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Is Jacks test valid?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, Jun 30, 2011.

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    A quick thought this evening, this may have been discussed before, but I don't recall it. So....

    You know how the tension in the Achilles tendon and the tension in the plantar fascia are correlated?

    You know how we normally function in shoes which have a heel height differential?

    You know how adding a heel raise changes the result of a lunge test?

    Why do we perform a Jacks test without accounting for the heel height differential of the shoes? (or is it just me that has been doing that?)
  2. efuller

    efuller MVP

    Originally, Jack described the test to identify a "weak" medial column where when you attempt dorsiflexion of the hallux you get internal leg rotation. So in that usage I would say that is valid.

    Now, in regards to how everyone actually uses the test... Is it valid for prediction of hallux limitus or functional hallux limitus. I think that it can be if you are aware of patient muscle activation and shifts in body weight. (When you lift the toe up and let go and the toe stays up, the patient was helping you with muscular activation.)

    There are some feet where it will not be an accurate predictor of functional hallux limitus. Those feet that have a high pronation moment from the peroneal muscles in gait may exhibit signs of functional hallux limitus when there is low force required to dorsiflex the toe in jack's test.

    Is it valid when taking into acount heel lifts. Given the limitations mentioned above, a foot that has high resistance to dorsiflexion barefoot will probably have high resistance to dorsiflexion when there is a heel lift that coresponds to shoe heel height. There may be a change with heel lift, but I would bet that ranking of difficulty across feet would stay close to the same.

  3. Ranking might stay the same, but absolute stiffness will decrease. Question, when is 1st MTPJ dorsilfexion stiffness, too stiff? Assuming a delineation exists, some people will drop under the threshold due to shoe wearing.
  4. efuller

    efuller MVP

    Threshold of what? If they're in your office complaining of windlass mechanism related pain then they have crossed the threshold.

  5. Good point. I got into artificial delineation mode there for a moment like: 15 degrees hallux abductus angle or 38 degrees lunge test. You're absolutely right, Eric. Taxi for Spooner...

    Hang on a minute... I guess the threshold is subject specific, but I also guess its when the plantarflexion moment is greater than the dorsiflexion moment acting around the joint as the heel lifts the ground... So the question remains... is Jacks test valid? Moreover, is it sensitive?

    If we understand the mechanics of "windlass mechanism related pain" is there any need to perform the test at all?
  6. Boots n all

    Boots n all Well-Known Member

    Simon, heel height of a shoe will have no bearing on this at all:confused:

    However, heel "pitch" may
  7. David Smith

    David Smith Well-Known Member

    Candidate for quote of the year I think - like that, like that a lot :cool:

    Simon wrote
    Yes, two reasons, 1) to confirm our suspicions or not and so - 2) what about when the foot is very pronated and the jacks test very light?

    Boots wrote
    Are you being pedantic (or more kindly are you being precise)? By heel height Simon means heel to forefoot height differential, is this what you would call heel pitch? Raising the heel will potentially reduce Achilles tension and so reduce PF tension and so reduce plantarflexion moments on the 1st MPJ due to the tension action of the PF and so the jacks test would be lighter.

    Regards Dave
  8. Boots n all

    Boots n all Well-Known Member

    David smith
    "...Are you being pedantic (or more kindly are you being precise)?.."

    Just plain old fashioned helpful.

    ".... Simon means heel to forefoot height differential, is this what you would call heel pitch? ..."

    Correct, heel height does not equal heel pitch, you can have a 6 inch heel but if it also has a 6 inch forefoot platform we have zero heel pitch
  9. I suggest you wind your neck in, sunbeam. Read again what I wrote, I said "heel height differential" i.e the difference between the forefoot and heel height.
  10. And therein lies the problem of the false positive too.
  11. I've only ever seen internal leg rotation in one individual in response to a jack's test. This was a 20 something year old female with marked pes planus, last week. Should have filmed it.
  12. Simon and Colleagues:

    I believe the much broader question that needs to be asked is when we do our gait evaluations with the patient walking barefoot in order to more clearly see the function of the foot, are we seeing gait kinematics that may be quite different than that which is present within shoes with a 1/2" to 2" heel height differential?

    One of the smartest instructors I had in biomechanics at CCPM was John Marszalec, DPM (unfortunately he never wrote any papers and, even worse, he committed suicide in the late 1980's). John was the only one of my instructors who actually read the Journal of Biomechanics, which I was very impressed with since, at the time, I couldn't understand much that was printed in that journal. He taught me a lot about foot function during my early years that greatly helped me in my thought process at the time.

    One of the things John taught me as a fourth year podiatry student at CCPM was that if you don't see the resupination that you think you should see in late midstance during walking with the orthosis inside the patient's shoe, then add a heel lift under the orthosis and the patient will resupinate earlier. Since then, I have consistently seen that adding a heel lift to either a barefoot walker or inside a shoe will produce earlier resupination of the subtalar joint so that the kinematics of barefoot walking may be quite different than the kinematics of shoe walking, just because of the heel lift effect from a shoe. Previously, I thought this effect may have been due to decreased Achilles tendon tension but, now, I believe it could also be likely due to increased hallux dorsiflexion and increased pre-load on the plantar fascia from the heel height differential of the shoe.

    Investigating this heel height differential change in walking kinematics would be a great research project for one of you eager podiatrists that is itching to get involved in some meaningful research.
  13. Admin2

    Admin2 Administrator Staff Member

  14. efuller

    efuller MVP

    I've only seen it twice. One was a podiatry student who was in a group that I was instructing in physical exam. The students probably thought I was pretty weird when I was getting excited about it.

  15. CraigT

    CraigT Well-Known Member

    Just how 'excited' were you getting Eric? :D

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