Dear Biomch-l,

Thanks for the feedback regarding pronation. Here is a summary of all
the responses. Sorry for the delay.Jason Agosta.

>Hi,
>
>I am a MSc student and a Podiatrist from Olympic Park Sports Medicine
>Centre in Melbourne.
>
>Recently I was asked a question (and now will give a presentation),'How
>much pronation of the foot is too much?'. My answer was, that there are
>varying degrees of pronation among individuals as this is related to the
>alignment of a person's own biomechanics and that everybody adapts to
>their own biomechanics. Further to this, I mentioned that adaptation is
>underestimated as many people present with large ranges of motion but
>have no history of injury.
>
>I am interested in other people's response to this question.
>
>Thank you in advance,
>
>Jason Agosta
>jasonic@ozemail.com.au

From:
kgholt@bu.edu (Kenneth G. Holt)
To:
jasonic@ozemail.com.au


I think you gave a good answer to the wrong question. To elaborate on
that
answer further we must consider in more depth the actual biomechanics
involved as they relate to anatomical structure of the foot and lower
extremity. Excessive pronation is but one 'symptom' of a structural
abnormality (e.g. forefoot varus, rearfoot varus in non-weight bearing)
subject to biomechanical torques when the foot contacts the ground. For
example a foot that has a combined forefoot varus and rearfoot varus
abnormality makes ground contact in a more supinated position, leading
to a
longer moment arm and increased torque as the foot rotates around the
subtalar, transverse-tarsal, and talocalcaneal-navicular axes. This
may
lead to excessive stresses on medial tissues (e.g. post tib, plantar
fascia) and potentially cause injury to them. There may be no
'excessive'
pronation at all, and/or the breakdown of medial tissues may lead to
excessive pronation. Another potential scenario: ground contact of the
forefoot may take longer because it has a greater range of motion to
move
through. This may result in late pronation (again not necessarily
excessive) that may disrupt the normal functioning of pronation and knee
flexion, perhaps resulting in patello-femoral pain.

One must also take into account other risks that are associated with
potential injury and intensify any structural/biomechanical problems
(e.g.
obesity, exercise patterns, prior traumatic injury etc...).

There are a number of other causes for common non-traumatic injury (e.g.
bunions, ankle sprains, hammer toes, shin splints, achilles tendinitis)
due to the combined effects of structural abnormality, anatomic function
and biomechanical factors on ground contact without excessive pronation.
The major excess in pronation is the use of the term. I would refer you
to:

Holt, KG., & Hamill, J. 1995. "Running Injuries and Treatment: A
Dynamic
Approach." In G.J. Sanmarco (Ed.) Rehabilitation of the Foot and
Ankle.
Mosby

As an aside, I would argue that those who prescribe orthoses without
understanding these important relationships are illserving their
patients,
and giving orthoses a bad name when they are inappropriately prescribed
as
a result.

From:
Ned Frederick
To:
jasonic@ozemail.com.au
References:
1


My asking the question as I did, "What defines too much ?", was an
attempt
to get at a problem with your request. When you ask how much pronation
is
too much you imply that there is something intrinsically bad about
pronation beyond a certain level... but you don't tell us what! I can
assume from your podiatry training that you are refering to overuse
injuries either caused or exaccerbated by excessive pronation. I think
you'll find that many scientists , myself included, are skeptical about
that link.
Until we can prove that there is a direct cause and effect
relationship between pronation and a particular injury, and until you
define what that injury is then your question will be a tautology.
Let me give you an example. If medial ankle sprains were the
undesired result, then you would get a different value for "excessive"
pronation or calcaneal eversion than you would if patellofemoral syndrom
were the undesired result.
We both know that pronation is good and desireable for many
reasons. So, what is the outcome you are trying to avoid by limiting
pronation (or defining a limit)?

>Hi Ned,
>
>Thank you for your response regarding pronation. Your question of "What
>defines too much?", is exactly what I was getting at. Answering the 'How
>much is too much' question I mentioned that all people for different
>reasons present with varying degrees of motion and that this may or may
>not be relevant to injury.
>
>Regards, Jason Agosta

From:
Irene S McClay
To:
Nicky & Jason


Hello,

There are two ways to describe excessive pronation. The first is based
upon the mean and sd found in the normal population and determining some
criteria (ie. 1 or 2 sd above the mean) that defines excessive. Now
excessive
pronation does not always result in problems/injury. And often subjects
with injury exhibit normal pronation values. The other way to describe
excessive is that amount which causes a problem (based upon person's
mechanics, structure, etc). I prefer the first definition because it is
more clearly defined. If you are 2 sd above a population mean, then you
have a basis for which to state something is excessive. If someone
exhibits 12 degrees of pronation - and is having problems - I would not
state that it was from excessive pronation. If I was sure the problem
was
related to the pronation movement - then I would state the patient was
unable to tolerate a normal amount of pronation (for whatever reason).

I also think that people need to be precise in describing where the
pronation occurs. In research, we are most often looking at rearfoot
(due
to the difficulty in accurately tracking true midfoot motion. Midfoot
motion is typically assessed subjectively. Therefore a person could
have
12 deg (a normal amount) of rearfoot eversion, but be collapsing in the
midfoot region (which would be excessive midfoot pronation). So their
problems would be related to excessive midfoot pronation in the presence
of normal rearfoot pronation. Thus - further confusion.

This would be a great topic for the Foot list that has recently
developed. The address is foot-l@lists.nau.edu. It would generate some
interesting discussion.

Irene McClay, PhD, PT
Motion Analysis Laboratory
305 McKinly Lab
University of Delaware
Newark, DE 19716

From:
Irene S McClay
To:
Nicky & Jason


Jason,

Why do you think that would be difficult? We did just that - collected
data on 100 runners and found a mean peak of approx. 12 deg with a sd of
approx. 4 deg.

Irene McClay
From:
Irene S McClay
To:
Nicky & Jason

Jason,

We used a sample of 100 asymptomatic runners.

Irene McClay

From:
David MacPhail
To:
jasonic@ozemail.com.au


G'day Jason,

I agree with your answer re adapation. This process is essential for
bipedal
survival. Otherwise, I doubt if we've be here to discuss the issue. I
have a
paper somewhere that supports your postion. I'll try and locate it over
the
weekend.

Cheers,
David

From:
Ned Frederick
To:
jasonic@ozemail.com.au


What defines "too much" pronation?

From:
Footform Labs
To:
"'jasonic@ozemail.com.au'"


Jason,
I agree with you completely. My theorey on this is, "if it
works, don't fix it." If a subject has no pain or problems, their
condition is normal. If a subject develops problems and orhotic therapy
is designated, I still think that the patients "normal" should be the
baseline for orthotic alterations. I developed a process called Dynamic
Plantar Modeling that provides you with a physical look at what is
"normal" for your subject. When it comes to therapy, instead of
radically positioning the foot to a textbook position and modeling it,
I prefer to model what is normal and provide the minimum alteration to
this normal anatomy for symptom relief. Chek out the Science html on my
website. www.footform.com/science.html I believe we think alike on
this subject.
Randall Barna
Pres. Footform Labs

From:
Craig Payne
To:
jasonic@ozemail.com.au

This topic has been discussed ad nauseum on the podiatry list - check
the
archives.

Kind Regards
CP

From:
"V.BALTZOPOULOS"
Organization:
ALSAGER, CREWE+ALSAGER FACULTY, MMU
To:
jasonic@ozemail.com.au


Dear Jason

I agree with your view about individual variations but furthemore
in my opinion the amount of pronation may be not as critical as
when it occurs in the stance phase. Even "normal" degree of pronation
occuring late in the stance phase is likely to cause
excessive internal tibial rotation that will affect pattelo-femoral
mechanics.
I hope this view helps the debate on how much is too much pronation?

V. Baltzopoulos

Biomechanics Group
Manchester Metropolitan University