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Midtarsal Joint Kinematics: Motion vs. Stiffness

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Apr 13, 2009.


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    This new thread is split off from the thread Are Root Biomechanics Dying?
    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.
     
    Last edited: Apr 13, 2009
  2. Admin2

    Admin2 Administrator Staff Member

  3. Jeff Root

    Jeff Root Well-Known Member

    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
     
  4. joejared

    joejared Active Member

    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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