Midtarsal Joint Equilibrium Theory

which is why power flow is important and why does the leg drives the stj ? in our leg stiffness discussions was important for you to discuss.

I´m off to read all the papers again and look at the picture through new eyes.

all learning - all good to me :drinks

 

OK
So, let the red circle be the centre of pressure position (COP), let the vector be vertical, let the green line be the subtalar joint (STJ )axis. Does this arrangement result in in-phase or out-of-phase motion between the STJ and midtarsal joints (MTJ) given the MTJ axial position B?

Lets pin the tail on the donkey, can you position the COP such that the resultant motion of the STJ and MTJ should be in-phase with MTJ axis B?

 

So, given this single plane analysis, placing the COP anywhere within the yellow or blue boxes gives us in-phase motion between the STJ and MTJ given MTJ axis B- right? Anywhere outside of these boxes gives us out of phase motion- right? (in theory you could extend the boxes outside of the foot diagram to infinity, perpendicular to where each box meets the axes on two sides, but lets not take the piss, smart arses)

Now try the same for MTJ axial positions A and C...

 

My head hurts....

Not sure if it's this thread or the baby teething :wacko:

Excellent discussion though...as usual Spooner.

 

Nice to have you back on the show, Dave.

All of us Happy fathers- Deco PM'd me a couple of days ago about potty training.... I've now got a 5 1/2 year old who thinks she's 15

 

Let me attempt to better clarify the specific mechanics of the midtarsal joint from my viewpoint:

The point of application, direction, magnitude and line of action of the external force(s) acting on the foot, in combination with the internal forces acting across the structural components of the midtarsal joint, will determine the kinematics and instantaneous axis of motion of the midtarsal jont. If there is a change in the external forces, such as a shift to another point of application of force or a change to a different spatial location of the force vector, then it is very likely that the instantaneous axis of the midtarsal joint will also change in spatial location. Therefore, in the specific case of the midtarsal joint, which is one of most unconstrained joints in the human foot, the external forces and internal forces acting across the midtarsal joint are predominantly reponsible for the midtarsal joint axis of motion. As a result, to assume any predetermined axis of motion of the midtarsal joint without first considering the external and internal forces that first caused that specific axis of motion of the midtarsal joint to occur, is likely to be an exercise in futility, and will likely be fraught with clinical assumptions that, in reality, do not exist within this unique joint of the human foot.

 

I would like to make a summary see I´ve got this sorted.

1 Midtarsal joint motion as defined by Nester et al

Inversion,Eversion around the x-axis,
Dorsiflexion, Plantarflexion around the z-axis
Adduction, Abduction around the y-axis.

2 Motion at these 3 axis may occur in any order according to where the forces and the axis lie - Ie using pronation and supination at the midtarsal joint may not work as we may have new combinations of triplane motion.

example -

3 The MTJ axis is much more Fluid or as Simon put it - The MTJ is "less constrained" than the STJ so there will be a larger envelope for the axial positions.

4 or as Kevin put it- And it is because of the relative non-constraint of the midtarsal joint (MTJ), especially when compared to the relatively highly constrained subtalar joint (STJ) that it will be impractical, if not highly unlikely, that we will be able to determine the kinetics of the MTJ by assigning it a single spatial axis location, unless that axis has first been determined by a time-consuming 3D kinematic analysis

5 So the MTJ axis will only be in that position for microseconds as change position a great deal.

6 the MTJ axis spartial location is controlled by Motion or as Simon put it - Forces and axial position determine the moments, moments determine the motion, motion determines the axial position,

or as Kevin wrote - The point of application, direction, magnitude and line of action of the external force(s) acting on the foot, in combination with the internal forces acting across the structural components of the midtarsal joint, will determine the kinematics and instantaneous axis of motion of the midtarsal jont. If there is a change in the external forces, such as a shift to another point of application of force or a change to a different spatial location of the force vector, then it is very likely that the instantaneous axis of the midtarsal joint will also change in spatial location. Therefore, in the specific case of the midtarsal joint, which is one of most unconstrained joints in the human foot, the external forces and internal forces acting across the midtarsal joint are predominantly reponsible for the midtarsal joint axis of motion. As a result, to assume any predetermined axis of motion of the midtarsal joint without first considering the external and internal forces that first caused that specific axis of motion of the midtarsal joint to occur, is likely to be an exercise in futility, and will likely be fraught with clinical assumptions that, in reality, do not exist within this unique joint of the human foot.


7 Joint coupling and in and anti phase motion maybe important to consider when looking at Kinematics of joints in this case the MTJ-

Hope thats a good summary-

Question time - Will this mean that to clincially determine the Kinematics and spartial location of the MTJ axis Force and Pressure scanning will be needed ?

If thinking tissue stress and the MTJ the knowledge of not just what tissue is under stress, but when it´s understress will be vitial to work out the why it´s under stress .

 

In and anti phase . The PDF defined anti phase as

So in phase would be rearfoot inversion - forefoot inversion ????

if I´m thinking correctly won´t the yellow area be with other motion be eversion at the MTJ and the blue be inversion at the STJ with other motions. so these would be motions rotating in opposite directions - anti-phase not in-phase.

Sorry hitting another speed hump I think. :sinking:

 

COP within the yellow box would create eversion moment about both the MTJ axis B and the STJ axis. COP within the blue box would create inversion moment about both the STJ axis and MTJ axis B. So if the COP were within the blue box= both segments inverting, if COP were within yellow box= both segments everting.

 

God I´m a tool - COP can´t be in 2 places at once.

IDIOT !!!:bang:

This should be for MTJ axis A if COP is in the blue or yellow area in-phase motion should occur at the MTJ and STJ axis. The area is smaller and this maybe important on orthotic prescription ie where ORF (orthtoic reaction force) is placed.

EDIT : I´m slightly 2nd guessing the yellow area , due to the different angle of the MTJ axis, but COP in the yellow area will cause an external dorsiflexion moment at the MTJ and STJ and in may not cause much of a eversion moment at the MTJ but will at the STJ . I think.

 

Simon

Are the yellow and blue boxes arbitrary or have you defined them based on something?

Sorry to be thick but this concept of in/out of phase is taking a bit off sinking in.

Phil

 

Phil, given the MTJ axis labelled "B" and the green line representing the STJ axis, these boxes represent areas of the foot in which the centre of pressure would result in the same direction moment acting about both the STJ axis and the MTJ axis "B"

 

I'm not sure it's so simple for axes A and C because their orientation is so different from the STJ axis. I'll try and work it through later. Remember too that I'm just trying to help with understanding in-phase and out of phase here and I am using the axis reported by Nester to help with this. When you put an orthotic under a foot, your going to influence the axial position if you alter the movement pattern.

Why not try this Mike: Again with a transverse plane image of the foot, draw in an x axis for the MTJ, through the midfoot at the level of the talar head (this will give you your sagittal plane moments (dorsiflexion and plantarflexion), draw in you STJ axis and plot your in-phase areas. Then repeat for a Y axis for the MTJ longitudinal through foot (not sure where you'd position this, maybe between the TNJ and CCJ), this will give you your frontal plane moments (inversion and eversion) and repeat as above. Have fun.

 

Michael:

I think this is an excellent summary. However, I'm not so sure about Simon's game with in-phase and out of phase motion. It doesn't make much sense to me either. Maybe he just likes to make colored boxes on feet.

 

The great thing is Kevin, "you don't have to buy it". :drinks I think Michael does understand the point I'm trying to make though.

 

Ok,

Heres pictures
1 x axis Yellow = COP = Dorsiflexion in phase at STJ and at MTJ
Blue = COP = Plantarflexion in phase at STJ and at MTJ

 

Next Y axis Yellow = COP = Eversion in- phase at MTJ and STJ

Blue = COP = Inversion in-phase at MTJ and STJ.

 

Nice work Michael. So the position of the STJ axis projected onto the transverse plane will have an influence in the size and location of the area of the foot in which the external moment from ground reaction forces (located at the centre of pressure) might result in out of phase moments about the subtalar and midtarsal joint axes. Specifically, with regard to the MTJ "Y" axis, the more medially deviated the STJ axis the greater the out of phase area- right? So lets take your "y axis" diagram above and place our COP on the second met head, if this was the only force acting on the foot what motion would you see at the STJ and MTJ respectively in regard to inversion / eversion? Now overlay the X axis diagram and you'll see that the STJ and MTJ should be in-phase with the COP here, so we would have dorsiflexion about both the STJ and MTJ axes from our COP at the 2nd metatarsal head, but with inversion at the MTJ and eversion at the STJ- would would this do to the foot's position?

This analysis is limited though because we have so far only looked at external moment via the COP. Why not repeat the process you did above only this time add in some muscular insertions..... see which muscles would generate internal moments that are in phase about the axes and which ones would generate moments that are out of phase.

Your going great, Mike.

This makes sense to me, but if it doesn't to anyone else please speak up.

 

If you accept that:

1) the MTJ is a relatively non-constrained joint of the foot,

2) the location of the CoP will have a large effect in determining the spatial location of the axis of motion of the midtarsal joint, and

3) moving the CoP to different locations of the foot will cause the midtarsal joint axis to have a new and different spatial location,

then I don't see how we can gain a deeper understanding of this complicated joint by performing an exercise of assuming the constantly moving and changing MTJ axis is now fixed in a stationary location and we are now trying to determine the effects of moving the CoP around that imaginary stationary location of the midtarsal joint.

In trying to determine the kinetics and motion patterns of the hip joint, would you try to assign it a single given axis of rotation? I would hope not. Rather I would think it is more proper to kinetically analyze such a non-constrained joint as the hip by assigning it three reference axes of motion, one in each cardinal body plane, and then determine how a certain isolated external or internal force acting across that joint would kinetically act simultaneously in each of the three body planes.

 

That's exactly what I'm now doing with Michael, Kevin. I've followed your lead and I am using x, y and (at some stage z) axes to model midfoot motion- which is exactly the same as you have done previously in your diagram near the top of this thread. Please re-read the last few posts. For example, if you look at the diagram I had Michael create in post no. 56 we have assigned an "X axis" identical to the one in your diagram, only it is projected onto the transverse plane rather than the sagittal plane.

 

Wouldn't you think it would be easier to understand, for everyone trying to follow along, to use reference axes lying within the cardinal body planes rather than using triplanar spatial locations of axes which may or may not exist at any one time?

 

In classic terms a pronated foot type at this exact time and place in the gait cycle.
It would somewhat mean the foot is anti-phase which ii more stressful on tissue.

Heres what Ive got. I did not include the peroneus longus in the x-axis diagram due to it various points that it influences the motion of the MTJ and STJ , which seemed to work in both in-phase and anti-phase.

red for in phase

Black for anti-phase

Thanks Simon the old head has got a workout though

 

Kevin, I don't see the problem, I'm doing exactly the same as you did in your diagram. In your diagram you had a sagittal plane view of the foot with a dorsiflexion / plantarflexion (we've called this: X, Nester labelled this the Z axis, but given our transverse plane projection of the foot, it makes more sense to label this as X, but if makes people happy to keep to Nester's labelling we'll change it to Z (it makes no difference)) midfoot axis exiting through the talar head. Hence we have merely rotated the view of your diagram to the transverse plane and qualitatively assessed the moments that theoretical COP positions might generate about this axis and a projected subtalar joint axis. We have then added in another orthogonal axis for midfoot inversion / eversion (we've labelled this as Y for the same reason as above; Nester labelled this as X) and repeated the process. Regardless of our differences in labelling to Nester, we are now carrying out the analyses as he, and you have suggested. So, either we should model midfoot axes with a 3 dimensional Cartesian system (the body's cardinal planes) as we have done in the latter posts here (as Nester suggested and you did in your diagram ), or we should model quasi-static to the exact axis location from the best available data (Nester again), as I did previously when I suggested that your diagram was inaccurate. You maintained that your diagram was valid because you were using orthogonal axes. So we have started using orthogonal axes and you're now suggesting it is wrong to do this? We've actually done both. Which method would you prefer us to use?

 

Thank you.

 

Kevin,

Lets go back a step:

1. Do you believe that the forefoot and rearfoot can move either in-phase about the midtarsal joint (i.e. rotate in the same direction) or out-of-phase (i.e. in opposite directions) about the midtarsal joint, as the the reference I provided suggested?

2. If you agree with the proposition that the forefoot and rearfoot can move either in-phase or out-of-phase about the midtarsal joint, how would you explain the kinetics of these in-phase and out-of-phase rotations differently to how Michael and I have attempted to do thus far in this thread?

 

Simon:

I missed your orthogonal axes today while posting notes and seeing patients at the same time and scheduling with my dentist for a root canal.....I think we are cool now.:drinks

 

Multi-tasking hey? I thank you Professor Kirby for making me think I was going mentally round the bend since mid-afternoon today. So, as my mentor, am I barking up the wrong tree, or can we explain in-phase and out-of-phase rotations of the forefoot and rearfoot about the midfoot as I have done?

 

Simon:

There is no reason why it can't be done this way. However, I'm not sure of the biomechanical significance of making such an analysis. Care to offer your thoughts of why you think this type of analysis may be important or clinically significant?

 

BTW, I think this modelling approach might go some way to explain propulsive strategies (i.e. high / low gear)... more tomorrow, too tired tonight.

What it does seem to suggest, taking the orthogonal X and Y MTJ axes that we modelled today, is that if the STJ axis is sufficiently lateral when the COP is heading distal to the midfoot X axis, the forefoot and rearfoot will move in phase, but if the STJ axis is too medial there is greater potential for the forefoot and rearfoot to move out of phase in the Y axis, unless the CoP is really laterally located at this time. Viz. the position of the STJ axis is key, if we model the MTJ in this way. Kirby might have been right on this, but this is a transverse plane analysis and apparently, Kevin's theories are all about frontal plane.... ;-). Me, I just call it as i see it in any plane that presents.

 

In all honesty, I'm really not sure yet. As I only thought of it last night! However, it does strike me that if the foot is moving as one and in one direction this might be more efficient and potentially less stress inducing around the midfoot than if we have the forefoot and rearfoot segments moving in opposite directions. It would be interesting to see if these out of phase movements ( or for that matter, in-phase movements) at the midfoot are associated with pathology- the single ref I listed suggests that plantar fasciitis might be related to out of phase movements- if so treatment should aim to put forefoot and rearfoot into phase in such cases. As ever, I should welcome your thoughts.

Here's the way I look at it: if the centre of pressure position relative to the STJ axis is significant, the CoP position relative to the MTJ axis and the STJ axis has got to be important too.

I'm wondering tonight about muscle recruitment in relation to this....

PS> I seem to remember the foot being modelled as a twisted strip- was it in Sarrafian??? I'll see if I can find it tomorrow.

 

By the way, Michael, congratulations on the new addition to your family. Since I now have three grandchildren, ages 4, 2 and 4 months, and my two sons are now 27 and 22, I really appreciate now how fast time can go when raising children. Here's a little poem for you to put up on your wall as a reminder of how important you are, and will be, to your little boy.

 

Thanks Kevin nice poem , Been a very cool and amazing 1st week of many more to come

This line made me laugh a little - I think thats what my old man wants to happen , so he can sit back smile and say something like ´a beautiful thing life - whats goes around, comes around, goodluck´

 

Correct. Sorry no full text.

PS Doesn´t some other well respected Biomex guy have the same initials as Sarrafian

 

Closed kinetic chain (CKC) pronation of the subtalar joint (STJ) will usually result in relative inversion, abduction and dorsiflexion of the forefoot relative to the rearfoot which is not a forefoot supination motion. The motion of the forefoot on the rearfoot during CKC STJ pronation is constrained by the tendency for the plantar metatarsal heads to remain stable on the ground (i.e. not sliding in the transverse plane) and in a plantigrade position on the ground while the proximal forefoot rotates and translates along with the talar head and anterior calcaneus at the midtarsal joint.

CKC STJ supination will usually result in eversion, adduction and plantarflexion of the forefoot relative to the rearfoot which is not a forefoot supination motion. The motion of the forefoot on the rearfoot during CKC STJ supination is also constrained by the tendency for the plantar metatarsal heads to remain stable on the ground (i.e. not sliding in the transverse plane) and in a plantigrade position on the ground while the proximal forefoot rotates and translates along with the talar head and anterior calcaneus at the midtarsal joint. However, CKC STJ supination is more likely to induce a inversion motion of the plantar metatarsal heads relative to the ground surface than will CKC STJ pronation.

The concept of joint constraint and nonconstraint is another important discussion since the model I am using here and in my papers and books on the STJ aixs is that the STJ is a constrained joint axis that has a relatively fixed spatial location relative to the talus and/or calcaneus, but moves within space during CKC STJ pronation and supination. The best mechanical analogy of a constrained joint that I use in my lectures is to describe a door that is hung on a set of three parallel, aligned hinges that constrains the door to rotate about a certain spatial location of an axis of rotation regardless what the direction and point of application of input force acting on that door. This is a good approximation of the STJ at relatively low loading forces.

However, a noncontrained joint would be more equivalent to having a ball and socket joint, such as a hip joint, where the direction and point of application of the input force would determine the joint axis, rather than the joint axis determining the joint motion. Here is a nice mechanical engineering description of joint constraint, with illustrations, for those of you following along and who want to learn more about constraint and non-constraint of joints, which, by the way, has direct mechanical application to the mechanical design of joint implants for the body. Constraint, Reaction Forces, Moments at Joints

 

So how does this explain the observations of the dynamic studies I referenced earlier, specifically, but not exclusively, the Chang study?

 

I don't know what the "Chang study" is.

 

Post no. 36 in this thread, I'm beginning to think you might not be reading this thread fully, Kevin.

See also:
http://www.jbiomech.com/article/S0021-9290(08)00370-9/abstract

 

Just the important stuff.

 

I thought this statement from Chang was pretty important: "However, anti-phase coordination was not the predominant pattern during mid- or late stance. These preliminary data suggest that the coordinative interactions between the rearfoot and the forefoot are more complicated than previously described." Which is why I'd started to analyse the relationship between STJ axis location, MTJ axis location and centre of pressure position. I think the approach outlined goes some way to explain the observations of Chang. I think this might be important.

 

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