Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Everything that you are ever going to want to know about running shoes: Running Shoes Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
  2. Have you considered the Critical Thinking and Skeptical Boot Camp, for taking it to the next level? See here for more.
    Dismiss Notice
  3. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

Medial Arch Fill In to Positive Casts

Discussion in 'Biomechanics, Sports and Foot orthoses' started by t5christie, Oct 9, 2008.

  1. t5christie

    t5christie Member

    Members do not see these Ads. Sign Up.
    I'm a student and I'm a bit confused with a step in the positive cast preparation. I'm sure this is very fundamental: What is functional purpose of the medial arch fill in?

    This plaster addition obviously alters the height of the medial longitudinal arch, however how does the height of the orthotic's medial arch affect the midtarsal joints? I'm guessing that a small medial arch fill in (say 1/8) will decrease midtarsal joint range of motion due to the STJ supinatory moment that an increased arch height would impart.

    A quick explanation from someone in the know would be appreciated.
  2. Graham

    Graham RIP

    This depends on what you are trying to do with the orthoses. With a conventional "arch Support" you would have minimal arch fill to allow the orthoses to physically support the arch. However, you have to decide if the arch is actually falling in stance or if the first ray is being pushed by the ground dorsally. If the subject has an obvious plantar flexed first ray then when standing on a hard flat surface the ground will dorsally displace the distal end of the ray to the same level as the lesser metatarsals. You can do this in the non weight bearing assessment and see the arch apparently flattening. In this case the less arch fill used will support this dorsally displaced position and limit hallux extension into propulsion.

    As a sagittal guy I nearly always maximally fill the arch adding an FHL/first ray cut away to allow first ray plantar flexion and iniating hallux extension. For feet with obvious mid tarsal instability I'll throw in a medial heel skive and deeper heel cup.

    Hope this helps
  3. Admin2

    Admin2 Administrator Staff Member

  4. efuller

    efuller MVP

    Welcome Christie,

    The purpose of the medial expansion is to prevent pain. If you stand with your foot hanging over the enge of a piece of plastic it hurts right at the edge. The purpose of the expansion is to flare the edge of the orthotic away from the foot. Jeff Root gave that back in 1984 at CCPM. That is true if you use the classic Root approach which is minimal fill. If you use minimal fill the arch of the device will often be uncomfortably high and labs realized this and started using more arch fill to make the arch height easier to tolerate.

    As an aside the oblique and longitudenal axis of the MTJ are fictional conveniences. (Sorry Craig, for bothching the quote.) An axis of a joint is an imaginary line that describes motion and not a rigid hinge. The motion of the joint determines the axis and not vice versa. You can move a midtarsal joint in pure dorsiflexion plantarflexion. It is best to consider the MTJ as a planar joint with an infinite number of possible axes of motion.


  5. t5christie

    t5christie Member

    Thanks Eric and Graham. Your explanations make sense. I thought i'd fabricate a moulded orthotic from a positive cast with NO medial arch fill. I tried it on for a while but couldn't withstand wearing them. I've now realised first hand what you guys were talking about: medial arch fills do prevent pain!
  6. Welcome to Sole Support orthoses! No medial arch fill....lots of discomfort...but biomechanically correct....or so the company says!:bang:

Share This Page