Jeff, Eric and Colleagues:
Jeff wrote in reply to Eric:
<<Eric, I am all but convinced that the neutral position of the STJ is that
point in which the head of the talus reaches the bottom of the arc within
the joint socket of the talocalcaneal portion of the talocalcaneonavicular
joint. As you move the STJ the anterior and middle facets of the calcaneus
rotate about the head of the talus in the frontal plane. When the talar
head reaches the bottom of the arc, a directional change takes place because
the radius of the TC portion of the TCNJ is not constant. This creates the
distinct feel associated with the neutral position of the STJ.>>
Kevin replies:
I determine the neutral position of the subtalar joint (subtalar joint
includes the three facets of the articulations between the talus and
calcaneus) to be the point where, when loading the subtalar joint (STJ) by
using digital pressure on the plantar fifth metatarsal head and then putting
the STJ through a range of motion, there is a "flat spot" within the range
of motion of the STJ. This is the technique which was taught to me by my
biomechanics instructors at CCPM: Drs. Ron Valmassy, Chris Smith, Lester
Jones, Richard Blake, John Marszalec, and John Weed. This position has also
been described as a "position of stability within the range of motion of the
STJ" by a few of my instructors. However, over the last twenty years of
examining the STJ, when performing the above technique, I can use the
quality of the STJ range of motion to find a "flat spot" within the range of
motion of the STJ that I call "neutral position".
In the anatomical preparations which I have observed, I believe this feel of
a "flat spot" within the range of motion of the STJ which I call neutral
position is primarily caused anatomically by the attainment of maximum
congruency of the posterior facets of the talo-calcaneal joint. I first
wrote about this previously in my April 1991 Precision Intricast Newsletter
(over 10 years ago!!!!):
".......One of the greatest problems with Dr. Root's definition of STJ
neutral position is that its lack of clarity practically renders it a
useless definition. If we are to define the neutral position as a position
in which the foot is neither pronated or supinated then first we must
precisely define at what position of STJ rotation the foot becomes pronated
and at what position of STJ rotation the foot becomes supinated. It is only
when "pronated" and "supinated" are exactly defined that we could then
derive a definition for neutral position using these terms. To my
knowledge, the only way the terms "pronated" and "supinated" have been
defined has been using "neutral position" as a reference which gets us back
to the same problem of trying to define a term using undefined terminology.
The second part of the definition states that neutral position
is that place within the normal STJ range of motion at which twice as much
inversion may take place as eversion. If we use the STJ of the normal foot
as a reference then what happens to that definition when we look at the
other 99.5% of the population which does not exactly match the criteria we
have established for normalcy? In other words, when I am examining an
abnormal foot (which are the only ones I see), what criteria should I use
for neutral position of the STJ? Should I use the criteria that neutral
position is at the position of 2:1 supination to pronation? Or should I use
the position of 2.6:1 supination to pronation or maybe even a position of
1.2:1 supination to pronation as my position of neutral position?.........
(some cut.............)
The best way to define neutral subtalar joint position is to use terminology
which describes the relative positions of the facets of the calcaneus and
talus to each other. We could then determine whether the externally
measurable clinical parameters outlined above correlated with this
anatomical position of the calcaneal facets.
In spending many hours looking closely at numerous foot
skeletons, I came to the conclusion that STJ neutral position is that
position at which the articulating surfaces of the posterior facets of the
talus and calcaneus achieve maximal congruency. This position of maximal
congruency of the posterior facet of the STJ also corresponds to the
position where the "flat spot" can be felt within the range of motion of the
STJ.
What is the "flat spot" within the STJ range of motion? It is
that position within the STJ range of motion which can be felt by the
examiner only during open kinetic chain examination of the STJ by grasping
the fifth metatarsal distally, placing a constant dorsiflexion force on the
fifth metatarsal toward the patient's nose (i.e. in order to maximally
pronate and lock the oblique and longitudinal midtarsal joint axes) and
slowly putting the STJ through its range of motion. At a position from 5 to
15 degrees from the maximally pronated position of the STJ, the forefoot
will rotate through a flatter arc of motion which also can be felt by the
examiner as a position of increased stability of the forefoot to inversion
and eversion to the tibia.
The "flat spot" method of STJ neutral position determination is
one which many podiatrists use daily in the evaluation of their patients'
feet. I rarely use any other method to find STJ neutral position since the
"flat spot" method seems to correlate very closely to the other three
techniques of neutral position determination described above. It is a much
more difficult technique to teach and learn but seems to be easier to
perform and more consistent from foot to foot once learned. Hopefully,
research will be performed in the future to determine whether maximal
congruency of the posterior facet of the STJ is the true anatomical
description of STJ neutral position which Dr. Root had described many years
ago." (Kirby, Kevin A. Foot and Lower Extremity Biomechanics: A Ten Year
Collection of Precision Intricast Newsletters. Precision Intricast, Inc.,
Payson, Arizona, 1997, pp. 21-22).
I don't believe that the anterior and middle facets of the talo-calcaneal
joint play as much of a part as the posterior facet does, however, it is
certain that all of the facets must play some role in the creation of this
"flat spot" in the range of motion of the STJ .
Jeff continued:
<<How can we explain rearfoot varus and valgus with this theory? I believe
a rearfoot varus occurs when the posterior surface of the calcaneus is still
inverted when the head of the talus reaches the bottom of the arc at the TC
portion of the TCNJ. The varus torsion of the body of the calcaneus creates
a situation where the posterior heel bisection is inverted when the talus
rests in the bottom of the arc. As the STJ moves out of neutral and
pronates, the posterior heel bisection is inverted but is everting as the
STJ pronates.
In a rearfoot valgus condition, the posterior bisection of the heel would
already be everted in the frontal plane when the head of the talus rests at
the bottom of the arc at the TC portion of the TCNJ. When the STJ pronates,
the everted calcaneus would continue to evert.>>
Kevin replies:
It is this above theory which uses the posterior bisection of the calcaneus
as the reference for determining the "forefoot to rearfoot relationship",
how to balance a cast for the fabrication of foot orthoses, and whether the
calcaneus is in a "uncompensated", "partially compensated" and "fully
compensated" position which, I believe, is the "neutral position theory"
which Eric was talking about. I also would like to know of any research
which has been done in the last thirty years which has shown that these
measurements have any correlation to gait function or to pathology. All I
can remember is that Hamil et al showed no correlation between these
measurements and the dynamics of gait. It seems that if we are to put all
the theories on equal footing, then all the theories should be laid out on
the table for equal inspection to be either supported or refuted by
research. So far, even though the neutral position theories are useful
clinically, to my knowledge, they have not been supported by any research to
date. That has, however, not stopped the teachers of podiatric biomechanics
around the globe from teaching it as "fact" for at least the past two
decades. I am hoping that we will have enough research behind us within
the next decade to be able to start to see which theory of foot function has
the most support behind it. Until that time, we will all just be
theorizing, as usual.
Cheers,
Kevin
********************************************
Kevin A. Kirby, DPM
Assistant Clinical Professor of Biomechanics
California College of Podiatric Medicine
Private Practice:
2626 N Street
Sacramento, CA 95816 USA
Voice: (916) 456-4768 Fax: (916) 451-6014
E-mail: [log in to unmask]
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