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The 10 min Biomechanical assessment - what are the most important things to assess?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Berms, Oct 2, 2011.

  1. efuller

    efuller MVP

    So, the things that will increase tension on the medial slip of the platnar fascia are high pronation moment of the STJ, and high loads under the first ray (hallux and met). An early heel off in gait will increase the time and possibly the force under the forefoot so it too could increase grf under the first met. (See my windlass paper for reasoning on this.)

    So, you have to know the source of the pronation moment. There are some feet that the source of the pronation moment is ground reaction force. These feet will usually have a medially deviated STJ axis. There are some feet in which the source of pronation moment is the peroneal muscles. These feet usually have a laterally positioned STJ axis. So, before you add a medial heel skive, in an attempt to decrease pronation moment at the STJ, you should make sure that they have a medially deviated STJ axis. A medial heel skive, in a foot with a lateral STJ axis will increase peroneal activity and they may still have a high pronation moment. So, when I assess STJ axis position I don't get a number of degrees from the long axis of the foot, but rather is the axis on the lateral or medial side of average. I sort of look at it as way lateral, lateral, average, medial, way medial.

    To reduce loads under the first ray, I will tend to use a forefoot extension. Usually a reverse Morton's extension (sub mets 2-5). If they have a long 2nd, or a callus sub 2nd met already, I will add a forefoot valgus wedge as to not increase load sub 2. If they have a callus sub 2nd met and no eversion range of motion I will skip the extension.

    If they have an early heel off, or they seem to be choosing to shorten their stride, in response to an equinus then I will add a heel lift. So, that is sort of what you do with ankle joint range of motion. You decide whether or not to add a lift. I don't add many lifts. Some of the people who really need a lift often have a significantly small amount of fat pad under their heels. My theory on this is that they spend very little amount of time on their heels, so the fat pad is not forced to develop or spread.

    Eric
     
  2. Berms

    Berms Active Member

    Thanks Eric, very helpful explanations.
    Cheers, Berms.
     
  3. Berms

    Berms Active Member

    Thanks Mike, as always some very good reading there.

    I think my mistake in starting this thread was thinking that I could come up with a single "set" of biomechanical assessments that I would run through with each and every patient before prescribing orthoses... But as Simon said earlier, each case is usually different with different stresses on different structures therefore trying to come up with one "set" of tests for every case is probably not the best approach.
     
  4. Correct and you and probably a few hundred people have learnt something so it was a good idea for a thread.

    Tissue stress is the key.

    Diagnosis

    work backwards to detect why tissue is stressed

    Determine which treatment plan/s will work to reduce stress on tissue and if possible repair tissue.

    implement treatment plan

    obtain feedback from patient and if required alter treatment plan.

    so in reality we would have 3 sets of assessment/palpation requirements/questions.

    1. what tissue is stressed ?
    - history
    -direct palpation

    2. why is it stressed ?
    ie mechanically why is the tissue stressed - ie Peroneus Longus strain and the relation to the STJ axis as an example

    3. Tests which will change prescription variables ?
    ie Supination resistance.


    Once the answers for the above 3 questions have been made you can lay down the treatment plan to the patient.

    I always explain the treatment plan in the terms of planning a car holiday to the patient.

    1. decide where you are going

    2. work out the route and where you will stay

    3. start the drive, but be aware that roads may be under construction and you have to change the route but still keep in mind that the end goal is still the same.

    it did however get pointed out to me by a 10 year old that if you update your GPS before you start the drive your less likely to hit road construction. ;)
     
  5. :good:
    We call the "update of the GPS", "keeping up-to-date" by reading, understanding and implementing the findings of good quality research within your clinical work and through reflective practice.
     
  6. Asher

    Asher Well-Known Member


    4. Decide on prescription variables
    ie: lateral heel skive / everted forefoot or rearfoot post / high lateral arch contour / EVA fill to lateral arch.

    I like to write the whole thing out so I know my train of thought.

    Eg: large stiff anterior cavus so I will make sure lab keeps the lateral arch contour (you know how they always like to fill it in Berms) and extend rearfoot post distally on lateral side to stiffen lateral arch in an attempt to reduce work done by peroneals. I won't do a lateral heel skive because of the sometimes-painful small scar on the lateral plantar heel...

    ...or something like that.

    Its a bit over the top but I find it really helpful. Its all there in a snapshot and I can justify it to anyone in an instant.

    Rebecca
     
  7. David Smith

    David Smith Well-Known Member

    RobinP wrote
    And so what do you do when you see a large forefoot valgus that is non compliant and the pathology due is due to excessive peroneal group stress?

    Dave Smith
     
  8. Berms

    Berms Active Member

    :good: cheers Mike.
     
  9. Berms

    Berms Active Member

    Hi Rebecca, good point. I also like to write down my train of thought as I go - it helps when it comes to writing that prescription after the patient has left!
     
  10. RobinP

    RobinP Well-Known Member

    If someone has excessive peroneal group stress, the chances are that there will be residual supination moments occuring at the sub talar joint. These forces are greater than the peroneal group can physiologically withstand.

    The goal is then to assess the cause of this. If the lateral column is dorsiflexed relative to the medial column and the forefoot cannot be inverted with a reasonable amount of force then one would assume that the sub talar joint will need to supinate to allow the forefoot to be weight bearing in gait.

    Having established this, the goal will be to reduce the external supination moments. This would be done by laterally wedging the foot.

    However, my gauge as to how much is required is based more upon the maximum eversion test than the slightly arbitrary forefoot valgus measure.
    '
    The sub talar joint should be pronated, but not to its end of range as this might cause sinus tarsi syndrome. Potentially, the measurement of forefoot to rearfoot to an arbitrary sub talar neutral has every chance of creating pronation moments that are too great and cause excessive compression in the sinus tarsi.

    Robin
     
  11. RobinP

    RobinP Well-Known Member

    As has been discussed in the forefoot varus vs forefoot supinatus thread before, some believe that such observations are a pathology in themselves, others that they provide valuable information on prescribing, others that they have little value at all.

    However, what seemed to be universally accepted was that forefoot varus was considered to be a fixed or non compliant observation and forefoot supinatus, a flexible or compliant soft tissue contracture.

    Just curious why the same terminology doesn't exist about a forefoot valgus/forefoot pronatus(?)

    Perhaps it does, but I cannot remember reading anything about a forefoot pronatus anywhere. I think I have come across forefoot evertus before but much more rare;y than forefoot valgus and I cannot believe that every time forefoot valgus has been mentioned that it is with reference to a rigid /non compliant deformity.

    Robin
     
  12. efuller

    efuller MVP

    Increase pronation moment from the ground. Maximum eversion height tells you how big to make the forefoot valgus wedge. I've seen feet with huge amounts of forefoot valgus that have a very small maximum eversion height. Some of those feet had a traditional Root device made for them and they could not wear them.

    Also, you should look at STJ axis position. In my opinion the most common cause of peroneal overload is high supination moment from the ground caused by a laterally positioned STJ axis. A forefoot valgus may cause the STJ axis to be in a position that is relataively lateral. It's the location of the axis that is causing the problem.

    Eric
     
  13. efuller

    efuller MVP

    As the STJ pronates there is a tendency for increased load on the medial forefoot. This medial load is what "causes" the supinatus.

    When you measure forefoot to rearfoot relationship you are supposed to maximally evert the long axis of the midtarsal joint. So, when you do the measurement you will tend to remove any "pronatus". In the presence of supinatus, when you do the measurement you don't pull down the medial forefoot, you just load the lateral forefoot. If there really was a hinge like axis (LMTJ) the medial forefoot would move plantarly as you moved the lateral forefoot dorsally.

    The supinatus problem, or the inaccuracy of measuring forefoot to rearfoot relationship, is a big problem in Neutral position theory.

    I could go into it more, but I have to go.

    Eric
     
  14. Pod on sea

    Pod on sea Active Member

    '' Experience dictates that when a patient presents with knee pain and you focus your attention on the foot first off, more often than not you'll fail to diagnose the problem and alienate the patient in the process. ''

    ...possibly although in my experience patients want to know if their knee pain is related to foot/lower limb biomechanics and they may be seeing me because their physio/ other health practitioner has only focused on the knee, drawn a blank and sent them to me. So you would have to identify the structure affected then look more globally in the assessment. I think diagnosing the problem should be the first thing we do.
     
  15. Pod on sea

    Pod on sea Active Member

    I did Craig's excellent Bootcamp and have some queries which I'd like to float ...

    The medial/lateral forefoot loading test i.e. Foot flat on floor- force taken to dorsiflex 1st and 5th met- is this to establish high gear/low gear? Does it relate to orthotic rx, remembering that the low gear propulsion may be due to structural reasons (e.g. fused 1st mtpj) or a compensation to avoid pain e.g. sesamoiditis.
    Ditto re the heel lift test i.e. checking to see if the foot rolls medially or laterally when the patient lifts their heel off the floor.

    Immediate vs delayed onset of windlass- does testing this by active toe dorsiflexion with the heel on the floor actually test the windlass mechanism? Is just the windlass failing to engage if the foot pronates/arch lowers when this test is performed?
    Arrhh love it, the more I learn the more questions I have and the less I know!

    Many thanks
     
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