Midtarsal Joint Equilibrium Theory

In this post where I listed Nester et al papers re midtarsal joint http://www.podiatry-arena.com/podiatry-forum/showpost.php?p=168235&postcount=21

In the Kinematics of the midtarsal joint during standing leg rotation, they wrote

Which make Kevins always well be always

But if we use the cardinal body planes as referrences ( which we had some discussion about earlier in the thread) then always it is not.

What I´m having trouble with is we are discussing motion ie in-phase and anti-phase motion not position.

So when we have motion we discribe motion in a body plane

when we discribe position it must be relative to something. ie inverted relative to the heel.

Now I get the apples and apples and oranges discussion and the importance to see what Ryan used to see if it apples or oranges.

but say the forefoot was inverted 8 degrees to the rearfoot and the rearfoot everted and the coupling effect ment the forefoot everted to 2 degrees inverted relative to the heel we would have have in-phase motion but the forefoot is still inverted relative to the heel.

ie cardinal body plane motion , position relative to...

this make sense to me is it wrong?

 

Read again what Nester wrote, what they were saying was that the forefoot moved in-phase with the rearfoot, not as Kevin maintained that the forefoot and rearfoot should "always" move anti-phase. With external rotation of the tibia, would you expect the rearfoot to invert or evert? Invert right, providing it's coupled. So with external rotation of the tibia, Nester noted inversion of the forefoot. If forefoot and rearfoot were moving anti-phase, I should have expected the forefoot to evert in response to the external tibial rotation. This was not observed.

Now as Jeff, pointed out we do not know whether there was a 1:1 ratio between forefoot and tibial or forefoot and rearfoot motion. But we can hypothesise that the rearfoot and forefoot segments were both everting with internal tibial rotation and both inverting with tibial external rotation.

 

And if we look at table 1 in the Kinematics of the midtarsal joint during single leg rotation we only see positive values which means in-phase motion.

Does that just means Kevin was wrong with the always ?

Craig we need a new smilie a guy waving a swedish flag who´s head just exploded

 

It means we have to be clear with our terminology.

 

Aye matie!:sinking:

 

Take a look at the description of stance phase mtj motion as described by Root, Weed, and Orien which begins on page 139 of Normal and Abnormal Function of the Foot. Essentially they say that when the mtj pronates about the oblique axis, it supinates about the long axis. What they actually mean is that the forefoot abducts and dorsiflexes (i.e. oblique axis pronation) while the forefoot simultaneously inverts (i.e. long axis supination). So the third option is the when the stj moves during closed chain pronation and supination, the mtj neither supinates nor pronates. In other words, the mtj can't simultaneously supinate and pronate about a single axis of motion, so the closed chain triplane motion that occurs at the mtj is neither supination nor pronation. Therefore, it is neither in-phase nor anti-phase motion if these terms are intended to describe motion that is equal or opposite to supination or pronation of the stj.

Jeff

 

Jeff, I explained this observation at the start of this thread. Using a single axis model there are axial positions were pronation and supination of the MTJ may occur, but there are also axial positions which are derived from movements which do not fall into the same pattern, as you highlight above. If we take a planal (X, Y, Z) approach to the MTJ, we can say, for example, that the frontal plane movement is in-phase between the forefoot and rearfoot, but the transverse and sagittal plane motion is anti-phase, etc.

 

Re: Competing Theories in Podiatric Biomechanics Seminar

The big difference between the midtarsal joint and the STJ in using center of pressure is where the physical joint is in relation to the forces. In the STJ the center of pressure is acting entirely on the distal side of the joint as the talus does not touch the ground. On the other hand, at the midtarsal joint the forces that sum to create the center of pressure are on both the distal and proximal sides of the joint. So, to calculate moments about the MTJ you would have to take into account forces not in the diagram e.g. the force of gravity acting on the body.

An analogy is looking at center of pressure when you have your leg and foot on a cushy foot stool. Think lateral side of the foot and leg on the foot stool. You can calculate a center of pressure for the leg and the foot, but it wouldn't create any moment at the STJ. You would reach an equilibrium position of the STJ and just sit there.

So, you can't calculate moment from center of pressure relative to a joint axis if the center of pressure is summed from forces on both side of the joint.

Cheers,

Eric

 

Re: Competing Theories in Podiatric Biomechanics Seminar

Eric,

Does the foot have a net ground reaction force vector acting upon it during gait? Surely, if it does this vector has a centre of pressure, this net ground reaction force vector will be acting in relation to the joints axes whether one segment, no segments, or both segments are in contact with the ground. But now you've got me thinking about the elbow...

In the case of the talo-navicular joint neither the talus nor the navicular are in direct contact with the ground, similarly if we look at the hip joint, knee joint or ankle joint neither the proximal nor distal segments of these joints are in direct contact with the ground. So presumably we cannot look at the net ground reaction force vector to determine the external moments acting across the hip, knee or ankle joints either? Moreover, your contention suggests that the force of gravity acting on these joints needs to be considered separately also? Isn't the ground reaction force in part due to the acceleration due to gravity?

In the case of the calcaneo-cuboid joint, only the calcaneus is in contact with the ground, so by your reasoning, this should be valid- right?

In the case of the metatarsophalangeal joints ground reaction force may act at both the metatarsal head and the proximal phalanx, you said "you can't calculate moment from center of pressure relative to a joint axis if the center of pressure is summed from forces on both side of the joint", so by your reasoning we cannot calculate the external moment acting about a metatarsophalangeal joint?

You going to need to help me out here, Eric as your contention seems to suggest that centre pressure location is meaningless for the majority of the joints of the foot.

 

Some thoughts on this thread.

I'm with Kevin on having a time seeing an application for the use of joint axes for the midtarsal joint. That's not quite what he said, but I'm still having a hard time seeing the application. Yes, the joint axes describe the motion, but I don't think it works for calculating joint moments. In my most recent post in this thread I explained why you can't use cop to calculate joint moments at the MTJ. I think it is much more effective to do free body diagram analysis. Using free body diagram analysis you can estimate forces in anatomical structures. There are no anatomical structures that correlate with the measured midtarsal joint axes of motion. In the STJ, the motion is constrained by the joint surfaces that are held close together by ground reaction force/body weight and the ligaments of the joint.

So ground reaction force under the heel and forefoot, in conjunction with the inertia of the body, or body weight, will tend to dorsiflex the midtarsal joint to its end of range of motion (when the plantar ligaments become taught. [increasingly stiff]) At any instant in time, you could take the center of pressure of just the met heads and toes and calculate the dorsiflexion moment by taking the distance from the forefoot center of pressure to the joint. The resistance to that dorsiflexion moment will have to be provided by tension in plantar structures and compression of the joint surfaces.

What say ya'all

Eric

 

Re: Competing Theories in Podiatric Biomechanics Seminar

Time for a quick answer.

The think I did not make clear in my other post was that there is a difference between using the center of pressure for the entire foot or just a portion of the foot. You can calculate the dorsiflexion moment at the 1st MPJ if you use the center of pressure of the anatomical structures distal to the joint.

Eric

 

Re: Competing Theories in Podiatric Biomechanics Seminar

I think you are going to need to expand on this, Eric. Lets take the ankle joint, say we wanted to look at sagittal plane moments acting about the ankle joint axis. Lets assume the ankle joint axis is perpendicular to the sagittal plane. And so we make a sagittal plane drawing of the foot and lower leg. We can draw in a ground reaction force underneath the heel acting proximal to the ankle joint axis, we can also draw a ground reaction force acting under the metatarsal heads acting distal to the ankle joint axis.We can draw in the position of the ankle joint axis. Are you saying we cannot calculate the centre of pressure for the forces and the net moment for these forces acting about the ankle joint axis in the sagittal plane? Now, lets take another sagittal plane view of the foot and the MTJ X axis, lets assume, as we did for the ankle joint, that this axis is perpendicular to the sagittal plane and draw another diagram this time replacing the ankle joint axis for the MTJ X axis. In an identical fashion to the ankle joint axis, ground reaction force will act proximal to this axis underneath the heel and distal to this axis under the metatarsal heads. Can we calculate the centre of pressure for these forces and thus the net moment on the MTJ X axis,? Your previous post suggests that neither of these analyses are possible. Yet I know that you have written about this type of analysis for the ankle, so what's the difference?

 

If the joint axes are derived from the motion and the motion is occurring due to a net moment acting about the joint axes (we can't have one without the other- right?), why can't we calculate moments about the instantaneous axes and the forces producing them? Alternatively, if we are to use the X,Y,Z approach to the MTJ axis, as is Kevin's preference, surely we should be able to calculate moments about these axes too?

At the moment I don't agree with your explanation as to why we can't use centre of pressure to calculate joint moments at the MTJ, but I'm willing to learn and to hear you develop you arguments to support your contention, please go ahead and answer my questions regarding a sagittal plane analysis of the centre of pressure acting about the ankle joint axis and the MTJ "X" axis.

I'll be more than happy to talk about free-body analyses once we have resolved the issue of centre of pressure. I will say this though, you appear to be assuming an anti-phase motion between the forefoot and rearfoot in you post above:drinks

 

Re: Competing Theories in Podiatric Biomechanics Seminar

Yes, you can calculate moment from CoP in the above situation. It appears that we are having a bit of difficulty with the definition of proximal and distal. My earlier statement was that you cannot use CoP to calculate moment when the CoP is summed from forces both distal and proximal to the joint axis. In the example above you can interpret distal in two ways. The first is that in stance pressure on the heel is proximal to the ankle joint axis. However, my statement should be applied to the anatomical joint (tibia and talus articulation) and not the axis. The forefoot and heel are both distal to the anatomical joint, but they are on either side of the midtarsal joint.

You can do the calculation, but does it provide the information that you want? If you want what direction will the MTJ move in response to the forces applied (including body inertia/body weight) then you would not get the answer you want. (When you apply force to the plantar foot, the tibia will apply a downward force to the talus.)

The the effect from a force applied at the center of pressure can be replicated in a seated person with the foot pointed toward you. This is how Kevin's palpation of the axis works. You could use two fingers, apply equal pressure with both fingers and the center of pressure from your fingers would be halfway between your fingers. You can still find the STJ axis with two fingers just as if you were using one finger.

Now try the single finger push while thinking about the MTJ. If you push proximal to the axis you described, you get dorsiflexion of the ankle, but no plantar flexion of the MTJ. Well, you might get plantar flexion becasue ankle dorsiflexion may cause an increase in passive tension in FHL. There would not be a direct effect from the applied force.

Now try the two finger push test. Put the average of the two fingers proximal the axis you described. (I'd recomend a finger on the heel ~ 5cm behind axis and the other finger 3cm in front of MTJ "axis". With the calculation of moment from center of pressure you should get plantar flexion of the joint. However, both fingers are applying an upward force and you get dorsiflexion of the MTJ.

Hope this helps,

Eric

 

You can calculate a moment about any axis you want. The question is whether it provides you with valid information. David Winter used an example of calculation of moment about the neck from ground reaction force vector. Yes you can calculate the moment, but it not give you a result that provided any useful information.

I don't see why it matters what I assume about phase/ anti phase motion. This is only used for the determination of the location of the axis. I'm saying that if you apply forces to both sides of the joint, the center of pressure location won't matter.

Eric

 

Simon and Eric:

The moments acting across the subtalar joint (STJ) can be realistically modelled by using center of pressure (CoP) by assuming the foot is single rigid body about which CoP acts and all of the ground reaction force (GRF) is acting distal to the STJ, not proximal. However, in the case of the midtarsal joint (MTJ), GRF acts both proximal to the MTJ (i.e. on the plantar calcaneus) and distal to the MTJ (i.e. on the plantar forefoot), with the rearfoot GRF vector and forefoot GRF vector each independently affecting the kinetics of the MTJ.

Therefore, if we knew the direction, line of action, point of application and magnitude of the GRF vector acting only on the plantar rearfoot and also knew the direction, line of action, point of application and magnitude of the GRF vector acting only on the plantar forefoot, and we could also effectively model both forefoot and rearfoot as each being rigid bodies, then we could better determine the external moments acting at each of the three reference axes of the MTJ. Unfortunately, using a combined CoP value (that averages both the forefoot and rearfoot GRF) to calculate the external moments acting across the MTJ will generally not be useful, unless, or course, either the forefoot or rearfoot is not bearing weight on the ground, such as during early contact phase or during propulsion.

That's the way I see it.

Great discussion! :drinks

 

This is the key and the error (limitation) in my analysis of the MTJ, I too have assumed the foot is a single rigid body. Equally though, if we were talking about a centre of pressure position which was distal to the MTJ, then the single rigid body approximation of the foot for determination of STJ moments would appear erroneous. Which is why if you move too distal along the plantar foot when trying to palpate the STJ axis it gives spurious results.

Agreed.

Eric, Kevin:

Lets say we have a foot during gait moving from forefoot loading through to heel off and we model the MTJ as having three Cartesian axes X, Y and Z as before.

The external moments acting independently at the forefoot and rearfoot will tend to move the forefoot and rearfoot in opposite directions (i.e. antiphase motion) until equilibrium about each axis is achieved. For example, in the case of the MTJ X axis the external moments would tend to cause rearfoot plantarflexion and forefoot dorsiflexion and this will continue until the internal structures generate equal and opposite moments- agreed?

Now, if the internal structures generate moments acting upon the forefoot and rearfoot which are opposite in direction but of greater magnitude than the external moments acting about the forefoot and rearfoot, the motion will decelerate (there will be an instant of equilibrium) and reverse reverse with the forefoot plantarflexing and the rearfoot dorsiflexing (again resulting in anti-phase motion between the forefoot and rearfoot)- agreed?

So in order for the forefoot and rearfoot to move in phase, there must be equilibrium between the internal and external moments acting about the joint axes. Now, what if during this period of gait, equilibrium about each of the MTJ axes, X, Y and Z did not occur simultaneously at the same instant in time? Lets say equilibrium is achieved first around the Z axis (transverse plane motion) then around the Y axis (frontal plane motion), then finally around the X axis (sagittal plane motion). How would this influence the movement pattern observed between the forefoot and rearfoot? Once equilibrium is achieved around the Y axis say, could we then use a single CoP to model the external moment acting about this axis, since the forefoot and rearfoot are now effectively a rigid body in the frontal plane and moving in-phase even though the forefoot and rearfoot are not in equilibrium in the other planes (although, I can't see the use of this)?

Hope that makes sense.

 

Before we go any further regarding "in-phase" and "anti-phase" motion of the forefoot, what is your defintion for forefoot motion? Is this forefoot to ground motion or distal forefoot to proximal forefoot motion?

 

I think there are lots of definitions of forefoot motion. In the example above I used distal forefoot to proximal.

 

I think it may still work even if the foot is a non rigid body. This is an area where I have not read much, but thinking about free body diagram analysis you can make the case: when you push on a non rigid body, and it pushes back, the force will eventually create a moment about an axis. A good example is pushing upward on the first met head when trying to palpate the location of the STJ axis. In an extremely medially deviated STJ axis, you will see the STJ pronate and the first ray dorsiflex simultaneously. The reason this happens is that there is a proximal counter force from inertia/body weight.

(Newton's second law F=ma. When a force is applied it will accelerate unless there is a force of equal magnitude in the opposite direction. So, if the non rigid body is not accelerating, then there is a force from both directions. So you should not expect the location closer to your finger to move first. The joint with the greatest net moment will move the most.)

agreed

Eric

 

When you push on the distal forefoot, close to the axis the movement of other joints makes it difficult to appreciate the exact location of the axis. Theoretically, you should be able to assess it.

This seems like a long way of saying that joint(s) will move in the direction of net moment. Also, when you say equilibrium has been achieved you need to assess how stiff the structures are at that equilibrium point. For, example muscles have a variable stiffness. If the muscle stiffness changes, equilibrium is lost.

Eric

 

I think this is similar to one of the points I was trying to make with my example above. At some point the "slack" in the system is taken up as the joint segments reach end of range or the internal moments create stability (increase joint stiffness). In your example of pushing on the 1st MTP, first in the chain we get dorsiflexion moment on the first met head and presumably plantarflexion at its base until equilibrium with the internal moments acting at the 1st met-medial cuneiform joint is reached, then we get motion of the medial cuneiform on the navicular at the navicular- medial cuneiform joint until end rom, then navicular motion at the talo-navicular joint joint.....

 

Yep, and then the forefoot and rearfoot will move anti-phase again. I'm trying to nail why the forefoot and rearfoot might move in-phase in some individuals and anti-phase in others. Or why the forefoot and rearfoot might move in phase in some individuals at certain times but not at other times. I thought if any one would get a handle on this it would be you Eric, which is why I was pleased when you started contributing to this thread.

 

I think you get my point, but I'd like to add that the "slack" doesn't have to be taken up in a distal to proximal order. For example, if instead of pushing on the head of the metatarsal you pushed on the shaft in a very medially deviated STJ axis foot, you may see pronation of the STJ before you notice first ray dorsiflexion. Another example is pushing upward on the second met head that is slightly lateral to the STJ axis. You will notice the more "proximal" ankle joint move before the STJ moves because your force creates a greater dorsiflexion moment than STJ pronation moment.

Thanks for the appreciation.

Eric

 

Jumping on a step (rightly or wrongly): if anti-phase forefoot to rearfoot motion occurs when the external moments are not exactly equal to the internal counter moments and if in-phase forefoot to rearfoot motion occurs when the internal and external moments are in equilibrium, this means that we can achieve anti-phase motion with either lower internal moments than external moments, or lower external moments than internal moments. If we accept Kevin's contention that anti-phase motion is the preferred movement pathway through midstance, then we might also say that higher external moments than internal moments should be the desired method of driving this motion, since this should result in a lower metabolic cost and lower tissue stress. Ryan Chang reported to us that he had found increased in-phase motion in patients with plantarfasciitis. Is this because that to walk with an in-phase forefoot to rearfoot movement pattern the internal moments must be relatively increased to match the external moments, thus, raising the stresses within the tissues? Or, is in-phase motion purely the result of a guarding response to the existing pain and pathology? Either way, I'd like to know how in-phase and anti-phase motion of the forefoot and rearfoot are driven. I feel I'm moving closer to understanding this through our discussions here.

Or, is it because the in-phase motion reported by Chang was occurring prior to forefoot loading or after heel lift? In which case my previous analyses of the centre of pressure and net ground reaction force vector acting about the STJ and MTJ axes may still be a valid explanation.

Just thinking out-loud. All yours Eric and Kevin. And indeed, Ryan (where you gone?)

 

In which case the 1st met cuneiform joint must be relatively stiffer than the next joint etc.

If I have some blocks on the table connected by string and I pull up on the string attached to the last block in the chain, if the string connecting each block is the same stiffness they should lift off the table sequentially starting with the one attached to the string I'm pulling on, but what if we replaced some of the string connections with wire and some with steel rods?

Thinking about it, the length of the blocks (skeletal segment lengths) and the distance between the blocks (joint space) will be important too, along with the shape of the blocks on either side of the string (articular geometry), but you get the point: the joint with the lowest stiffness will move more for a given load than a joint with a higher stiffness.

 

Simon:

Good. This is the definition I prefer since it is consistent with the way we define motion at other joints of the foot and lower extremity. Now we may proceed.

 

Eric:

The rigid body description of course is only an approximation but is necessary to model these segments and then make mathematical assumptions about their moment of inertia, center of mass, etc. Unfortunately, a deformable body, which is also a "non-rigid body" as you described above, may undergo no motion as a unit when acted upon by an external force but may, instead of moving as a uint, will simply deform at the point of application of force (imagine a ball of soft dough). Therefore, if we want to model how external forces act in foot segments in a simplistic fashion, then the rigid body assumption is a necessity, unless we want to get into modelling the time-dependent dynamics of deformable bodies, which is beyond the scope of my knowledge.

 

If Ryan Chang's forefoot motion is defined as distal forefoot to proximal forefoot motion, then I totally agree with your analysis that the in-phase motion is a guarding response to the pain when an individual has plantar fasciitis, since anti-phase motion of the rearfoot to forefoot would be the expected normal response of the foot during midstance.

Agreed. I have enjoyed our discussions here with you and Eric since I haven't thought this much about midtarsal joint kinematics and kinetics since I wrote that series of newsletters on the subject back in 2001 (Kirby KA: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002.) Eric and I did write something about midtarsal joint rotational equilibrium in our chapter that we wrote five years ago and hopefully someday will be published, but we discussed more about kinetics than kinematics of the midtarsal joint.

The functional importance of midtarsal-midfoot function should not be minimized since foot orthoses certainly have much better mechanical advantage at affecting the kinetics and kinematics of the midtarsal joint than affecting the kinetics and kinematics of the subtalar joint. The definitive paper hasn't been written on this subject yet and it is long overdue. Understanding midtarsal and midfoot function is of huge importance to describing not only the mechanics of the human foot and lower extremity, but also to understanding the mechanically-related pathologies that affect the locomotor system of the bipedal human.

Onward and upward!!:drinks

 

Re: Competing Theories in Podiatric Biomechanics Seminar

Thanks for this Eric - makes alot of sense. Sorry for going back abit had a day with a group of physios yesterday discussing biomex and took me awhile to catch up, if Its ok to join in.

While I see what your saying re COP Ive a question related to GRF and the use of force plates - re the next step of the discussion and the body diagrams you three have been discussing might it not be good to know where the GRF is coming from in relation to the x,y and z MTJ axis and the strength of the vector ? or ?

ps I tried to email Ryan through PA to ask where and how he measured motion of the forefoot but no response as yet

 

Re: Competing Theories in Podiatric Biomechanics Seminar

This is the marker set he referenced:
http://www.tsb-web.org.tw/isb2007/isb2007-paper/ISB/0266.pdf

 

Kevin, Eric
The questions are these:

1. Does in-phase forefoot to rearfoot motion occur as a normal variant during gait?
2. What are the differences in the kinetics of in-phase versus anti-phase forefoot to rearfoot motion?
3. Is in-phase motion the result of pathology (i.e. a guarding response), or is it the cause of pathology?
4. Am I correct in my assumption that as long as equilibrium between internal and external moments across the MTJ axes are maintained then the forefoot and rearfoot will move in-phase about the MTJ axes?

 

Simon:

In the short amount of time I have now to answer these questions (getting ready to go to San Diego to lecture on "Biomechanics of Flexible Flatfoot" and "Biomechanics of First Ray Function"):

1. Probably more during contact phase and propulsion, and less so during midstance.

2. In-phase kinetics will be contrary to the ground reaction force produced moments during midstance.

3. Don't know.

4. You are incorrect in this assumption since if equilibrium was truly maintained during gait, then no accelerations or decelerations of motions at the midtarsal joint could occur.

 

I probably shouldn't have said "move in-phase about the MTJ axes" and rather should just have said that the forefoot and reafoot will move in phase when the moments about the MTJ axes are in equilibrium,

But this is the point of key interest for me. If the forefoot and rearfoot are moving in-phase (and given Ryan's, vector angles I think he may define in-phase motion as the forefoot and rearfoot moving in the same direction and at the the same speed (i.e., a 1:1 ratio), how is this achieved kinetically? My best guess is via equilibrium at the MTJ, i.e. the rearfoot and forefoot are functioning as a rigid body. How else is this achievable?

If there was equilibrium about the MTJ axes then both the forefoot and rearfoot segments could move in-phase with a constant velocity with no accelerations or decelerations between the segments- right? But a 1:1 ratio could only be achieved with equilibrium of the forefoot and rearfoot segments about the MTJ- right?

If we forget the 1:1 ratio for now, how else might in-phase motion be achievable? In other words can you explain how the rearfoot and forefoot segments might move in the same direction during midstance when the moments acting about the MTJ axes are not in equilibrium? Lets say both rearfoot and forefoot were inverting simultaneously, there just has to be a net inversion moments acting independently on the rearfoot and forefoot at the same time, the MTJ moments might not be equilibrium though in which case one segment will accelerate more rapidly than the other but both will move toward further inversion? In which case though one segment (either forefoot or rearfoot) could reach equilibrium before the other and then the motion would be anti-phase again until the other segment reached equilibrium.

Good luck, enjoy the meeting. Send my regards to Don.

P.S. we really need some more input from Ryan. I don't think anyone can be accused of being less than welcoming to him here at the Arena, he seems to have decided for himself not to continue to contribute to this thread.

 

Simon:

I understand your reasoning. However, I'm not sure that the forefoot can easily move "in-phase" with the rearfoot in all three cardinal planes, especially during midstance. However, during contact phase and propulsion, in-phase motion of the forefoot and rearfoot would be expected to be more likely, especially if the forefoot motion was referenced to the ground and not referenced to the rearfoot.

I'll let Don know that you said hi. I'm leaving in the AM for San Diego.

 

I don't think that it is possible to infer phase motion from traditional time series. This is why we proposed this method.

I used the Leardini marker set. In the 2007 paper, we used the reference frame that he describes. The tracking markers include all 6t markers on the forefoot. For my more recent work, I continue to use the Leardini marker set, but split the forefoot in half - medial and lateral. the reference frame is located on the base of the first metatarsal. It would be a bit lengthy for me to describe how the reference frame is created.... I agree that reference frames are important.

 

I used a forefoot to rearfoot convention. HOWEVER, please keep in mind that the motions are first computed relative to the global reference frame, then forefoot to rearfoot. We must compute then to the global frame first to get at the phase relation.

 

Nope, call me thick, but you're going to have to explain as I don't understand, Ryan. Indulge me with your lengthy explanation, please.

Is in-phase motion classed as only occurring when you see a 1:1 ratio between forefoot to rearfoot motion?

Is forefoot motion on rearfoot motion, proximal forefoot or distal forefoot?

Does in-phase forefoot to rearfoot motion occur when both the forefoot and rearfoot are in contact with the ground, or only when one of the two segments are in ground contact?

If yes to the above question, can you explain the kinetics of in-phase forefoot to reafoot motion when both the forefoot and rearfoot are in contact with the ground?

 

Hi Simon,

These issues are described in the paper. I'd be happy to send you a copy. What is your email? The computations are derived from an angle-angle plot of the segment angles (not joint angles). Computing the vector angle is what determines the coupling. e.g. a 45 degree coupling angle is 'purely' in-phase. We set a tolerance for that however... in this case we did 45 degree bins. Which means that 45 +/- 22.5 degrees is considered in-phase. I think once you see the figures it will make much more sense.

Hope this helps.

 

Hey Ryan....send me a copy of your paper also....kevinakirby@comcast.net.

Also, don't leave yet since I agree with Simon....this stuff is somewhat confusing to me also. However, I really feel your research may be important for me, and many of the rest of those following along, to better understand normal and abnormal midtarsal joint function.

Thanks for taking the time to answer our questions, Ryan.....guess I owe you a beer next time we're out at a seminar.:drinks