Hello Stanley,
I have to concur with Kevin and Eric that kinetics (=kinematics or
movement plus dynamics or the interplay of the acting forces) are
the essence of the play in biomechanical world.
Most of us are trained to look at movement (and the resulting
position), but research is more and more pointing to the importance
of understanding how forces and force moments affect the function of
lower joints. Most of the times orthotic correction does not result
in a significant change of motion or position, but rather in
dynamics. The problem is that dynamics (forces and pressures) are
very difficult to estimate by eye or by conventional video while
motion and position can be well appreciated by rather simple means.
But in the future of podiatric practice, in my view, it will be
compulsory to use some advanced technology in order to observe and
understand the dynamics of the game. One cannot ignore that
mechanical overload and resulting injuries , most of the times, are
not due to excessive motion or position by itself, but rather to
excessive stress (loading forces) on the soft tissues (tendons,
ligaments etc...) and also on the bony contact areas of the joint.
Today I had a nice example where an orthotic correction will
alleviate pain without necessarily affecting motion.
A patient with an excessive plantar flexed 1st ray (7mm) showed
excessive reaction of her peroneus longus, enough to keep the
calcaneus in a more or less vertical position, but at the cost of
chronic pains. Inserting a everting valgus wedge did not
necessarily push the calcaneus in a more everted position, but it
will help the peroneus to balance the inverting action from to
plantar flexed 1st ray. So the net result is no real change in
position, but balancing all moments of force to net zero requires
less force of the peroneus as the valgus wedge is taking over part of
the load. So the overloaded peroneus may feel more relaxed now and
the pain subdued.
So if one looks to position only , one is likely to miss the point.
But fortunately, the happy patient will not care how it worked and
consider you still to be a good podiatrist.
My two pence ...
Well, rest me to lay may brain asleep before early morning is catching up.
Good night,
Bart
>Hello Kevin,
>
>I am glad to see that you are well. You have been missed.
>
>
>At 08:30 PM 1/23/05 -0800, you wrote:
>>Stanley, Eric and Colleagues:
>>
>>Stanley wrote in response to Eric:
>>
>><<So you believe that people walk around maximally pronated to prevent ankle
>>sprains. You also believe maximally pronated is not bad. You have mentioned
>>that since 60-99% of the population is maximally pronated, it is normal, so
>>we shouldn't treat it. Now I understand why you are content in making
>>orthotics that do change the moments and not the maximally pronated
>>position.>>
>>
>>Kevin responds:
>>
>>Foot orthoses alter the location, magnitude and temporal patterns of
>>reaction forces acting on the plantar foot. In so doing, they will alter
>>the moments acting across the subtalar joint (STJ), midtarsal joint (MTJ)
>>and other joints of the foot and ankle. In order for the orthosis to take
>>a foot out of the maximally pronated position of the STJ, they **must**
>>cause an increase in STJ supination moment. However, not all orthoses
>>that cause an increase in magnitude of STJ supination moment will cause
>>the STJ to supinate out of its maximally pronated position. Individuals
>>that understand the concept of STJ rotational equilibrium and STJ kinetics
>>will easily understand this fact.
>
>
>Kevin, this sounds wonderful, so tell me how you measure the moments that
>you change on the STJ and MTJ and the other joints of the foot (Lis
>Franc's, I assume) and the ankle with and without orthotics?
>Eric already explained the nutcracker theory. I still think it is better if
>you get the nut.
>
>>
>>Just because a clinician doesn't know what a moment is and how their foot
>>orthoses affect the moments across the STJ, MTJ and other joints of the
>>foot and ankle, this doesn't mean that these moments aren't changed by use
>>of their foot orthoses. You will find few, if any, references to STJ
>>moments (i.e. torques) before 1987 in the podiatric medical literature,
>>not because these moments weren't present in the human population before
>>1987, but because podiatrists didn't understand the mechanical
>>significance of moments, rotational equilibrium and kinetics.
>
>
>By the way, I wrote an article for Current Podiatry in 1976. In it, I
>mentioned the pronatory torque at heel contact (using Plato Schwartz as a
>reference). I can see the significance at heel contact. But it seems to be
>more like window dressing at midstance.
>
>>Now, there are an increasing number of podiatrists who understand foot
>>mechanics throughout the world with much more clarity since they
>>understand why it is so important to discuss moments acting across joint
>>axes, and not just discuss position and motion as was taught in the
>>earlier days of podiatric biomechanics. This discussion of moments that
>>we are having in this forum, is not a fad, it has replaced and is
>>replacing the older ways that podiatric biomechanics is being taught
>>around the world because it is more biomechanically accurate and explains
>>the mechanical etiology of pathologies with much greater clarity than
>>could have been explained before.
>
>Kevin, I am not sure you can say the concept of moments is replacing
>position and motion. It seems that the only additional information that can
>be gotten from moments is when there is no movement. This is why the
>maximally pronated position is so important to you. It is at this position,
>that you can analyze the situation with greater clarity. Those that look at
>position, will try to move the foot away from this. For instance, sinus
>tarsitis (your favorite condition). You will look at the decrease in
>moments at this maximally pronated position and be able to determine that
>there is 50% less force of the talus hitting the calcaneus. I, on the other
>hand in my simple approach would say that the talus should not hit the
>calcaneus, so we should move it a few degrees away from maximally pronated.
>This way there will be 0 force. At this point we do not have to make
>calculations as to how much we have to decrease the force to make the
>patient asymptomatic. I would be spending my time looking at the equinus
>that is the main causative factor, and by the position of the foot know how
>much of a heel lift is required to eliminate this extrinsic factor, so my
>orthotics can supinate the foot.
>
>>
>>Stanley also responded to Eric:
>>
>><<The difference between kinetics and kinematics, is you can change the
>>moment without effecting movement. To me, it seems like a lot of
>>superfluous information, and the more information that is not important,
>>the more confusing it becomes. Your point is that what I consider
>>unimportant, you consider to be very important. This is because you are
>>comfortable with a patient that is maximally pronated.>>
>>Kevin responds:
>>
>>Understanding kinetics is crucial to understanding the production of
>>mechanical pathology in the foot and lower extremity. Kinematics is also
>>important but kinematics does not have the potential to explain mechanical
>>pathology since it does not include a discussion of forces or moments
>>(forces and moments are the things that actually produce mechanical
>>pathology in the foot and lower extremity, not motion or lack of
>>motion). Kinetics is only "superfluous information" if you don't need to
>>understand (1) how a mechanical pathology is produced, (2) how one may
>>best treat that pathology and (3) why certain mechanical interventions
>>work better than others. Personally, I have kinetics during my
>>Biomechanics Fellowship and afterwards so I could better understand #1-3.
>
>Clinically, when we talk about the Q angle, we are talking about position.
>When we talk about SI dysfunction, we are talking about position. When we
>are talking about leg length, we are talking about position. When most of
>podiatry talks about the foot, they are talking about position. When you
>talk about the foot, you are talking moments. It would seem to me that
>moments is the exception, not the rule when we talk about pathology. There
>are times that I will talk about the forces causing pathology, for instance
>how an equinus causes a posterior displacement of the center of gravity,
>and how this increases the tension to at heel off. But the bottom line is
>that I use dorsiflexion range of motion to determine my treatment, not
>moments.
>I think you need to explain how you measure these moments, and how this is
>used to treat a foot. I have read about the two finger push up test, is
>this what you use? Do you quantify it? Or go by feel?
>
>>
>>On another note, feet that are maximally pronated at the STJ are very
>>common. However, I don't know of any research that suggests that over 50
>>% of the population is maximally pronated at the STJ. You must remember,
>>unless you are measuring the asymptomatic population and not just those
>>that come into your office for treatment, you will probably overestimate
>>the number of maximally pronated feet in the human population. However, I
>>do think that over 50% of the population is within 2 degrees of being
>>maximally pronated at the STJ. Not all these maximally pronated feet are
>>symptomatic and not all of these patients require treatment.
>>
>>I hope that no podiatrist recommends treatment for asymptomatic patients
>>simply because they are maximally pronated at the STJ. One must remember
>>that maximally pronated feet may also have symptoms (e.g. lateral ankle
>>instability) caused by excessive STJ supination moments.
>
>I don't think any knowledgeable podiatrist will recommend treatment for
>asymptomatic patients. Regarding ankle sprains, you say that on maximally
>pronated feet, there is a supination moment that causes it. I can see if
>the moments are different at different parts of the gait cycle, but
>otherwise this is contradictory. I was wondering if you are familiar with
>Articular Deafferentiation as the etiology for chronic ankle sprains.
>
>Moments, like anything new, seems like it is the entire answer, and as time
>goes on, it eventually finds its proper place. I think it is good to
>explain some of the pathology, but clinically, in midstance position,
>movement seems more important.
>
>Respectfully,
>
>Stanley
>
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Bart Van Gheluwe
Laboratory of Biomechanics
Vrije Universiteit Brussel -Fac. LK
Vakgroep BIOM
Pleinlaan 2, 1050 Brussel, Belgium
Tel.: 02/629.27.33 (31)
Fax: 02/629.27.36
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