Ankle and midfoot function: interpreting clinical gait data

Gentlemen;

It appears I "caught up" though I will admit I had to "skim" many of your posts.

I will try to keep up and beg your forgivness if I reference something that has already been covered in upcoming posts.
Sincerely;
Bruce

 

Dave

I agree so far with your comments, but have in my mind some contrary evidence which looks at the realtionship between walking velocity and ratio of 1st metatarsal head and plantar digital area 1st toe forces, and using Tony Redmonds paper on disconnect between Hubscher and actual gait movement of metatarso-phalangeal joint. I am trying to dig out refs then check I still have coherent point. I just havent had time to do this yet so you are ahead of me, will try and post this tomorrow if household chores don't get in the way!

cheers

Martin

 

Kevin

I did a quick trial of your experiment yesterday and just having a quick look at the data.

Interestingly during the various maneuvers the force measured under the investigated foot had a range between 20 to 80 of total calibrated weight of 84 kgms. Since I was using a Mat the other foot was not measured so I cannot confirm this but cannot see that this fluctuation was due anyhting but shifting of COM relative to foot rather than any other cause of acceleration.

My problem now is how to represent data meaningfully given the large change in total force being applied to the foot.

My inclination is to express data a ratio of applied rearfoot to forefoot force vs tibial to ground angulations for each of test conditions over measured range.

you can see from attatched graph of one of the manoevers a clear linearity in the force vs time realtionships, I guess at this rate of loading the issue of viscoelasticy is probably minimal.




Given what we are trying to learn about the behavior of the foot and any problems with methods how does this jive with you?

Thinking also about the contribution of the midfoot to this equation. The force under midfoot in this data irrespective of sub-talar joint postion was negligible. Using 5th metatarsal head force as an index of external moments my sub-talar joint on initial examination did appear max pronated at times ( BTW I was subject). I believe that I have a normally stiff midfoot.

Perhaps this is complicating things too much but I feel it would be important attempt to evaluate midfoot separately perhaps looking at rearfoot / midfoot ratios too.

The problem then is how to differentiate midfoot behaviour if the skeletal morphology between subjects is main factor in measured midfoot force, or are other factors also important eg degree of foot motion in frontal and transverse planes.

Cheers

Martin


The St. James Foot Clinic
1749 Portage Ave.
Winnipeg
Manitoba
R3J 0E6
Phone [204] 837 FOOT (3668)
Fax [204] 774 9918
www.winnipegfootclinic.com

 

Bruce:

I know that you and many others use CoM and CoP interchangeably. Unfortunately, this creates great confusion for all of us who are trying to follow along and understand exactly what you are trying to say since the center of mass (CoM) and the center of pressure (CoP) are two very different things. The center of mass is the point in the body where the sum total of masses of the body can be thought to be located whereas the center of pressure is the point on the plantar foot where the sum total of ground reaction force acting on the plantar foot can be thought to be located.

I'm just trying to help all of you become more aware of how important it is to be more precise in your terminology so that all of us can communicate with greater clarity and become more effective at transferring useful information to other individuals.:drinks

 

Kevin

I have started looking at the data for part of your experimental idea.

As I mentioned it is clear that there is a wide range of force applied to the measured foot during a trial.

In Measurement of conventional lunge (measured foot in front) the total force applied to the foot was between 44 and 67 kgs (body wt 84Kg).

To see if normalising the data (I looked at FF/RF ratio vs tib advancement over a single lunge) created an expected result I graphed the results below.






This seems to be what might be expected, and I think might be preferable to using absolute force for comparisons.


any comments?


I need to try and find a faster way to extract data from FMat it is a brutally time consuming process!


cheers


Martin

 

:drinks

Martin:

Nicely done. Now was this testing done with the knee extended or knee flexed? A comparison of knee flexed forefoot to rearfoot GRF relative to knee extended forefoot to rearfoot GRF would be most useful. One could analyze next the maximal slope of the curve, the maximum values of the curve and compare the forefoot to rearfoot GRF at certain angular displacements of the tibia to the ground. Looks like you are on your way to developing a preliminary testing protocol for a larger study that should be publishable in JAPMA.

By the way, the flat portion of the graph is very interesting.....it represents the point at which the forefoot has stopped dorsiflexing on the rearfoot and the rearfoot has stopped dorsiflexing on the tibia and only the forces on the plantar forefoot and plantar rearfoot are changing in response to the heel starting to lift away from the ground at the end of the lunge test. Mathematical quantification of the lunge test......pretty cool stuff, Martin!:drinks

 

Kevin

Thanks for your comments and encouragement. The graph I posted is with measured limb knee flexing and in front of balance limb which is standard "lunge" position and I understand was used was used in study looking at correlation with injury in Australian footballers.

I have not had a chance to look at all the data I collected yet but quick scan gave me impression that this position gave least variation in total force applied which was, in this one trial approx 25% of body weight. I wonder if this is why this postion was used, Iwas always a little curious about that since it doesnt reflect a normal gait alignment. Other conditions measured were with tested limb behing balance limb with knee extended and then with knee flexed. Also I was talking to my clinic pal Simon Fay who is taking an interest in this and he mentioned that when instructing on calf streching technique he recommends jamming the medial column with a thin book under 1st metatarsal head to moderate forefoot abduction and internal leg rotation as anterior ankle moments rise, I added this condition too since it seemed like a interesting possibility.

I intend to try and figure out some way of programing a macro to extract the data from Tekscan software, currently it is time prohibative process and even their research software makes this a clumsy process andwill post results later as time permits.

Dave (or anyone else), if you are still following this post, do you have any experience writing VBA code, I am trying to automate data transfer and calculation from Tekscan to excel, currently this is stetching my programming skills.

cheers

Martin

The St. James Foot Clinic
1749 Portage Ave.
Winnipeg
Manitoba
R3J 0E6
phone [204] 837 FOOT (3668)
fax [204] 774 9918
www.winnipegfootclinic.com

 

Martin:

I would recommend standardizing the lunge tests by having the subject position their trailing foot straight ahead (i.e. no adducted or abducted position) and use no wedges. You may try contacting Tekscan and Norman Murphy, PhD (head of research) to see if he has some solutions for you for data extraction problems. I'm sure if you let Norman know that I recommended contacting him that he will try hard to make your data problems a little easier for you.

 

Mart

.

No I don't, I just use standard tools in Excell, which worked fine for converting big data files from RS Scan to Excel in CSV format.

Regarding your graph, have you used Excel? why is the X scale not linear and what type of setting did you use to produce the graph, line or scatter? wouldn't scatter be best to characterise the data?

Cheers Dave

 

Martin;
can you explain the FF/RF ratio calculation to me, I'm not understanding that aspect of the curve. I think once I understand that I will be able to wrap my mind around the intent or meaning of the curve you have posted.

Thanks.
Bruce

 

Mart

I wrote

It seems I may have mislead you. I have been reading thru my research and notes and it seems that I couldn't extract raw sample data from RS Scan. I did extract the statistical data about certain points of interest eg 1st MPJ start and end time, max force max pressure etc. I did extract convert and analyse sample data from other instruments using MS Excel tho. I was using the scientific soft ware aswell so maybee it's not possible. One would imagine tho that if the software can reproduce graphical charactarizations of data sets then those sets must be stored somewhere. At least as raw voltage data?

I was also going to ask the same question as Bruce about the details of the FF/RF ratio values.

Cheers Dave

 

Dave

Yes this was generated in excel, I used a default template which as you say was not linear on X axis simply to streaighten things out a bit.

I have attatched a scatter plot which I agree is more transparent to data used.

Problem with FMat is that data is output as separate csv for each frame and is formated with extraneous characters which requires a lot of tedious data input, took me about 2 hrs to create this graph from the various data!




cheers


Martin

 

Bruce

My initial idea about using FMat was primary to explore if it would be possible to use the technology some of us are commonly using to better understand the behavior of the foot during second rocker in a more controlled way than we could by trying to measure same period during gait. Also I have been intrigued by the use and meaning of the “Lunge Test” since being introduced to it a lecture by Craig Payne several years ago, since it seemed to offer a more reproducible test than my prior standard ankle DF exam.

Before giving Kevin’s ideas a try what I had not considered was that during the various postures we might adopt to perform a test of weight-bearing ankle flexibility, there might be a wide variation in total force applied across the ankle during a single test and if this would effect threshold at which heel raise might occur. What I had assumed was that heel rise would occur according to combined stiffness of ankle + midfoot, therefore as an index of posterior group contractures it is dubious. However if we could measure contribution of midfoot not only would it be a more accurate reflection of ankle stiffness but also give insight into midfoot behavior.
It is way to premature to start generalizing from one trial but looking at this one set of data it is clear that in this instant, tibial excursion halted well before heel rise occurred. This leads to believe that we may be able to separate out ankle and more distant motion by looking a quality of loading curves.
Because total force applied across ankle seems to fluctuate widely I think it likely that absolute force values may be less important than the force ratios across the ankle when examining ankle flexibility weight-bearing. Because saggital tibial motion is not likely simply a function of measured forefoot ground reaction force when in weight-bearing forward motion, (there is rotational equilibrium, and a balance between internal and external moments applied at rearfoot and forefoot at any instant) perhaps we had better consider the ratios of opposing ground reaction force across the ankle .
Hope this makes since.

As an example of the contribution of the midfoot in some individuals during second rocker have a look at this force/time curve below in a patient I saw this week. This is why I was concerned about your interpretation of that flattened FF curve in your example Bruce. The idea that this is an indication of stalled progression of COM over foot I think may be flawed, in this case it is clearly caused by midfoot dorsiflexion .



Cheers

Martin
The St. James Foot Clinic
1749 Portage Ave.
Winnipeg
Manitoba
R3J 0E6
Phone [204] 837 FOOT (3668)
Fax [204] 774 9918
www.winnipegfootclinic.com

 

Martin;
thank you for the explanation and the examples. I probably did not fully explain my reasoning process for you. While I will still consider your example to be delayed by FnHL, I of course respect the availability of motion / stiffness in the midfoot region.

I understand better what you are explaining adn this is greatly helping me to do the same for myself and for when I work with others. I still feel that your example would benefit tremendously from a 1st ray c/o, and other midfoot stabilization orthotic modifications as well as AJ and midfoot manipulation. But, it would be interesting to see what works best in a step-wise approach!

Thanks Martin!
Bruce

 

I do agree that FnHL may be an issue here. I feel the need to clarify in my own mind better how I much weight I can apply to the evidence I perceive. I would like to start another thread later on the issue of the transition into 3rd rocker and particularly direction and velocity of COP which has been suggested as a measure of compensation for FnHL. I feel I have quite a bit to sort out on this 2nd rocker issue yet and still have some questions/ideas I would like to post when I get time. I am just doing a batch of reading right now to fill in some knowledge gaps.

I want to anotate that last batch of curves and see if there is any agreement on a qualitative assessment of it, will post later.

BTW I did go and read Perry's chapter on normal knee function and could not find any indication that upto 5 degs of knee flexion through stance was abnormal. Also I cannot recall ever reading this other than intro texts which talk about basic tenents of normal walking gait requiring knee to be extended during stance. Perhaps we should be considering 0-5 degs normal, I am not sure that without using 3D and markers we could evaluate accurately outside that margin of error anyway. How much knee flexion during stance do you estimate to find abnormal?

cheers

Martin

 

Martin and Bruce:

Please explain what you mean by "up to 5 degs of knee flexion through stance was abnormal". During walking, it is generally accepted that the knee is very close to fully extended at heel contact with knee flexion occuring during contact/early midstance to help absorb shock. Then the knee will extend to become nearly fully extended at heel off to then rapidly flex again during propulsion. Therefore, the knee flexes both in early stance and terminal stance phase during walking. Unless you specify which phase of stance you are speaking about here, we will all become lost and confused in trying to read and understand your discussions.

 

Kevin

Perhaps the origin of my comment has been lost except to Bruce and myself.

Bruce mentioned seeing knee flexion during 2nd rocker as compensation for elevated ankle stiffness and treating this via prox tib/fib joint manipulation and seeing change in FTC which he interpreted as result of subsequent improved compliance.

I then questioned how Bruce felt the abnormal knee flexion during this period was characterised since, as you say, knee flexion has been shown to be normal during this phase, quoting Perry as my reference.

So we have been talking about 2nd rocker all along, not stance phase, I guess we assumed wrongly that this was obvious.

Seems like you were off our rocker this time Kevin . ....... geeze . . . . . .. .sorry about the pun but it was a rare opportunity

cheers

Martin

 

Martin;

I will readily admit that I don't make an angular calculation, but look instead for perceived extension of the knee. I would not argue with 0-5 degrees as being normal I suppose. It would probably reassure me to do some angular calculations on the patients I work with, so I guess I need to put up and do that on my next few studies.

I look forward to your thoughts on the 2nd and 3rd pivots and the transition period between the two. It should be a very interesting discussion.
Thanks
Bruce

 

Martin adn Kevin;

Grrrroooooaaaannnn - re: the above pun!:dizzy:

I would consider the second rocker which encompasses AJ and Midfoot DFion ROM to be pure stance phase - early to late.

I think that Martin or I may have mistyped when referencing 0-5 degreees of flexion during stance being abnormal. I would grudgingly consider that ROM to be normal during stance, not abnormal.

Bruce

 

Martin:

Stance phase is when the foot is on the ground and swing phase is when the foot is off the ground.....does 2nd rocker occur during swing phase then?? :bang:

 

Sorry Kevin I dont get your point, 2nd Rocker is a portion of Stance phase, I understand that you are refering in your comment to the entire stance phase, I was refering just to that portion of it called 2nd Rocker.

Is this a problem with understanding our terms or less likely do we really have a basic disagreement about the phases of normal knee extension/flexion?

cheers

Martin

 

Martin:

Honestly, I'm trying hard to follow your discussion but find that I am continuing to be confused by what you are writing. Normally, you are very clear in your writing style.

You said earlier, "So we have been talking about 2nd rocker all along, not stance phase, I guess we assumed wrongly that this was obvious."

Then you said above, "2nd Rocker is a portion of Stance phase."

Now, Martin, read those two statements a few times and ask yourself if possibly there might be many of us who really don't understand what you are trying to say here. I believe that, if I am interpreting you correctly, you should have originally stated "So we have been talking only about the 2nd rocker part of stance phase all along, not about the whole stance phase, I guess we assumed wrongly that this was obvious."

Normally, if this discussion involved more than just a handful of contributors here on Podiatry Arena, I would not comment anything and would simply discontinue reading this thread and ignore it. However, since I perceive you to be an individual that is trying hard to learn and communicate your thoughts clearly to others, and you have made some marvelous contributions here on Podiatry Arena, then I am taking the time the point out a few problems that I am having (and likely others are having) in trying to follow your discussions on this subject.

I know of quite a few others here on Podiatry Arena that I have made these same types of comments to in order to enable them to become better communicators with the written word. Writing with greater clarity and less ambiguity are skills that are learned by constant practice and you are doing a great job otherwise.:drinks

 

Kevin

OK fair comment and thanks. Over the years I have noticed how easy it is to become so imersed in an idea and assume that those who I am talking to about it have the same train of thought. I find it a little difficult sometimes to keep a balance between feeling self consciously pedantic and actually making sence.

:drinks

Martin

 

Martin:

My rule of thumb is to spend the extra time making things extremely clear and detailed to ensure that the people I am trying to communicate with completely grasp my meaning rather than to be so brief and ambiguous that others will have to guess what I am trying to say.

 

In consideration of further interpreting the subject/step I used post #53 which represents data for a subject with a single step (made using 2 step method) over a Tekscan FMat, equilibrilated across at 0.5 kg/cm2 intervals and range 0-5kgms/cm2 and calibrated using single step method.



I made a speculative interpretation of abnormal midfoot dorsiflexion during 2nd Rocker based on; elevated mid foot peak pressures and force/time integrals, delay in heel rise, shapes of heel and forefoot loading curves.

I have re-masked this step in more detail and wanted to see how others might see the inferences/assumptions listed below.
1 the blue segment largely measures ground reaction force beneath cuboid
2 in a “normally” functioning foot ground reaction force would less under the cuboid than 1st metatarsal head.
3 Because of rigid coupling between navicular and cuboid they are regarded as a functional unit and therefore ground reaction force beneath cuboid may be used as an indirect qualitative indication of mid tarsal joint behavior.
4 Excessive ground reaction force measured beneath cuboid during stance may be caused by structural derangement of midfoot (eg Charcots) or excessive dorsiflexion moments around navicular cuneiform joint (NCJ)
5 At the end of 2nd rocker there should be ground reaction force detectable under the hallux because excursion of the medial longitudinal arch will load the hallux via tension of the plantar fascia.
6 Loss of signs of ground reaction force under the hallux (without signs of mechanical derangement) at the end of 2nd rocker could ONLY be explained by recruitment of hallux extensors, extensor contractures, forefoot inversion and/or an extremely compliant plantar fascia at beginning of its strain.
Cheers

Martin

 

Martin

I can see some useful info coming out here

Cheers Dave