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Help needed interpreting Navicular drop & drift measurements?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Berms, Mar 10, 2009.

  1. Berms

    Berms Active Member


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    I am just looking for a little more insight into the benefits of these clinical measurements.

    Now that I have added these two measurements to my clinical Biomechanical Exam, how exactly do I interpret these measurements? And more importantly, how do they influence my orthotic prescription?

    Any advice or information is appreciated.
     
  2. Craig Payne

    Craig Payne Moderator

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    They generally tend to be somewhat unreliable, so my preference is to just look at the marks on the paper to see if navicular drift is about equal to navicular drop --- the assumption is that they should be about the same (give or take a bit).

    If navicular drop > drift --> midfoot compensation mostly in the sagittal plane (ie arch collapse or low forefoot dorsiflexion stiffness) --> treat with arch support
    If navicular drift > drop --> midfoot compensation mostly in the transverse plane (ie medial midfoot bulging) --> treat with things up the side of the foot (ie medial/lateral flanges; Blake inverted device; wider orthotic; UCBL) or refer them to your enemies.

    Its not that necessary to measure it - you can see it during gait (ie what plane is compensation mostly in .... assuming you beleive in the ' motion' paradigm)
     
  3. Berms

    Berms Active Member

    Thanks Craig, what do you mean by "arch support"...... Podiatrists don't use arch supports! :D
     
  4. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    Lets call it " more midfoot support"

    Think about it intuitively .... if most of the midfoot compensation is in the sagittal plane, that is the arch collapsing (or the more appropriate terminology of low dorsiflexion stifness of the forefoot) .... then the way to stop that motion is to put something under the foot to block it (ie more "midfoot support"/"arch support").

    If most of the motion is in the transverse plane (ie high navicular drift), then the chances of something under the foot influencing that motion is significantly lower (hence the need for things up the sides of the foot).
     
  5. Berms

    Berms Active Member

    Thanks Craig, that makes sense.
     
  6. Craig Payne

    Craig Payne Moderator

    Articles:
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    One more thing on navicular drop is that Brody (Brody, DM. Techniques in the evaluation and treatment of the injured runner. Orthop Clin North Am. 1982 Jul;13(3):541–558.) made a statement that anything more then 1 cm of navicular drop is a pronated foot. He has been quoted so many times on this that I have lost count and its has almost become gospel .... anyone with a big foot will have >1cm and anyone with a small foot will have <1 cm ... duh?
     
  7. Craig Payne

    Craig Payne Moderator

    Articles:
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    Also, here is the key reliability paper:

    Reliability of Navicular Displacement Measurement as a Clinical Indicator of Foot Posture
    Ann Vinicombe, Anita Raspovic and Hylton B. Menz
    Journal of the American Podiatric Medical Association Volume 91 Number 5 262-268 2001
     
  8. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    Thats what I like about this test -- it makes intuitive sense.

    Many experienced clincians have known for a long time that those feet with a lot of midfoot transverse plane motion are harder to treat as they do not stay on top of an orthotic very well (ie the orthotic is under the foot and the motion is sideways). All the navicular drift/drop observation (as opposed to measurement) does is to somewhat quantify it.....very helpful to students when learning, but with experience, you can just see it.

    We used to call those feet with a lot of transverse plane motion, as the ones with a more vertical oblique axis of the midtarsal joint (this was back in the days when we believed that the midtarsal joint did actually have those two axes of motion!)
     
  9. Asher

    Asher Well-Known Member

    Hi Berms

    And make sure the patient is doing their laces up firmly. Slip-on shoes, including slipping into shoes with the laces already done up, is a compromise.

    I like using medial flanges but haven't had success using using polypropylene. I like to use 6mm PPT (sometimes more) which is adhered to an orthotic cover. I make the flange up to 3cms high rather than the token effort I get by default from the lab. Be aware that you rely on the shoe upper aroung the midfoot to actually exert a lateral-wards force.

    Rebecca
     
  10. Berms

    Berms Active Member

    Thanks, thats a great explanation. Yes, those feet with higher degree of transverse plane motion are harder to treat and once you understand why, then you understand that jacking up the arch in an attempt to get better control is not really going to help all that much.
     
  11. Berms

    Berms Active Member

    Hi Rebecca, I like your suggestion of the 6mm poron flange. The one thing that often prevents me from using flanges in a device is that the flange (polypropylene) can be a source of irritation and discomfort in some cases.
     
  12. Craig said it well. You CAN support a mostly drifting foot with something to prevent drop but its much harder.

    The example i use when i teach this is to use a door with a sprung hinge. Try to stop the door moving near the handle using a knuckle. Easy. Now try to stop it the same way near the hinge. Bloomin sore! Same force, but less movement in the latter case. That said, it can be done.

    Another way to think is to imagine the nav floating in space and moving diagonally down and across. You want to stop it, you want a flat surface directly in its way (perpendicular to the direction of travel). If you want to catch a ball you put the palm of your hand facing into the direction the ball is coming, you don't try to catch a ball coming in at 45 degrees by holding your hand facing upward!

    By the same example, I think the cover of the insole is important as well. If its slippy and the orthotic does not face the direction the nav travels in it will redirect the force rather than absorb it.

    So far as how to achieve the medial flange, firstly I'd agree with asher that footwear is vital. So far as orthotics i find the material is important.

    I have success with polyprop with insole which sit beneath the nav (cast corrected) or above it (UCBL). If they are half way up I get irritation. Same with AFO's.

    My weapon of choice here is high density EVA in a firm shoe. You can run a high medial flange as thick as the shoe will take and it rarely causes irritation because the beveled edge is flexible (unlike poly). The other option is to laminate the one on the other so you have the structure from the polyprop underneath the EVA.

    Regards
    Robert
     
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