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Help with orthosis prescription please.

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Pigsney, Feb 29, 2008.

  1. Pigsney

    Pigsney Member


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    Pt with flat feet. Particularly one foot has a huge talo/navicular/cuneiform bulge that makes contact with the ground and builds up HK, which pt actually says isn't bothering them. To get to the point, I am wondering what the best type of orthotic is. I'm thinking an EVA device with a Navicular wrap, but concerned about fitting in shoe issues. Anybody have experience with this type of thing? Also thinking about padding/apperture to offload the site of HK build up. Any advice/ideas would be very muchly appreciated. THanks

    I should add Pt has quite large ROM in Rear Foot and Midfoot.
     
  2. PodAus

    PodAus Active Member

    I take it this patient has a medially deviated STJ axis and high supination resistance?

    What other observations, and what is the goal of orthotic Tx for this patient? Just the navicular HK?

    Cheers,

    Paul
     
  3. Freeman

    Freeman Active Member

    If they have an equinus, which many pes plano have, 5mm heel raise. I generally use polypro with a poron accommodation in the sweet spot (callused area) I have used hi density plastiozote shell or EV but to get support, you have to go with more volume which then becomes an issue in itself.

    Please tell us your assessment findings, ROM, and symptoms.,
    Best regards
    Freeman Churchill, Certified Pedorthist (Canada)
     
  4. Presuming we are just going for comfort...

    I'd go a shank dependant lunarsoft with a plaster mod of about 5 mm expansion arounf the bulge which i would fill with something like poron 94 or maxacaine.

    If you are looking for a more "functional" orthotic we need a lot more info.

    Regards
    Robert
     
  5. Pigsney

    Pigsney Member

    Patient has no symptoms, his wife was concerned about the "rolling in" and thus made apptment :)

    STJ resistance hard and medially deviated subtalar jt, Jacks test easy but delayed. Large ROM STJ and MTJ and no equinus.

    Goal is for comfort and also functional as there is enough ROM for correction. PT is about late 40's early 50's, and is very active and has no symptoms now, and want to prolong this.

    I am more concerned about what material and what kind of a "flange" to use to accomodate the "bulge" and about shoe fitting issues.
    Thanks for your responses, I have a few ideas now. What is "shank dependant" lunarsoft by the way?
     
  6. David Smith

    David Smith Well-Known Member

    Pigsney

    Shank dependant is a category of orthosis type where there are 2 catergories. Shank independent and shank dependent. The shank of the shoe is that part of the sole from heel to met heads and should traditionally add stiffness to the dorsiflexion of the midfoot and often includes a steel reinforcement.

    The material of an EVA or foam type (lunasoft) orthosis is anisotropic and has a low youngs modulus in tension but a relatively high modulus in compression. IE it is very flexible when bending it.
    Therefore this type of orthosis does not significantly increase the dorsiflexion stifness of the midfoot. It therefore relies on the shoe shank to give it this stiffnes and is therefore known as shank dependent.

    A polyprop / thermoplastic shell type orthosis is isotropic and therefore has a high youngs modulus in all directions and so has a high resistance to bending. It therefore does not need to rely on the shank of the shoe to increase midfoot dorsiflexion stiffnes. (although the shoe stiffness will be addative to the overall stiffness) and so it is said to be shank independent.


    The patient has no symptoms but has signs of patholgy. You have made the perfectly reasonable decision that orthoses are required for accomodation and comfort 'plus change of function thru correction of pronation'.

    Does he need 'correction' or would accomodation be sufficient?

    With a man of this age and with the signs that you have noted, have you considered a neurological complaint such as CMT Charcot Marie Tooth.

    Does he have no symptoms because his feet are numb ?

    Does he have an progressive arthritic condition?

    Can you confidently predict long term outcome in this case?

    If he is to have orthoses then it sounds like he definently needs something soft and accomodative as described by Robert.


    Soft and accomodative, ooh sounds like my easy chair. Its lunch time and I could just do with forty winks.:empathy:



    All the best :drinks Dave
     
  7. PodAus

    PodAus Active Member

    Does active or passive modification of the Rear foot position during WB / stance significantly reduce the prominence of the 'bulge', which is so elegently referred to?

    If so, focusing the devices control on the RF may be the key, rather than 'lesion accomodation'.

    Cheers,

    Paul
     
  8. efuller

    efuller MVP

    Questions to ask:

    What kind of shoes do you want this to fit into?

    Is the talo navicular bulge plantar as well as medial?

    You can't do a shank dependent device if the patient is going to wear several different kinds of shoes. (Different shaped shanks) Also, for this patient the orthosis should be wide. The part of the shoe that the orthotic will rest on will be narrower than the orthotic. (Remove the sock liner from the next 10 shoes you see.) The orthotic will have to be supported by more than shank of the shoe. The medial portion of the orthotic will have to supported by the upper of the shoe which will also be quite variable from shoe to shoe.

    A rigid orthosis with an accommodation for plantar bony prominences could be used. However, you should plan to spend some time with a heat gun if you don't get it right the first time.

    It's not an easy question. It's tempting to just put a varus heel wedge in. Sometimes the orthotics for these people look like a flat piece of plastic except for the heel where there is a varus wedge heel cup. It might save you a lot of time grinding and heating to just do the varus wedge.

    Regards,

    Eric
     
  9. The best orthosis for this type of foot is usually no orthosis. John Weed, DPM, called this type of foot a "fully compensated rearfoot valgus". Dr. Weed taught that any attempt to support the arch in this foot will generally be less comfortable for the patient than just replacing any attempts at arch support with a flat insole. I agree with Dr. Weed and, in my experience, these patients generally do better with just a flat, cushioned insole inside their shoe with all arch supporting material removed from the shoe.

    The biomechanics of this rather unusual foot is fairly interesting and instructive for those who want to understand what the internal and external forces acting within and on the foot are and how they can cause pain and pathology. Once the talo-navicular joint area of the foot makes ground contact, then this significantly stabilizes the foot since, now, a tripod is formed with the three "legs" of the tripod consisting of the plantar calcaneus, plantar metatarsal heads, and plantar talo-navicular joint. The plantar ligaments and plantar fascia have little stretching forces on them since the ground acts as the patient's orthosis in this type of foot.

    These patients can't run and play sports very well, but they can stand and walk at a fairly normal pace with surprising ease with often no symptoms, but do tend to form some pretty good plantar-medial arch calluses over time. The great apes (Hominidae), such as chimpanzees, orangutans and gorillas, have foot structures and weightbearing talo-navicular joints in their feet very similar to these types of individuals. Dudley Morton based his ideas on short first metatarsals in the human foot on the foot structure of these species (Morton DJ: Evolution of the Longitudinal Arch of the Human Foot. JBJS, 6:56-90, 1924.) Please read the classic article of Morton's from 84 years ago that I have attached.

    This is one example of where having a lower medial longitudinal arch causes fewer symptoms, causes less pain due to tensile forces in the plantar arch ligaments and plantar muscles, and increases the overall stability of the foot. However, feet with very low arches that are not quite yet resting on the ground tend to have many more symptoms than feet where the medial longitudinal arch is firmly resting on the tround. When the arch hasn't quite reached the ground, there exist much larger magnitudes of tensile forces within the supporting plantar ligaments and muscles of the medial longitudinal arch that are required to keep the medial longitudinal arches from contacting the ground.

    Fascinating subject!
     
  10. PodAus

    PodAus Active Member

    A simple RF skive?
     
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