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Casting modifications

Discussion in 'Biomechanics, Sports and Foot orthoses' started by jkghardy, Oct 10, 2014.

  1. jkghardy

    jkghardy Welcome New Poster

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    hello; I have been doing alot of reading up on the tissue stress theory and I wanted to know what changes do you make when casting the foot. I still cast in subtalar neutral. but is this the acceptable when applying the theory. thanks
  2. efuller

    efuller MVP

    I still cast in neutral. I think that dorisflexing the lateral column to get the shape of the foot when the ligaments are loaded is still an important concept. That said, you need to think about what you want the finished orthotic to look like. Will there be an inverted or everted heel cup? Do you want an intrinsic forefoot valgus post? If you are not making the device yourself, you have to worry about communicating with person who is making it. That person may still be thinking in terms of forefoot to rearfoot relationship and heel bisections. Are you familiar with the maximum eversion height concept. (There is a thread about it here on the arena) You can choose to dorsiflex or plantar flex the first ray to alter the forefoot to rearfoot relationship to get what you want.

    Another thing that I do is have the patient stand relaxed and put my finger under the medial arch and lift a little and then measure how high the top of the finger is off of the ground. I then ask for the orthotic to be made this high. When you cast in neutral position, the arch height in the cast will be higher than it is in stance. Some people need a lot of push in their medial arch. Some people can't tolerate much push in the medial arch. The number of millimeters gives you a decent place to start in the amount of arch fill that is added to the positive cast. This is an area that is still an art.

    You can apply the principles of tissue stress orthotic design to any method of casting. I happen to use neutral position because that is what I started my experimentation with.

  3. Ray Anthony

    Ray Anthony Active Member

    Lee WC1, Lee CK, Leung AK, Hutchins SW: Is it important to position foot in subtalar joint neutral position during non-weight-bearing molding for foot orthoses? J Rehabil Res Dev. 2012;49(3):459-66.


    When taking molds for foot orthoses, it is accepted practice to position the subtalar joint in its neutral position. However, foot orthoses have no contact with the talus, and this leads to a hypothesis that as long as there is correction available to appropriately align the forefoot relative to the hindfoot when taking a mold, changes in subtalar joint angles do not lead to significant alterations in the plantar surface shapes of the molds taken. This study tested this presumption with 20 subjects between 22 and 46 years old. During non-weight-bearing casting, the subtalar joints were aligned at positions of 4° of eversion, 2° of eversion, 2° of inversion, and in neutral. At each orientation, forces were applied over the forefoot such that the metatarsal heads were aligned with the rearfoot. Digital scanning was used to analyze the shape of each negative mold. There were significant changes in projection volume in different subtalar joint orientations. However, the changes in arch heights, navicular height, and protrusion were insignificant and very small. It is therefore suggested that as long as the forefoot and hindfoot are appropriately aligned, variations in the orientation of the subtalar joint would be acceptable.
  4. Craig Payne

    Craig Payne Moderator

    You should cast the foot in the position that is needed to get the shape that you want so that the foot orthotic will have the design features to deliver the prescription variable that is needed.

    I hold the rearfoot in a variety of positions, depending on what I want to achieve. (I did one yesterday with the STJ maximally inverted and the forefoot plantarflexed on the rearfoot ... it was for a DMICS)

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