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Midtarsal Joint Kinematics: Motion vs. Stiffness

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Old 12th April 2009, 05:25 PM
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Default Midtarsal Joint Kinematics: Motion vs. Stiffness

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This new thread is split off from the thread Are Root Biomechanics Dying?
Quote:
Originally Posted by Jeff Root
The spatial location of the STJ axis is like using an x-ray to confirm what you already expect to see. I'm not so sure it provides significantly more information on which to base your orthotic prescription once you know the STJ open chain ROM and once you do a visual gait analysis. I find it far more important to assess the spatial location of the MTJ axis. Those individuals with a significantly greater ratio of ad/abduction of the MTJ relative to plantar/dorsiflexion (ie a more vertically oriented MTJ axis) tend to have feet that are more difficult to control.

For example, if you see a child with a flatfoot condition but whose heel remains vertical or slightly inverted during stance, is he fully pronated at the STJ? If you look at the spatial location of his STJ axis and it is adducted or medially deviated, what does this tell us? There seems to be far greater variability in the MTJ than the STJ. The MTJ is a far more complex joint. This child might be subluxing at the MTJ during stance and may be standing with the STJ everted beyond is normal ROM when his heel is slightly inverted or vertical. That's why we need to look the open chain range of motion of the STJ and the angular relationship of the heel to leg. If I had to give up one piece of the above information about this child, it would be the spatial location of the STJ axis since it would be the least useful clinically for me when it comes to writing an orthotic prescription.

I would also want to know his open chain range of ankle joint dorsiflexion and his open chain range of dorsiflexion of the hallux more than the spatial location of the STJ axis. I know Kevin is very keen on the technique since he is the one who developed it, but when I talk to doctors about their orthotic prescriptions they rarely mention the spatial location of the STJ axis to me. In comparison, functional hallux limitus is frequently discussed and has a direct influence or the orthotic Rx (reverse Morton’s extension, Cluffy wedge, etc.).

I would be interested in hearing from other lab techs and/or owners on this forum as to what criteria they discuss with their customers when conducting prescription consultations.
Quote:
Originally Posted by Kevin Kirby
Subtalar joint (STJ) axis spatial location can give you a direct link to what the prevailing STJ pronation and supination moments acting on the foot are. STJ spatial location can also inform the clinician as to how the orthosis will need to be designed to specifically reduce the pathological internal forces which are causing the patient's symptoms, how the clinician may best optimize gait function, all without causing other symptoms or pathologies in the patient.

Recent research over the last decade has shown that the midtarsal joint (MTJ) does not have a fixed, immovable or highly constrained axis, as you suggest above (Nester CJ, Findlow A, Bowker P: Scientific approach to the axis of rotation of the midtarsal joint. JAPMA, 91(2):68-73, 2001;Nester C, Bowker P, Bowden P: Kinematics of the midtarsal joint during standing leg rotation. JAPMA, 92:77-89, 2002; Nester CJ, Findlow AH: Clinical and experimental models of the midtarsal joint. Proposed terms of reference and associated terminology. JAPMA, 96:24-31, 2006). Therefore, I don't see how you can say that somehow you can move the MTJ around to find a singular "MTJ axis" when the MTJ will move in any direction depending on the magnitude, direction and point of application of the external force being applied to it.

Motion of the midtarsal joint does not occur about a single axis or two axes as has been taught for the last 30+ years within podiatric biomechanics. The midtarsal joint, rather, has a constantly moving axis of motion that is dependent on the prevailing external forces acting across it and the prevailing internal forces acting within it from the muscles, ligaments and joint surfaces, at that instant in time. In the foot shown, the MTJ is clearly seen to be a relatively unconstrained joint; a joint that allows motion around an infinite number of moving axes, not around one or two joint axes.
Quote:
Originally Posted by Jeff Root
Kevin, I watched your video of you moving the MTJ. Unfortunately the technique you are using does not enable you to isolate motion at the MTJ. In order to better isolate MTJ motion, you need to grasp the cuboid and the navicular together as a unit. By grasping the foot so far distally (sub 5th met head), you are not only getting motion at the MTJ, but also at every joint distal to the MTJ. This makes it difficult to draw meaningful conclusions about the axes of the MTJ.

In order to better isolate the motion of the MTJ, with the patient supine, grasp the left foot with your right by placing your thumb directly plantar to the cuboid and navicular and your 2nd and 3rd fingers over the cuboid and navicular dorsally. Move the MTJ in pure ad/abduction and then in pure plantar/dorsiflexion and in pure in/eversion. Next, vary the direction of motion with respect to these planes. You will find when you better isolate the motion of the MTJ, the average MTJ demonstrates the greatest range of motion in the direction of simultaneous adduction/plantarflexion and simultaneous abduction/dorsiflexion. There is far less motion in the direction of inversion/eversion. You will not be able to clinically appreciate these motions when holding the foot as far distally as you are in the video, because you are getting motion elsewhere.

In order to help prove my point, I doubt that you would place skin markers or pins in the foot at the point you are applying forces in order to measure the relative motion of the cuboid and navicular relative to the calcaneus and the talus. You would however, place skin markers or pins directly over the cuboid and navicular, which is where I suggest you apply external forces when evaluating the MTJ. This is far more logical than your method if the goal is to isolate MTJ motion in order to draw conclusions about its role in dynamic function.

Virtually every time I teach this technique to podiatrists in clinical workshop, they ask "Why was I never taught this technique in podiatry school?". For those who are interested enough to master this technique, it can provide extremely important visual and tactile feedback to the practitioner as to the nature of an individual patient's MTJ as compared to that of others.

In some feet, there is more freedom and range of ad/abduction as compared to plantar/dorsiflexion. These are typically the feet in which the forefoot has a greater tendency to abduct on the rearfoot in stance. These are the same people you would probably describe as having an adducted or medially deviated STJ axis. In other individuals, it is difficult to produce ad/abduction at the MTJ. This is typical in a rigid, cavus foot. I find the ratio of motion at the MTJ relative to the cardinal body planes to be a very meaningful, clinical assessment tool.

I mean no personal disrespect, but I honestly doubt that you will be receptive to my recommendation. However, it is my hope that others on this forum may consider my recommendation and try to learn this technique so they can draw their own conclusions. This method of MTJ evaluation has been extremely beneficial to me and for those clinicians I know who use it regularly during their open chain examination of the foot.
Quote:
Originally Posted by Kevin Kirby
John Weed personally taught me the same technique that you have described above. So not only did I learn the technique that you described above about a quarter century ago, but I taught this same technique for many years. However, after reading Chris Nester's papers which I mentioned in my last posting which says there are no simultaneously occurring oblique and longitudinal midtarsal joint axes, after researching all the previous scientific articles on midtarsal joint biomechanics, after writing four Precision Intricast Newsletters on the subject, and after lecturing both nationally and internationally on several occasions on midtarsal joint biomechanics, I would have to disagree that the midtarsal joint examination technique does anything other than reproduce the erroneous results that were also obtained by Hicks and Manter in regards to midtarsal joint kinematics. To paraphrase Chris Nester: "It is not the axis of the midtarsal joint that determines the motion of the midtarsal joint, rather it is the motion of the midtarsal joint that determines the axis of the midtarsal joint.

Hope you and your family all have a nice Easter.
Quote:
Originally Posted by Eric Fuller
I have to disagree with you about the finding the axis to confirm what you already know. I've been surprised when looking at a foot by how wrong my first guess was when compared to palpation of the axis. There are some very high arched "rigid" feet that will have medially deviated STJ axes and there the very rare low arched, very flexible feet with a medially positioned STJ axis.

Jeff, how do you alter your prescription once you find that a MTJ is more difficult to control?

Jeff, how would you alter a prescription if you find that a STJ is maximally pronated versus not maximally pronated in stance?

I often assess this anyway to assess where the stresses in the foot are more likely to be, but use a different technique. I find the maximum eversion height in stance more satisfying in that I don't have to draw lines and do math or worry about skin lines moving between the seated bisection and stance. (Yes, you can take that into account by redoing the bisection, but I don't want to worry about it.) My reasoning is that if you want to see if the STJ is maximally pronated, see if there is range of motion when motion is attempted.

As for the usefulness of the STJ axis position: I don't see a better measure you could use to decide whether or not to add a medial heel skive, no skive, or a lateral heel skive. Jeff, do you recommend heel skives to your customers?

People will not talk about what they do not know about. Jeff, if you asked them about STJ axis position they might start using it more in their prescription writing decisions. I agree WB and NWB range of motion of the 1st MPJ can be used in prescription writing.
Quote:
Originally Posted by Jeff Root
Apply your same logic to a simpler joint, for example the 1st MPJ. A trained examiner can appreciate the relative difference in the range and direction of open chain motion at the 1st mpj. In some people, the range of dorsiflexion and plantarflexion are considerably less than others. In some people there is far more transverse plane motion than in others. By applying forces in all directions, one can see the resulting motion or lack of motion available. That motion is what determines one’s clinical appreciation of the axis.

Kevin, are you saying that there is no difference in the range and direction of motion or in the anatomical structure of one mtj as compared to another? Are you saying that I can apply a force in any direction to the mtj and get the same range and freedom of motion? I think not. I agree with Chris Nester. So when I apply a force in one direction at the mtj and get much different motion than I did when applying that same force in the same direction to other individuals, it does tell me something about the quality, range, and direction of available motion. That resulting motion is exactly what helps me appreciate the axes (note plural!)clinically. It is the totality of the applied force in various directions that allows me to differentiate one mtj from the next. I’m not saying the MTJ has one, two or ten axes. I’m saying by examining all of the available motion at the mtj and by relating the motion to the cardinal planes of the body, one appreciate and compare one mtj to another. Even in your test, if you compared the excursion of the forefoot in space and compared it to the cardinal planes of the body, you would appreciate differences from one foot to the next due to fundamental differences in their joints (ie joint axes as determined by the motion).

We have had this same discussion many times before. As I'm sure Eric Fuller can verify, I have described my rather limited and constrained MTJ motion as compared to that of others. There is nothing that you or anyone else can say to change my opinion that this is a very useful clinical technique when conducted properly, because I have seen so much benefit come from using it. Although you may not find it clinically useful, that doesn't mean that others can’t or don't.
Jeff, Eric and Colleagues:

This is one of the best discussions we have had on the midtarsal joint for some time, therefore, I have taken the liberty of creating a new thread that hopefully will be a valuable learning resource for many of those that are following along.

Jeff, I am totally in agreement with you that there is great inter-individual variability in the magnitude and quality of midtarsal joint (MTJ) motion. However, I am in disagreement with you that the examination technique you have described, the same one that John Weed, DPM, taught personally to me and I taught to other podiatrists and podiatry students for 10-15 years, is actually measuring "the axis of motion of the MTJ", or as you stated: "I find it far more important to assess the spatial location of the MTJ axis."

Instead, the examination technique you describe is a measure of MTJ stiffness, not of "the spatial location of the MTJ axis". In other words, when you perform this examination technique and find it more difficult to move the MTJ in one plane along one axis of motion rather than in another plane along another axis of motion, you are not determining "the spatial location of the MTJ axis" you are measuring the stiffness of the MTJ along each of it's many possible joint axes. You might claim that the MTJ has a vertical axis if the abduction-adduction direction of the navicular and cuboid (NC) relative to the rearfoot has the least joint stiffness. [Joint stiffness being defined as the amount of external force or external moment applied across the joint divided by the amount of joint rotation that occurs as a result of the applied external force or moment.] You might also claim that the MTJ definitely does not have a vertical axis if your applied manual force on the NC in the adduction-abduction direction produces less joint MTJ motion than when an adduction-plantarflexion and abduction-dorsiflexion external force is applied. Your examination technique rather than finding "the spatial location of the MTJ axis" is, I believe, determining the axis of motion of the MTJ that has the most compliance (i.e. has the least stiffness). Is this important functionally? I would bet it has some importance, but we simply don't know yet since no research, to my knowledge, has been done using this test which measures MTJ stiffness in multiple planes of motion.

Therefore, I believe that this difference in MTJ joint stiffness at multiple planes of externally applied manual force during the examination technique you describe may give us some valuable information, especially when some quality research is done, that may allow us to determine whether MTJ joint stiffness has anything to do with preferred motion patterns of the NC relative to the rearfoot. In my recent private discussions with podiatric researchers (I won't mention names, but you all know them), the concept of MTJ stiffness is a "hot topic" now and certainly your excellent description of the technique may eventually give impetus to researchers to see if, what I will call Dr. Root and Weed's MTJ Maximum Compliance Axis Test, has any correlation to the kinematic and kinetic function of the foot and lower extremity during weightbearing activities.
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Last edited by Kevin Kirby : 12th April 2009 at 10:03 PM.
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Old 12th April 2009, 08:38 PM
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Default Re: Midtarsal Joint Kinematics: Motion vs. Stiffness

Related threads:
Midfoot position, ROM and stiffness
The "Midtarsal Joint"...
GIB test of foot flexibility
Other threads tagged with mid-tarsal joint
Other threads tagged with stiffness
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Old 12th April 2009, 09:13 PM
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Default Re: Midtarsal Joint Kinematics: Motion vs. Stiffness

Quote:
Originally Posted by Kevin Kirby View Post
This new thread is split off from the thread Are Root Biomechanics Dying?


Jeff, Eric and Colleagues:

Instead, the examination technique you describe is a measure of MTJ stiffness, not of "the spatial location of the MTJ axis". In other words, when you perform this examination technique and find it more difficult to move the MTJ in one plane along one axis of motion rather than in another plane along another axis of motion, you are not determining "the spatial location of the MTJ axis" you are measuring the stiffness of the MTJ along each of it's many possible joint axes. You might claim that the MTJ has a vertical axis if the abduction-adduction direction of the navicular and cuboid (NC) relative to the rearfoot has the least joint stiffness. [Joint stiffness being defined as the amount of external force or external moment applied across the joint divided by the amount of joint rotation that occurs as a result of the applied external force or moment.] You might also claim that the MTJ definitely does not have a vertical axis if your applied manual force on the NC in the adduction-abduction direction produces less joint MTJ motion than when an adduction-plantarflexion and abduction-dorsiflexion external force is applied. Your examination technique rather than finding "the spatial location of the MTJ axis" is, I believe, determining the axis of motion of the MTJ that has the most compliance (i.e. has the least stiffness). Is this important functionally? I would bet it has some importance, but we simply don't know yet since no research, to my knowledge, has been done using this test which measures MTJ stiffness in multiple planes of motion.

Therefore, I believe that this difference in MTJ joint stiffness at multiple planes of externally applied manual force during the examination technique you describe may give us some valuable information, especially when some quality research is done, that may allow us to determine whether MTJ joint stiffness has anything to do with preferred motion patterns of the NC relative to the rearfoot. In my recent private discussions with podiatric researchers (I won't mention names, but you all know them), the concept of MTJ stiffness is a "hot topic" now and certainly your excellent description of the technique may eventually give impetus to researchers to see if, what I will call Dr. Root and Weed's Axis of Maximum MTJ Compliance Test, has any correlation to the kinematic and kinetic function of the foot and lower extremity during weightbearing activities.
Kevin, I think we have found some common ground here. Merton Root believed, except for the ankle joint, that you only need ounces of force to put the joints of the foot through their rom when the patient is relaxed. He attempted to replicate grf with ankle joint dorsiflexion, due to the tensile strength of the achilles tendon. By applying ounces of force, you find the path of least resistance of most joints, which is probably their most common path of motion. This doesn't mean, when the foot demands an additional rom or motion in a different plane, that potential motion isn't available. For example, an inversion ankle sprain isn't “normal" motion, but it is motion that occurs about an axis of rotation. In this case, the motion (axis) is contrary to the normal (average) motion at the joint and it results in trauma to the soft tissue. Bunions develop over time due to slight changes in force that result in microtrauma of the joint. They usually don't begin to hurt until this precoss becomes more advanced.

In terms of stiffness, you have passive restraints, such as ligaments and dynamic restraints, such as those produced by muscle contraction. I think our open chain examination is an evaluation of the passive constraints, since we conduct these test without muscle activity. During weight bearing activity, we rely on both passive and dynamic constraints. We know that motion and position can be altered very rapidly when either of these systems fails. Examples of this can be seen with tendon or ligamentous rupture or in upper motor issues, such as a CVA. The real challenge is in developing better systems to evaluate dynamic function.

Respectfully,
Jeff
www.root-lab.com
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Old 16th April 2009, 07:23 PM
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Default Re: Midtarsal Joint Kinematics: Motion vs. Stiffness

I've been pretty busy recently with development of my software and hardware, but I really appreciate special emphasis being placed on the midtarsal joints. Recently I had a relatively educational discussion on this topic with a manager of a new lab I am working with, in particular covering the movement of these joints.
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