Here is a video on the Subtalar Joint Axis Locator that Dr. Simon Spooner and I designed and developed together in 2005. We also had a radiographic study published on the use of the device in 2006 in JAPMA (Spooner SK, Kirby KA: The subtalar joint axis locator: A preliminary report. JAPMA, 96:212-219, 2006).
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Morphological adaptation of the tarso-metatarsal joints onto load transmission in the foot
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Heel walking more effiicent that forefoot walking
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Other threads on the subtalar joint axis -
Hi Kevin,
I am becoming increasingly aware of the need to accurately locate STJA. I have never seen your STJ Locator before and from this side of the screen in U.K. it looks somewhat fiddley. Just wondered what your opinion is on the accuracy of foot scanner STJA locator?
Regards
Issy -
What does "fiddley" mean? I don't know what a "foot scanner STJ axis locator" is. -
Isabel, in another post which seems to have vanished, you asked about clinical methods of determining the STJ axis location. Perhaps the most commonly employed technique is that described by Prof. Kirby in this paper: http://www.japmaonline.org/cgi/content/citation/77/5/228
I'm sure that if you ask nicely, Prof. Kirby will upload a copy for you. -
Bum bag = fanny pack
Weird unknown creatures = pigs
Foot scanner STJ axis locator = ? -
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I like it Kevin. Grid idea is easily understood and practical to implement.
I (presume to) know what you have implied with ankle sprains...in that a laterally deviated STJ will give supinators maximal mechanical advantage (and accordingly less protective output of peroneals) etc and facilitate inversion etc....
Any work or theories about the height of the STJ axis, and its connection between ankle instability?
Ron
Physiotherapist (Masters) & Podiatrist -
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Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987.
Kirby KA: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989.
Kirby KA, Green DR: Evaluation and Nonoperative Management of Pes Valgus, pp. 295-327, in DeValentine, S.(ed), Foot and Ankle Disorders in Children. Churchill-Livingstone, New York, 1992.
Kirby KA: Biomechanics of the normal and abnormal foot. JAPMA, 90:30-34, 2000.
Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001.
Van Gheluwe B, Kirby KA, Hagman F: Effects of simulated genu valgum and genu varum on ground reaction forces and subtalar joint function during gait. JAPMA, 95:531-541, 2005.Attached Files:
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Effects of Simulated Genu Valgum and Genu Varum on GRF and STJ Function During Gait.pdf
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Yes sorry, excuse my colloquial by 'fiddley' I mean awkward (Thank you simon.) I've no doubt you could show me how to use your STJA Locator but as I say from this side of the screen it looks abit 'fiddley';)
I think my terminology 'foot scanner STJ axis locator' was perhaps misleading. I was referring to the line which the foot scanners here plot on your scanned foot representing STJ angle. IT looks at the medial heel & lateral heel zone - when these zones are equal the angle is said to be equal to the foot axis. For each 10% deviation in either direction the angle goes 1 degree in that specific direction. I know that this is not actual STJ axis location as demonstrated by your video but I'm wondering if the two are closely linked. In otherwords would the angle plotted by the foot scanner be similar to the true STJ axis location?? I would appreciate your thoughts on this.
Regards
Issy -
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One way I can think of to use a pressure mapping system to estimate the STJ axis location would be to have someone stand on a pressure mat and pronate/ supinate their foot. Provided we could isolate STJ movement, as the subject pronates their foot the pressure beneath the area of the foot that is medial to the axis should increase while the area lateral to it should decrease and vice versa as the subject supinates their foot. If you could identify the zone between pressure increase and decrease, this should correspond to the transverse plane projection of the STJ axis. However, as we know, the STJ axis changes its location as the joint moves so in fact, what we would see in a pronating foot is that the zone between pressure increase and pressure decrease would sweep from lateral to medial across the foot as the foot/ axis changed position. The reverse should be true in supination. Assuming that we can't isolate STJ motion, what this technique would actually show is the transverse plane projection of the net rotational axis of the plantar foot. Interesting, if a little 1-dimensional.
I suspect this is something like what you trying to describe Issy. -
Are you talking about the RS Scan unit? -
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Yes I am referring to a RsScan system - wasn't sure if I was allowed to use product names on this site.
Regards
Issy -
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Issy -
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There is a bit of a story about this "STJ axis line" on the RS Scan system. To make a long story short, RS Scan is based out of Belgium, if I remember correctly. Friso Hagman (a Belgian biomechanist who I have coauthored a paper with Bart VanGheluwe) did his PhD thesis on "Can Plantar Pressure Predict Foot Motion" in which he was trying to determine the amount of frontal plane foot motion from pressure readings. From this work, I believe RS Scan now has a STJ line on their readout. I told the developer of the system, when he visited my office in Sacramento a few years ago, that the name should be changed since it probably didn't reflect STJ axis location and may confuse clinicians trying to use the system. Maybe it has been changed...but I don't know for sure.
As Simon stated, there are better ways to determine STJ axis location. Maybe, Issy, when you get out of this "fiddlley" stage you are in, you will learn the other ways that STJ axis spatial location may be more accurately assessed.:drinks -
http://www.japmaonline.org/cgi/content/abstract/96/4/305 -
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Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987.Attached Files:
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Thanks
Issy -
Issy -
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Issy -
Cheers,
Eric -
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Issy -
How do foot orthoses change the position of the net ground reaction force vector? -
Issy -
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Issy -
regards,
Eric -
So, the device made over the cast without the skive and a varus wedge under the rearfoot post will push upward more in the arch than a device with a medial heel skive. This may, or may not, be a good thing.
Regards,
Eric -
Also, changes in arch profile will impact on the stiffness of the arch section of the device. -
Issy -
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Don't think I'm answering this as you would like. Maybe you could suggest some reading related to orthosis and their effect on pressure distribution and net GRF.
<
Morphological adaptation of the tarso-metatarsal joints onto load transmission in the foot
|
Heel walking more effiicent that forefoot walking
>
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