Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Everything that you are ever going to want to know about running shoes: Running Shoes Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
  2. Have you considered the Critical Thinking and Skeptical Boot Camp, for taking it to the next level? See here for more.
    Dismiss Notice
  3. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

Subtalar Arthroereisis and Tibia Vara

Discussion in 'General Issues and Discussion Forum' started by adiraja108, Oct 30, 2011.

  1. adiraja108

    adiraja108 Member

    Members do not see these Ads. Sign Up.
    Hi all,

    I have a question in regards to subtalar arthroereisis and tibia vara.

    Many podiatrist advocate the use of a subtalar implant to reduce excess motion at the subtalar joint to about 5 degrees(?) pronation.

    If a patient with tibia vara undergoes the procedure, is it possible that the device can limit the calcaneal eversion necessary to compensate for a tibia vara, even if it allows the normal degress of "normal" pronation.

    Also, how will these devices effect a forefoot valgus deformity.. will it create more strain on the forefoot?

    Finally, on a little different issue...

    In feet with a rearfoot/tibia vara, the foot is inverted relative to the ground while in subtalar neutral, yes?

    If tibia vara is a big cause of pronation in feet and if a forefoot valgus often occurs alongside the tibia/rearfoot vara as the medial foot reaches toward the ground from an inverted position, then why would a medial forefoot post which allows the medial column to contact the ground sooner in the cycle, not be a good idea, ASSUMING that it does not adversely effect the windlass as Mr. Kirby has written about.

  2. efuller

    efuller MVP

    Yes. I've done EMED pressure plate analysis on patients after an arthroresis. I've seen very high lateral forefoot pressures.

    Maybe. I do a measurement that I call maximum eversion height. Patient standing, ask patient to evert, they will tend to use their peroneal muscles to evert their STJ and their MTJ. You look at the height of the lateral forefoot off of the ground. If someone cannot lift their lateral forefoot off of the ground an arthroesis would be a bad idea. I've seen people with 15 degrees of forefoot valgus that had a maximum eversion height of 2 mm. The forefoot to rearfoot matters much less than the eversion range of motion available.

    In the vast majority of feet, regardless of tibial position the heel bisection is inverted when the STJ is in neutral position. A bigger question is why do we care what the relation of the heel bisection to the ground is when the foot is in STJ neutral.

    Another question is why do we care about the motion of pronation. The motion of pronation doesn't hurt. It's the stopping of the motion that hurts.

    There are many interpretations of medial forefoot post. It appears you are describing a varus wedge under the forefoot. A varus forefoot wedge will tend to increase ground reaction force under the medial forefoot. This medial shift of force may not be far enough to create enough supination moment to change the position of the STJ. In feet with medially positioned STJ axes, force under the first met head is still on the pronation side of the STJ axis.

  3. drsarbes

    drsarbes Well-Known Member

    "If a patient with tibia vara undergoes the procedure, is it possible that the device can limit the calcaneal eversion necessary to compensate for a tibia vara, even if it allows the normal degress of "normal" pronation."

    Yes, absolutely.

    "Also, how will these devices effect a forefoot valgus deformity.. will it create more strain on the forefoot?"

    I have not performed a STJ Arthroereisis on a patient with a forefoot valgus. It would be unusual for a patient with a FF Valgus to provide the criteria for an arthroereisis procedure.

  4. adiraja108

    adiraja108 Member

    Hi Eric,

    So these lateral forefoot pressures would be due to lack of eversion range of motion or lateral deviation of the subtalar axis.. ie overcorrection?

    Regarding varus wedging, it took me a moment to understand but your saying that in a foot with a medial deviated subtalar axis the posting under the medial column would cause further pronation.. I was speaking more about it preventing the foot ( with a "normal" subtalar axis) from overpronating to find the ground whendue to the foot being inverted from a tibia/rearfoot varus.. meaning it would act as a "stopper" to keep the forefoot in the same plane as the inverted heel.

    Maybe it doesn't matter if the bisection of heel is inverted relative to the ground, but I was under the impression that the forefoot and the heel "like' to be on the same plane for optimum function.. hence the "comensated vs .uncompensated rearfoot varus." ?

    Thanks for the thoughts. :)
  5. adiraja108

    adiraja108 Member

    Hi Steve,

    So if a foot does not have the heel eversion necesary to compensate for a tibia/rear vara,(perhaps due to an overcorrected arthroereisis, then what would the result be in terms of pathology... I guess I am asking how does the pathology of an uncompensated rearfoot varus present clinically?
  6. efuller

    efuller MVP


    In gait, the foot hits the ground, and usually the STJ is slightly inverted from maximal pronation. When the lateral forefoot hits the STJ will pronate until something stops it. The something that stops it has to be a supination moment. The medial forefoot ( first met) will not create a supination moment if the the metatarsal is medial or even at the projection of the STJ axis. So, even with the forefoot varus wedge the STJ may still go to end of range of motion.

    Question what you were taught. Why would that be optimum?

  7. drsarbes

    drsarbes Well-Known Member

    "I guess I am asking how does the pathology of an uncompensated rearfoot varus present clinically?"
    Pain usually.

    You can get the engineering answer from the BioMech gurus here.

    As far as in a clinical setting, feet find a way.

    The problem with the STJ arthroereisis is the opposite. Many of these patients have quite a FF varus preoperatively; when you limit the STJ pronation they cannot easily get the first ray on the ground. At that point you can either get an orthotic to bring the ground up to the first ray or you can try and surgically bring the first ray down (not easy).

    If we could just get rid of gravity we wouldn't have all these concerns.

  8. adiraja108

    adiraja108 Member

    Okay, when the forefoot and the rearfoot are on the same plane, there is minimal tissue stress across the foot. If both planes are perpendicular to the ground, then there is a tripod effect and equalized pressure throughout the foot...

    If they are not in the same plane, the body weight will transmit unevenly through the foot during midstance and also create a moment about the stj axis unevenly... or in an effort to reach the ground evenly, the foot will be subject to torsional tissue stress.. which may result in a forefoot varus or valgus deformity...

    specifically the stj may have to overpronate at early midstance, which causes a supination issue at late midstance and possible heavy tissue stress at whatever mechanism is used to stop the pronation as you mentioned..

    So a rearfoot/tibia varus creates a situation where the foot and subtalar joint must compensate to feel the ground, which alters the timing of the gait cycle and creates soft tissue changes due the planar misalignment of the forefoot to rearfoot...

    and thats why this is bad.. :)
  9. adiraja108

    adiraja108 Member

    This is what I was asking actually... If the patient has trouble getting the medial column to the ground, why not bring the ground up under the first met... regardless of whether that creates a pron/sup moment.

    I assume if you use an orthotic to bring the ground up, the positing will be somewhere around the navicular?
  10. efuller

    efuller MVP

    Pain in the sinus tarsi or pain under lateral forefoot. If the medial column can't get to the ground (bear significant load) the location of the center of pressure of ground reaction force will be relatively far lateral. Specifically, lateral to the STJ axis and this will cause a relatively large pronation moment at the STJ. Then end of range of motion of the STJ is when the lateral process of the talus hits the floor of the sinus tarsi. If there is an arthroresis device then the end of range of motion is no longer the floor of the sinus tarsi, but the arthroresis device. The forces in this location have to create a supination moment equal and opposite the pronation moment from the ground. These forces can be quite high and hence the pain in this location.

  11. efuller

    efuller MVP

    If the first met is up in the air, and you have no further range of motion of the STJ to get the first met down, your only option is to bring the ground up to the first met. This should be done with a forefoot varus wedge/extension. If you go from no force on the first met to some force on the first met, you will shift the center of pressure medially, and this will reduce the pronation moment from the ground.

    In some of our earlier discussions we were talking about position and not moment. My point was that even if you change the moment from ground reaction force (with a forefoot varus wedge), you may not change the position.

    If you try to support the first ray at the navicular, you will lose your support after heel off in gait.

  12. efuller

    efuller MVP

    To lead you through the questioning of your assumptions...

    Define the rearfoot plane. Heel bisection is poor definition of a plane. The calcaneus does not have a flat bottom that must sit on the floor.
    The forefoot is more of a line than a plane. And a line isn't even that good of a descriptor. The metatarsal move indepnedently from each other.

    Why is rearfoot or tibial varus different than when that is not present. In gait, most feet will tend to hit heel, lateral forefoot and then medial forefoot. Most feet will try and "reach the ground". You may be making the erroneus assumption that the most feet start in neutral position.

  13. drsarbes

    drsarbes Well-Known Member

    In the cases I've done where we have substantially limited rear foot pronation in patents with a large FF varus, they ambulate with the first ray off the ground. Not very good to see in the office. The angle of gait is decreased and the push off is obviously abbreviated. These patients need an orthotic badly. In time some displace the implant and continue to pronate, which is why we try and evaluate preoperatively for this.

    This is not a foot that responds well to STJA procedures. I think when the MBA was first introduced, because it was a relatively simple procedure, it was over performed and criteria was lacking. Patients with semirigid RF deformities, fixed forefoot varus, talipes equinus - all were getting MBAs and nothing else. Not good. Not all surgeons who were performing implants felt comfortable performing achilles lengthenings, medial column fusions, etc...

    Again, I'm not a biomechanical expert; but I would suggest that a patient with an "uncompensated forefoot varus" is a rare bird. Like I said, the foot finds a way, especially on a planet with gravity and McDonald's.


Share This Page