Letters | Thickness of Soft Casts

Your article, “Spotlight on Casting” (Winter / January 2008 Dafo Dynamics), mentions that casts made with 3M® ScotchCasts® are too flexible and won’t hold their shape.

The soft cast material, used properly, holds its shape for plaster filling and orthosis fabrication. The material needs to be five to six layers thick to do this. The instep and heel areas need to be particularly thick. One or two layers won’t produce an acceptable cast.

A soft cast is much easier to remove (using scissors) and much calmer for young patients. More rigid materials take longer to remove and require cutting tools that scare patients, such as a cast saw. Other children in the waiting room who hear cast saws are not going to be calm when it’s their turn. Thus they are more excited, and higher tone kicks in.

We use the soft cast material daily and, when used properly, it gives us no problems in producing positive mold models.

Mark K. Taylor, MLS, CPO, FAAOP
Director of Clinical and Technical Services
University of Michigan O&P Center

Thanks for writing to clarify coverage required. Your information on soft casts is a valuable testament: if five or six layers of soft cast are used, the cast holds its shape well. Unfortunately, most of the soft casts we receive are only a layer or two thick. The heel area is the most common minimally-covered spot.

Our primary concern with a cast is that it has integrity: that it holds its shape. Soft casts only a layer or two thick would tend to “puddle” when filled with plaster. This is why we need to re-wrap them with fiberglass tape.
Cast saws can be noisy and frightening to young children. When Cascade orthotists make casts, they eliminate noise by using a buffer strip and a hook-blade knife (a utility knife with a hooked blade). It cuts just fine through fiberglass tape, even at the instep, where the cast tends to be thicker. A little wiggling and “walking” the blade slowly through the curve does the trick. A sharp blade is also key. Another important factor when using fiberglass tape is the timing of cast removal. It’s best to take it off just after it hardens but before it gets rock hard.

Fiberglass casting tape offers a significant benefit: its ability to push into the cavities around boney prominences as it reaches a plastic stage just before removal, making a very precise shape of the foot and ankle.

Those practitioners with a good functional understanding of soft cast material obtain satisfactory results. Five or six layers make it work.

-- Dennis Imhof and Tom Escovar, Cascade Dafo, Inc.