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casting modifications

Discussion in 'Biomechanics, Sports and Foot orthoses' started by matthew malone, Jun 25, 2009.

  1. matthew malone

    matthew malone Active Member

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    Hi guys i hope someone can just clarify something for me.

    I saw a patient with peroneal brevis tendonopathy, they basically presented with
    a laterally deviated stj axis, pes cavus foot with plantarflexed 1st ray and on the right foot a forefoot valgus which was causing late stance supination and probably the peroneal irritation.

    My question is when taking a slipper cast to STJ neutral, when you place the cast on a flat surface it is inverted due to the forefoot valgus.

    Now i know thati want a forefoot valgus post, however when writing the script, if i ask them to balance the forefoot to heel vertical am i effectively adding a forefoot intrinsic valgus post or would you always ask for this to be done then also ask for a extrinsic forefoot valgus post. Or would you leave the +ve as is and just add an appropriate forefoot valgus post - or does it not matter??


  2. efuller

    efuller MVP

    Hi Matt,

    It depends on the lab and what the default procedure of the lab is. I suggest you call the lab you are dealing with and ask them what they would do depending on what you write.

    In addition to what you have discussed, I would ask for a top cover with extension of wither forefoot valgus wedge, or reverse Morton's extension (1/8" lift under met heads 2-5)

    It is also important to know how an intrinsic forefoot valgus post works and modifies the orthotic shell. You can place the foot in casting position and place the orthotic against the foot. The orthotic, with an intrinsic forefoot valgus post, should curve away from the distal lateral aspect of the foot.



  3. footdoctor

    footdoctor Active Member

    Hi Matt,

    Basically if you ask the lab to balance the forefoot to rearfoot you are effectively adding intrinsic forefoot valgus correction.

    Generally an Extrinsic forefoot valgus post to sulcus will be more effective here.

    Therefore I would instruct the lab to apply an extrinsic forefoot post to sulc at the degree required to bring the calcaneal bisection to vertical.Or if the deformity is excessive you could choose to apply 50% intrinsic correction and 50% extrinsic correction.

    You could instruct in degrees by measuring yourself before you send your casts to the lab.

    Place your cast on a flat level surface.

    Wedge the forefoot of the cast so that the post calc is vertical.Draw a line bisection the post calc.

    Remove the wedge and measure the angle of the post calc bisection line with a protractor/angle finder.

    Specify on the prescription form the number of degrees of extrinsic valgus posting that you require.

    Good luck.

  4. matthew malone

    matthew malone Active Member

    cheers guys thats cleared a few things up. the forefoot valgus is not excessive so i think ill get the valgus post to sulcus. I just wanted to know which post will provide more of a pronation moment and if an intrinsic post was sufficient enough.

    Thanks again for clearing things up
  5. efuller

    efuller MVP

    To increase pronation moment you want to shift the center of pressure of ground reaction force as far lateral and as far distal as possible. (This assumes that the axis is located from proximal lateral to distal medial. The higher the angle of the axis from the sagittal plane the distal foot will be a greater distance from the axis.) So, you would get a greater pronation moment by having a valgus wedge or extension which others seem to be calling a long extrinsic post. You can add a peice of cork wedge on to a top cover whether you have an intrinsic or extinsic post.



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