Casting

Casting is an essential part of any orthotic technology or lab that you will use. The purpose of this section is to compare the traditional plaster strip or slipper type cast to the newer foam casting kits that many practitioners are now using.

Slipper casts

People who still do slipper casts tend to be rather passionate about the reasons why they in fact stick with plaster. The following is based on my own personal experience both casting patients and personally fabricating literally tens of thousands of orthotics over the years.     

Advantages of plaster bandages:

1. Detail.  As a DPM and an ABC Certified Orthotist I can tell you that hands down, plaster picks up detail as in lumps, bumps, defects, bony prominences, etc. far better than anything else that I have ever casted or worked with.  However, this advantage has in my opinion, little to no significant benefit when casting for foot orthotics as stated below. 

2. Does not readily get damaged in transit to the lab. 

Disadvantages of “slipper casts”:

1. No soft tissue expansion:  As most everyone takes a slipper cast off weight bearing, there is no soft tissue expansion. This then needs to be compensated for by your lab by widening your cast laterally and placing plaster around the heel to widen it -- so that your patient will not step down on top of the heel cup when the heel splays upon normal weight bearing. This addition of plaster obviously changes the shape of the positive which could adversely change the final shape and contours of the orthotic itself.  

2. Forefoot and Rearfoot on same plane?  Ever put a slipper cast on a flat surface and see how much it rocks?  Trying to keep the forefoot and rearfoot on the same plane while “pushing up on the fifth met head to pronate whatever joint axis you’re affecting” is not often accomplished.  Subsequently the “rocking” or wobbling slipper cast has to be “tweaked”. Or plaster is added to the metatarsal area in the form of a “met bar” to compensate for this relative twisting or tweaking of the foot on the frontal plane that was captured in slipper cast. Both of these compensations or corrections in the form of added plaster can again change the shape of the positive which could adversely change the final shape and contours of the orthotic itself.

3. Time Consuming.  The preparation takes a few minutes but additionally the time that it takes to dry on the patient’s foot takes quite a few minutes.

4. Messy.  For any who have ever done slipper casting, enough said.  

Something to think about:  With all of the “standard modifications” required to actually use a positive from a slipper cast. Is this method actually a less accurate way to cast for foot orthotics?  In my opinion, an accurate casting method wound not require any “corrections or modifications” before it can be used to fabricate an orthotic. This is true whether or not you are using a computer or scanning technology to “cast” your patients as all of these modifications and corrections are built into the software and done automatically.     

Foam Casts

Advantages of foam:

1. Allows for soft tissue expansion:  A proper foam casting technique is done by the practitioner pushing the foot down into the foam in a specific and controlled manor. When you correctly bottom the heel and the forefoot, you get appropriate amounts of soft tissue splay which of course translates directly into the positive with no added plaster required.

2. Forefoot and Rearfoot relationship:  As you have a rather obvious and consistent frame of reference, namely the bottom of the box, when you bottom out the heel and forefoot completely, by definition they are always on the same plane.  Therefore, if you properly bottom out the entire foot, you will never have any frontal plane rotation or “twist” captured in your cast as again, they will both always be on the same plane.

3. Quick: A proper foam casting technique literally takes less than two to three minutes for the entire casting process.

4. Minimal if no mess.  After you brush the few flecks of foam off your patient’s foot back into the box, the few bits that escape and hit the floor can be swept up or sucked up with a small hand held vacuum in literally a few seconds.

In my opinion, when done correctly, the foam casting method is the most accurate as it does not require any manipulation to the positive to fabricate an orthotic. 

Additionally, when done correctly, the patient’s foot ends up in what is commonly known as “sub talar joint neutral” which is a goal of slipper casting.    

Disadvantages of foam:

1. It requires a technique that does not compress or lower the arches of the foot. If you aren’t careful, you can easily obliterate the medial, lateral or transverse arches of the foot by erroneously pressing down dorsally over these various arches while bottoming out the foot in the foam. The remedy for this is to have a consistent technique that allows you to bottom out the entire foot while knowing where to press and where not to press on the dorsum of your patient’s feet. 

2. You must correctly bottom the foot or you will end up with a very inaccurate cast.  Not fully bottoming the heel and met heads will most definitely produce an inaccurate and subsequently useless cast of your patient’s foot. Again, this is remedied by correct technique.

3. They can be damaged in the mail requiring a recast. This can be almost one hundred percent prevented by packing the foam cast kit correctly. Includes placing wadded-up paper towels in the foam kit itself before you seal it and placing the kit into a protective mailing sleeve. When this is done, short of having a 400 lb pallet being set on your box by your favorite express mail carrier (which does in fact happen from time to time), you will virtually never have a problem with damage from shipping.   

Summary

From my experience fabricating literally tens of thousands of foot orthotics, there is no doubt that foam is a much easier and more accurate casting medium to work with as the resultant positive requires no additional modifications or corrections providing the foam cast was taken correctly. 

I believe that foam got a bad name from a large group of practitioners popularizing full weight bearing foam impressions for their particular brand of orthotics. Capturing the fully pronated and pathologic position of the foot is in my opinion and experience, the last thing that you would want to do but they seem to have their reasons all worked out.

I do not condone or suggest that you in fact ever take a full weight bearing foam cast. 

The point is that yes, you can take a completely horrible and useless foam cast, but there are techniques that allow you to capture a functionally “neutral” position of the foot that additionally require no modification or correction.  We in fact teach such a technique in our course “Structured BioMechanics”.       

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