable with compromise, thus needing a new orthotic within the year as the forefoot varus (supinatus) begun less. Again, more in a later post. 

Here, this same left foot, which stands 12 degrees everted in resting position, is being poured at 20 degrees inverted to make the Inverted Orthotic Technique. With this technique, the arch is filled in to not block first ray plantar flexion vital for propulsion (per Dr Dananberg). 20 degree correction will typically change the heel valgus position from 12 everted to 8 everted. All the other good orthotic device stability measures: plastic thickness, deep heel cups, full shoe width, zero post motion, all help in making this a very stable device. Again, more in a later post. 

     Here I summarize 3 orthotic negative cast pouring positions that I have used to help with pronatory symptoms and stability. 3 different pouring positions from the lab are used for this severely pronated left foot where the fore foot varus equals the RCSP (not an uncommon issue). I propose that good/great stability to the foot will be accomplished by all techniques. I recommend re-casting a foot like this 6 months to a year after dispensing the orthotic devices (you should get a reduction in fore foot varus angulation). I firmly believe that if I can produce angular change (say 12 degrees everted resting position towards a vertical heel), overall the patient will be better off unless they have rearfoot valgus (like genu valgum). 

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