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How to explore the subtalar joint axis?

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  #1  
Old 22nd December 2009, 07:32 AM
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Default How to explore the subtalar joint axis?

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Hi:

The assesment of articular range of motion of the STJA has got enormous clinical variability. What do you think is the "better" or more valid and reliable to do it?

1 - Exploration with the ankle in "neutral" position
2 - Exploration with the talocrural in a small dorsiflexion.
3 - Exploration in max. dorsiflexion of the talocrural

Likewise, which do you tkink that are the better contratomas (i.e where we put our distal hand)? do you think is valid to move de STJA from the fifth metatarsal head?

Bibliography is appreciated.

Greetings and sorry my english
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  #2  
Old 22nd December 2009, 08:30 AM
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Default Re: How to explore the STJA!?

Here some stuff for you. I´m sure there is lots more
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Old 22nd December 2009, 08:36 AM
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Default Re: How to explore the STJA!?

This maybe of interst as well.
Attached Files
File Type: pdf STJ_Axis_Locator._A_Preliminary_Report[1].pdf (1.50 MB, 51 views)
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Old 22nd December 2009, 10:56 AM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by JoseMiguel View Post
Hi:

The assesment of articular range of motion of the STJA has got enormous clinical variability. What do you think is the "better" or more valid and reliable to do it?

1 - Exploration with the ankle in "neutral" position
2 - Exploration with the talocrural in a small dorsiflexion.
3 - Exploration in max. dorsiflexion of the talocrural

Likewise, which do you tkink that are the better contratomas (i.e where we put our distal hand)? do you think is valid to move de STJA from the fifth metatarsal head?

Bibliography is appreciated.

Greetings and sorry my english
Jose:

In order to measure the quality of range of motion of the subtalar joint (STJ), here is the technique that I use.

Place the patient in a supine position, with their leg supported by the table or chair, and then grab their 4th and 5th metatarsal heads with one hand while using the other hand to stabilize the tibia from internally or externally rotating. Then, with the hand on the lateral metatarsal heads, load the forefoot into dorsiflexion with about 5-10 pounds of manual force which will stabilize the 4th and 5th metatarsal-cuboid joints, the calcaneo-cuboid joint and also cause an increase in tensile force within the Achilles tendon which is about double the compression loading force being used to manually load the 4th and 5th metatarsal heads. This loading of the lateral forefoot, when done correctly, will create a relatively stiff "beam" between between your hand (on the 4th and 5th metatarsal heads) and the subtalar joint which will allow you, in turn, to better determine the quality of range of motion of the STJ.

The hand on the lateral metatarsal heads is used to move the forefoot into adduction and abduction while placing a constant dorsiflexion loading force on the metatarsal heads, which will basically immobilize the talo-tibial joint so that STJ range of motion may be better appreciated. The following video







shows me performing the technique I have described above on a fresh-frozen cadaver foot at the Penn State Biomechanics Lab in September 2004. As you will notice, range of motion of the STJ by my placing the input force only on the 4th and 5th metatarsal head, causes very little movement of the talus (see bone pin that we drilled into the talus with the retro-reflective markers attached). This research eventually led to the following papers being published that showed that such a forefoot loading technique does relatively immobilize the ankle joint sufficiently to allow the movement of the calcaneus to the tibia to be a relatively accurate predictor of the three-dimensional location of the STJ axis:

Lewis GS, Kirby KA, Piazza SJ: Determination of subtalar joint axis location by restriction of talocrural joint motion. Gait and Posture. 25:63-69, 2007.

Lewis GS, Cohen TL, Seisler AR, Kirby KA, Sheehan FT, Piazza SJ: In vivo tests of an improved method for functional location of the subtalar joint axis. J Biomechanics, 42:146-151, 2009.

Hope this helps.

Feliz Navidad!!
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  #5  
Old 22nd December 2009, 03:11 PM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by JoseMiguel View Post
Hi:

The assesment of articular range of motion of the STJA has got enormous clinical variability. What do you think is the "better" or more valid and reliable to do it?

1 - Exploration with the ankle in "neutral" position
2 - Exploration with the talocrural in a small dorsiflexion.
3 - Exploration in max. dorsiflexion of the talocrural

Likewise, which do you tkink that are the better contratomas (i.e where we put our distal hand)? do you think is valid to move de STJA from the fifth metatarsal head?

Bibliography is appreciated.

Greetings and sorry my english
To add to Kevin's excellent post:
It doesn't really matter what position the ankle is in as long as the ankle doesn't move when you are assessing the axis. I find it easiest to keep the ankle from moving, as kevin described, when the ankle is dorsiflexed so that there is some resistance in the Achilles tendon. To verify that the ankle is not moving you can palpate the talar dome at the anterior aspect of the ankle with and without ankle movement to verify for yourself whether or not the ankle is moving.

You don't want to confuse motion of other joints with motion of the subtalar joint.

Regards,

Eric
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  #6  
Old 25th December 2009, 09:38 AM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by m weber View Post
This maybe of interst as well.
Thanks a lot Michael. But, i`m questioning about how valid is these different ways to explore STJA motion.

Regards
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Old 25th December 2009, 09:57 AM
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Default Re: How to explore the STJA!?

Hi Kevin and all!

Quote:
Originally Posted by Kevin Kirby View Post
Jose:
which will basically immobilize the talo-tibial joint so that STJ range of motion may be better appreciated. The following video ........., causes very little movement of the talus (see bone pin that we drilled into the talus with the retro-reflective markers attached).
This is i´m questioning (sorry my ignorance!). Really, the talus is not perfectly inmobilized. In fact, in the video, it´s possible to apreciate a little movement in the talus. This is, in this way i think we´re not assesing only the STJA. I remember that in your article, the talo-tibial movement was a good predictor of the calcaneus-talo movement, but not were the same.

Because, i think probably would be more valid to assess this with maxima dorsiflexion of the talocrural, in this way, the talus is more inmobilized between fibula and tibia. This could explain why people who have limited dorsiflexion of the talocrural, exhibit sometimes a "more pronated STJ" during gait, especially in the midstance.


It´s only my humble opinion!!
Thanks a lot


Quote:
Originally Posted by Kevin Kirby View Post

Feliz Navidad!!
The same to you
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  #8  
Old 25th December 2009, 10:14 AM
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Default Re: How to explore the STJA!?

Hi Eric and all!!

Quote:
Originally Posted by efuller View Post
To add to Kevin's excellent post:
It doesn't really matter what position the ankle is in as long as the ankle doesn't move when you are assessing the axis.
Eric
But it´s not easy to know if the talus is moving or not, depending on the patient. Palpating is not fiable, although it´s a good idea.

When i explore STJA movement, the quality and quantity of movement is very different if the talocrural is neutral or maximaly dorsioflexioned. For example, the pronation range of motion is minor with max dorsiflexion, in part this is because tension in Aquilles tendon, but perhaps in part is because the talus is "more blocked" (talus wider in the anterior body).

And in fact, during gait, the STJ pronates especially in the midstance phase of gait, where there is a max dorsiflexion of the talocrural. In this way, at least we can evaluate this "time of the STJ movement", where a lot of patology is suggested to occur....)

Thanks a lot to resolve my doubts!!

Regards
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  #9  
Old 25th December 2009, 10:51 AM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by JoseMiguel View Post
This is i´m questioning (sorry my ignorance!). Really, the talus is not perfectly inmobilized. In fact, in the video, it´s possible to apreciate a little movement in the talus. This is, in this way i think we´re not assesing only the STJA. I remember that in your article, the talo-tibial movement was a good predictor of the calcaneus-talo movement, but not were the same.

Because, i think probably would be more valid to assess this with maxima dorsiflexion of the talocrural, in this way, the talus is more inmobilized between fibula and tibia. This could explain why people who have limited dorsiflexion of the talocrural, exhibit sometimes a "more pronated STJ" during gait, especially in the midstance.
When Greg Lewis, Steve Piazza and I were performing the cadaver research at Penn State five years ago, we had discussed how much forefoot loading force would be best to truly immobilise the talus against the tibia without causing other problems in assessing STJ motion by moving the foot relative to the tibia. One of the reasons we didn't use greater forefoot loads while assessing STJ range of motion is that we were worried that if we used forefoot loads that were too great then we would get much more elongation (i.e. creep) during forefoot loading within the plantar fascia, plantar ligaments and Achilles tendon. In other words, we wanted to use the smallest forefoot load that would not only relatively immobilize the talus on the tibia without causing other issues such as the Achilles tendon, plantar fascia and plantar ligaments all stretching during the assessment procedure and thus causing more error in our results.

Hope this makes sense.
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Kevin

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California School of Podiatric Medicine at Samuel Merritt College

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  #10  
Old 25th December 2009, 03:36 PM
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Default Re: How to explore the STJA!?

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Old 29th December 2009, 10:17 AM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by Kevin Kirby View Post
When Greg Lewis, Steve Piazza and I were performing the cadaver research at Penn State five years ago, we had discussed how much forefoot loading force would be best to truly immobilise the talus against the tibia without causing other problems in assessing STJ motion by moving the foot relative to the tibia. One of the reasons we didn't use greater forefoot loads while assessing STJ range of motion is that we were worried that if we used forefoot loads that were too great then we would get much more elongation (i.e. creep) during forefoot loading within the plantar fascia, plantar ligaments and Achilles tendon. In other words, we wanted to use the smallest forefoot load that would not only relatively immobilize the talus on the tibia without causing other issues such as the Achilles tendon, plantar fascia and plantar ligaments all stretching during the assessment procedure and thus causing more error in our results.

Hope this makes sense.
Thanks a lot Kevin. Sorry i´m too late.

Sometimes, when i asses the STJ in the way yo do, i usually "grab" the talus pressing in tibia and fibula trying to inmobilise the talus, do you think is a good idea??

Thank you for your comments in this wonderful forum.

Regards and happy 2010!!
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Old 29th December 2009, 10:18 AM
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Default Re: How to explore the STJA!?

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Related threads:
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Thanks admin, i´ll not be boring this new year.....
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Old 29th December 2009, 04:04 PM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by JoseMiguel View Post
Thanks a lot Kevin. Sorry i´m too late.

Sometimes, when i asses the STJ in the way yo do, i usually "grab" the talus pressing in tibia and fibula trying to inmobilise the talus, do you think is a good idea??

Thank you for your comments in this wonderful forum.

Regards and happy 2010!!
I'm having a hard time imagining grabbing a foot or leg in such a way that you would imobilize the talus in the ankle joint. The talus is prettty slippery. In my interpretation of English, "grabbing" would mean trying to squeeze the tibia and fibula together. Is that what you mean? You can sort of immobilize the talus by pushing it toward its end of range of motion in either plantar flexion or dorsiflexion and keep pushing to hold it there.

Happy new year,

Eric
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Old 30th December 2009, 02:47 AM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by efuller View Post
I'm having a hard time imagining grabbing a foot or leg in such a way that you would imobilize the talus in the ankle joint. The talus is prettty slippery. In my interpretation of English, "grabbing" would mean trying to squeeze the tibia and fibula together. Is that what you mean? You can sort of immobilize the talus by pushing it toward its end of range of motion in either plantar flexion or dorsiflexion and keep pushing to hold it there.

Happy new year,

Eric
Hi Eric!

I understand you, thanks a lot for your answer.

Happy 2010!
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Old 29th September 2011, 04:28 AM
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Default Re: How to explore the STJA!?

My only problem with this entire discussion on measuring STJ ROM, is that all of the techniques described here place the ankle in in a neutral or slight dorsiflexed position.
Our society wears shoes that place our ankle into slight PF at all times.. at least 14-20 mm of height.
doesn't your evidence of measuring STJ and description of STJ motion with foot in a neutral anatomic position support going barefoot??? If not, there is no basis for even determining STJ axis or motion because we negate our findings by placing the foot in a shoe....
Nick Campitelli, DPM, FACFAS


Quote:
Originally Posted by Kevin Kirby View Post
Jose:

In order to measure the quality of range of motion of the subtalar joint (STJ), here is the technique that I use.

Place the patient in a supine position, with their leg supported by the table or chair, and then grab their 4th and 5th metatarsal heads with one hand while using the other hand to stabilize the tibia from internally or externally rotating. Then, with the hand on the lateral metatarsal heads, load the forefoot into dorsiflexion with about 5-10 pounds of manual force which will stabilize the 4th and 5th metatarsal-cuboid joints, the calcaneo-cuboid joint and also cause an increase in tensile force within the Achilles tendon which is about double the compression loading force being used to manually load the 4th and 5th metatarsal heads. This loading of the lateral forefoot, when done correctly, will create a relatively stiff "beam" between between your hand (on the 4th and 5th metatarsal heads) and the subtalar joint which will allow you, in turn, to better determine the quality of range of motion of the STJ.

The hand on the lateral metatarsal heads is used to move the forefoot into adduction and abduction while placing a constant dorsiflexion loading force on the metatarsal heads, which will basically immobilize the talo-tibial joint so that STJ range of motion may be better appreciated. The following video







shows me performing the technique I have described above on a fresh-frozen cadaver foot at the Penn State Biomechanics Lab in September 2004. As you will notice, range of motion of the STJ by my placing the input force only on the 4th and 5th metatarsal head, causes very little movement of the talus (see bone pin that we drilled into the talus with the retro-reflective markers attached). This research eventually led to the following papers being published that showed that such a forefoot loading technique does relatively immobilize the ankle joint sufficiently to allow the movement of the calcaneus to the tibia to be a relatively accurate predictor of the three-dimensional location of the STJ axis:

Lewis GS, Kirby KA, Piazza SJ: Determination of subtalar joint axis location by restriction of talocrural joint motion. Gait and Posture. 25:63-69, 2007.

Lewis GS, Cohen TL, Seisler AR, Kirby KA, Sheehan FT, Piazza SJ: In vivo tests of an improved method for functional location of the subtalar joint axis. J Biomechanics, 42:146-151, 2009.

Hope this helps.

Feliz Navidad!!
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Old 29th September 2011, 06:39 AM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by nickcampi View Post
My only problem with this entire discussion on measuring STJ ROM, is that all of the techniques described here place the ankle in in a neutral or slight dorsiflexed position.
Our society wears shoes that place our ankle into slight PF at all times.. at least 14-20 mm of height.
doesn't your evidence of measuring STJ and description of STJ motion with foot in a neutral anatomic position support going barefoot??? If not, there is no basis for even determining STJ axis or motion because we negate our findings by placing the foot in a shoe....
Nick Campitelli, DPM, FACFAS
How does placing the foot in a shoe change the position of the STJ axis?

I don't think that it does. There are two different things here. The position of the axis and the position of the joint within it's range of motion. Most of this discussion is about the position of the joint axis. The position of the axis is important in determining the moment from ground reaction force about the joint. The position of the axis is determined by the shape of the articular facets of the talus and calcaneus. A few degrees of ankle joint motion will not significantly change the projection of the STJ axis onto the transverse plane.

Eric
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Old 29th September 2011, 07:57 AM
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Default Re: How to explore the STJA!?

Quote:
Originally Posted by nickcampi View Post
My only problem with this entire discussion on measuring STJ ROM, is that all of the techniques described here place the ankle in in a neutral or slight dorsiflexed position.
Our society wears shoes that place our ankle into slight PF at all times.. at least 14-20 mm of height.
doesn't your evidence of measuring STJ and description of STJ motion with foot in a neutral anatomic position support going barefoot??? If not, there is no basis for even determining STJ axis or motion because we negate our findings by placing the foot in a shoe....
Nick Campitelli, DPM, FACFAS
Hi Nick:

I see you are on the "Medical Advisory Board for Vibram FiveFingers".

http://akronpodiatrist.blogspot.com/...-advisory.html

How can you recommend a shoe such as the Vibram FiveFingers that causes so many metatarsal stress fractures in runners?

http://www.podiatry-arena.com/podiat...ad.php?t=48566
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Kevin

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Website: www.KirbyPodiatry.com

Private Practice:
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**************************************************
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Old 29th September 2011, 08:15 AM
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Default Re: How to explore the subtalar joint axis?

Quote:
Originally Posted by nickcampi View Post
My only problem with this entire discussion on measuring STJ ROM, is that all of the techniques described here place the ankle in in a neutral or slight dorsiflexed position.
Our society wears shoes that place our ankle into slight PF at all times.. at least 14-20 mm of height.
doesn't your evidence of measuring STJ and description of STJ motion with foot in a neutral anatomic position support going barefoot??? If not, there is no basis for even determining STJ axis or motion because we negate our findings by placing the foot in a shoe....
Nick Campitelli, DPM, FACFAS
Figure 8. Next.....
Attached Files
File Type: pdf STJ Axis Locator. A Preliminary Report.pdf (1.50 MB, 8 views)
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Old 29th September 2011, 09:41 AM
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Default Re: How to explore the STJA!?

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Originally Posted by efuller View Post
How does placing the foot in a shoe change the position of the STJ axis?

I don't think that it does. There are two different things here. The position of the axis and the position of the joint within it's range of motion.
Eric, the best research we have shows that the STJ axial position changes in relation to the joints position. The question is, do we have research showing that shoes change the STJ dynamic phase and range of motion? If so, we must also conclude that shoes alter STJ axial position. My feeling is that shoes do alter dynamic STJ axial position.

Here's the caveat: Mr Vibram medical committee, Nick, whatever your name is, this does not necessarily mean that walking or running barefoot is best. To quote the now defunked REM- "you can't get there from here". Please take note: http://www.youtube.com/watch?v=gD3cYh5Pp1I


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Quote:
Originally Posted by nickcampi View Post
doesn't your evidence of measuring STJ and description of STJ motion with foot in a neutral anatomic position support going barefoot???
NO, IT DOES NOT! Like the man said: you can't get there from here. End of story. Remind me what it was that you were trying to sell? Even better; try to argue your position here.
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Old 29th September 2011, 12:39 PM
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Default Re: How to explore the subtalar joint axis?

Quote:
My only problem with this entire discussion on measuring STJ ROM, is that all of the techniques described here place the ankle in in a neutral or slight dorsiflexed position.
Our society wears shoes that place our ankle into slight PF at all times.. at least 14-20 mm of height.
doesn't your evidence of measuring STJ and description of STJ motion with foot in a neutral anatomic position support going barefoot??? If not, there is no basis for even determining STJ axis or motion because we negate our findings by placing the foot in a shoe....
Nick Campitelli, DPM, FACFAS
Nick:

The experiment we were doing at the Penn State Biomechanics Lab had nothing to do with your ill-conceived notion that barefoot is better and using "minimalist" shoes is better. I honestly find it hard to believe that any podiatrist could jump to that conclusion unless they had no concept at all of foot and lower extremity biomechanics and the nature of scientific research investigation or possibly they had a financial interest in "minimalist shoes".

During the experiment demonstrated on video with Steve Piazza, PhD, (now one of the editors for the Journal of Biomechanics) and Greg Lewis, PhD (who was working on his PhD at the time) from the Penn State Biomechanics Department, we were looking to see if my manual method of pushing on the bottom of the foot correlated to the actual spatial location of the subtalar joint (STJ) axis found through 3D kinematics with a 3D motion analysis system. This experiment led to the development of a unique 3D motion analysis method of finding the STJ axis spatial location without drilling a pin into the talus of live subjects. Our research had nothing to do with whether being shod or barefoot is better or worse for individuals in the modern society that most of us live in.

Here are the reference papers that deal with that research at Penn State and subsequent research that developed from that research.

Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987.

Lewis GS, Kirby KA, Piazza SJ: A motion-based method for location of the subtalar joint axis assessed in cadaver specimens. Presented at 10th Anniversary Meeting of Gait and Clinical Movement Analysis Society in Portland, Oregon. April 7, 2005.

Lewis GS, Kirby KA, Piazza SJ: Determination of subtalar joint axis location by restriction of talocrural joint motion. Gait and Posture. 25:63-69, 2007.

Lewis GS, Cohen TL, Seisler AR, Kirby KA, Sheehan FT, Piazza SJ: In vivo tests of an improved method for functional location of the subtalar joint axis. J Biomechanics, 42:146-151, 2009.
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Old 29th September 2011, 09:13 PM
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Default Re: How to explore the STJA!?

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Originally Posted by Simon Spooner View Post
Eric, the best research we have shows that the STJ axial position changes in relation to the joints position. The question is, do we have research showing that shoes change the STJ dynamic phase and range of motion? If so, we must also conclude that shoes alter STJ axial position. My feeling is that shoes do alter dynamic STJ axial position.
Simon, I agree. If there was data that showed that shoes changed STJ position then I would agree that that the shoes could change the location of the axis. However, if you got a 2 degree change in position of the STJ, would you get a significant change in the location of the STJ axis. Suppose you assumed that you got a 1:1 transverse to frontal plane ratio of motion. Two degrees of inversion of the calcaneus would get you 2 degrees of external talar rotation and since the axis is determined by the joint facets you could assume that you get a 2 degree change of the projection of the axis on to the transverse plane. Yes, changing the position of the axis is theoretically possible, but is it significant in practice?

Eric
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Old 30th September 2011, 06:03 AM
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Default Re: How to explore the STJA!?

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Originally Posted by efuller View Post
Simon, I agree. If there was data that showed that shoes changed STJ position then I would agree that that the shoes could change the location of the axis. However, if you got a 2 degree change in position of the STJ, would you get a significant change in the location of the STJ axis. Suppose you assumed that you got a 1:1 transverse to frontal plane ratio of motion. Two degrees of inversion of the calcaneus would get you 2 degrees of external talar rotation and since the axis is determined by the joint facets you could assume that you get a 2 degree change of the projection of the axis on to the transverse plane. Yes, changing the position of the axis is theoretically possible, but is it significant in practice?

Eric
Eric, lets take your two degree change in the transverse plane projection, what if that 2 degree change increases or decreases the distance from the net GRF vector to the joint axis by 100%?
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Old 30th September 2011, 08:04 AM
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Default Re: How to explore the STJA!?

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Originally Posted by Simon Spooner View Post
Eric, lets take your two degree change in the transverse plane projection, what if that 2 degree change increases or decreases the distance from the net GRF vector to the joint axis by 100%?
Ok I'll play. So, to move the axis in the transverse plane you have to leg/ talus rotation. The axis of rotation in the transverse plane is (guessing) under the posterior part of the talus. So, a 2 degree rotation of the talus will create essentially no change in the axis at the posterior foot. At the met heads, assuming a 20cm distance from the pivot point to the met heads, the distance moved would be sine2 x 20 cm. 0.034899497 x20 = approximately 7mm. 10mm distance from the pivot point = 3.5 mm. in stance the Cop may only be 5cm from pivot point for a change of 1.8mm

So, to change the distance from the axis 100% the original distance would have to be 7mm or quite small. The moment from the ground would be small in relation to the moments from the muscles.

It is much easier to get a few degrees of eversion of the STJ in the foot that has eversion range of motion than it is to get inversion of the STJ. So, the axis position change is quite relevant in the "oversupinator". However, when we are trying to increase supination moment, the changing of the location of the force will have to move quite far to overcome the "residual pronation moment" to get the added effect of moving the axis as well. (The added effect is the lateral shift of the axis that comes with supination of the STJ). Often you don't see a change in STJ position with varus wedge effect. (How often might be a relatively easy research project for someone.)

Eric

Last edited by efuller : 30th September 2011 at 08:05 AM. Reason: forgot to delete something
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Old 30th September 2011, 08:54 AM
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Default Re: How to explore the STJA!?

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Originally Posted by efuller View Post
Ok I'll play. So, to move the axis in the transverse plane you have to leg/ talus rotation. The axis of rotation in the transverse plane is (guessing) under the posterior part of the talus. So, a 2 degree rotation of the talus will create essentially no change in the axis at the posterior foot. At the met heads, assuming a 20cm distance from the pivot point to the met heads, the distance moved would be sine2 x 20 cm. 0.034899497 x20 = approximately 7mm. 10mm distance from the pivot point = 3.5 mm. in stance the Cop may only be 5cm from pivot point for a change of 1.8mm

So, to change the distance from the axis 100% the original distance would have to be 7mm or quite small. The moment from the ground would be small in relation to the moments from the muscles.

It is much easier to get a few degrees of eversion of the STJ in the foot that has eversion range of motion than it is to get inversion of the STJ. So, the axis position change is quite relevant in the "oversupinator". However, when we are trying to increase supination moment, the changing of the location of the force will have to move quite far to overcome the "residual pronation moment" to get the added effect of moving the axis as well. (The added effect is the lateral shift of the axis that comes with supination of the STJ). Often you don't see a change in STJ position with varus wedge effect. (How often might be a relatively easy research project for someone.)

Eric
Eric, I'm not going to argue with your calculations, but if the net ground reaction force vector is 1mm from the axis when barefoot, but 2mm from the axis when shod, that's the moment doubled, all other factors being equal. Move it by a further mm and the net moment is now tripled. While in actual terms the distance change might be small, in percentage terms the effect on the net moment might be quite large.

A transverse plane projection is an obvious start, but when my Mrs straps on her four inch heels for work each day in suspect there is greater change of the STJ axis in relation to the net GRF vector in the other planes. I recall drawing this out for a thread here some years ago as a frontal plane section. Take a non-vertical GRF vector and a frontal plane section, elevate the STJ axial position from the supporting surface in 1mm increments. Soon adds up. This is what I was trying to work out when Kevin sent me his sketch for the STJ axis locator. What happens to the relationship between the STJ axis and the net GRF vector after heel lift?
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Old 30th September 2011, 09:27 AM
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Default Re: How to explore the subtalar joint axis?

Eric and Simon won´t adding a shoe also have effect on the lateral side of the STJ axis as well.

as in will is not negate some what the change in the STJ axis position from adding shoe wear
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Old 30th September 2011, 01:48 PM
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Default Re: How to explore the subtalar joint axis?

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Originally Posted by mike weber View Post
Eric and Simon won´t adding a shoe also have effect on the lateral side of the STJ axis as well.

as in will is not negate some what the change in the STJ axis position from adding shoe wear
Moment is determined by location of center of pressure and location of the axis.

A lateral flare on the heel of the shoe will change the location of force relative to the axis. It may not change the position of the joint within its range of motion.

Simon and I were discussing the location of the joint axis, which does change with a change in STJ position. The question is whether a shoe can create a large enough change in joint position to change the location of the axis. After thinking about it, I'd agree that in those feet with pronation range of motion available many treatment options can easily pronate the STJ further to change the location of the axis. However finding treatment modalities that can significantly supinate the STJ so that the axis moves is going to be hard. Especially in feet that you want to supinate. Yes, you can change the location of center of pressure, but in a food with a highly medially deviated STJ axis it's going to be hard to find a treatment modality, that will be comfortable to wear, that will hold the foot in a more supinated position so that the location of the axis has moved.

Eric
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Old 30th September 2011, 07:36 PM
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Default Re: How to explore the subtalar joint axis?

I just love the above calculations and the equation!

Ok I'll play. So, to move the axis in the transverse plane you have to leg/ talus rotation. The axis of rotation in the transverse plane is (guessing) under the posterior part of the talus. So, a 2 degree rotation of the talus will create essentially no change in the axis at the posterior foot. At the met heads, assuming a 20cm distance from the pivot point to the met heads, the distance moved would be sine2 x 20 cm. 0.034899497 x20 = approximately 7mm. 10mm distance from the pivot point = 3.5 mm. in stance the Cop may only be 5cm from pivot point for a change of 1.8mm

"Assume 20cm................... and then to have nine decimal places? Spurious accuracy, one thinks to one's self.
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Old 1st October 2011, 03:27 PM
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Default Re: How to explore the subtalar joint axis?

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Originally Posted by Rob Kidd View Post
I just love the above calculations and the equation!

Ok I'll play. So, to move the axis in the transverse plane you have to leg/ talus rotation. The axis of rotation in the transverse plane is (guessing) under the posterior part of the talus. So, a 2 degree rotation of the talus will create essentially no change in the axis at the posterior foot. At the met heads, assuming a 20cm distance from the pivot point to the met heads, the distance moved would be sine2 x 20 cm. 0.034899497 x20 = approximately 7mm. 10mm distance from the pivot point = 3.5 mm. in stance the Cop may only be 5cm from pivot point for a change of 1.8mm

"Assume 20cm................... and then to have nine decimal places? Spurious accuracy, one thinks to one's self.
Actually, it was out of laziness, that was the result from excell. The final result was rounded so I wasn't implying that level of accuracy. It's perfectly valid to plug some numbers in to get a rough estimate of the magnitude of change in moment.



Eric
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