The "Midtarsal Joint"...

Sorry that I don't have a lot of time right now to give a lengthy description. However, to give you a brief summary, by using the idea that the internal resistance that is encountered when attempting to dorsiflex the forefoot to the rearfoot is a measure of forefoot dorsiflexion stiffness, the forefoot dorsiflexion stiffness would be able to used as a mechanical concept that would allow us to better understand how the foot can both be a "mobile adaptor" and a "rigid lever" during weightbearing activities. The magnitude of forefoot dorsiflexion stiffness is modulated both by the passive mechanical effects of the plantar ligaments and plantar aponeurosis and by the active mechanical effects of the deep flexors, peroneus longus and plantar intrinsic muscles. In this way, the individual may "regulate" forefoot dorsiflexion stiffness via the central nervous system to optimize the weightbearing mechanical characteristics of the foot.

 

Do you have to have an acount with Rx labs to view this. I got the message we cannot locate the article you requested.

 

Try:
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Eric,

Sorry, wrong link! Try:
http://www.rxlabs.com/articles_listArticles.asp

 

sorry to get in this so late...Keiv K. you wrtote:QUOTE=Kevin Kirby]Good point, Simon. Since we know that the navicular and cuboid do not move as a solid rigid unit (i.e. we know there are some slight movements between the two bones), then the one axis model of the midtarsal joint is an approximation of reality, but not absolute reality.

Why do you think that the cuboid and navicular have movement.....I mean, if the foot is not weight bearing, I can see it, but as soon as the lateral column bears weight, the cuboid rotates the lat cun into the notch between the cuboid and naviculaar effectively loccking it....the thre bone act as one....this is what gives you the single axis. If you recall, over two years ago I was saying this and saying that the axis was long the longitudinal axis of tha lateral column. Were you speaking of non weight bearing?

 

http://www.podiatry-arena.com/podiatry-forum/showpost.php?p=7495&postcount=20

 

Re: More on the MTJ

Dear All

Funny to read that a study would use MRI when the best it can slice is 3.0mm where a good CT scanner can slice at 0.3mm ie ten times more slices per distance.

Many people think that an MRI with its great pictures actually has a better resolution that CT. It is simply not true.

With some systems the Software is better with CT than for 3D imaging.

I can say that Having used MRI and CT images for 3D an MRI is a bit like an old black and white TV versus a Plasma screen. MRI in 3D just misses too much.

I cannot see how they got such clear information without a very skilled operator using extremely expensive software.

Musmed
www.musmed.com.au

 

Hye Paul...nice to hear from you. Hope everyone appreciates what you are saying about .3mm slice CT. Having seen it mysself, I am amazed.

Now for Simon...you wrote:How many degrees ROM do we need before 2 objects cannot be considered as a rigid body?

Damn good question. The problem is plastic deformation of ligamentous strunctures. Have you ever heard of an intercuneiform ligament? I had not until I dissected them out....then I found only 3 references and one was in french. If the ligaments aren't plastically deformed, then the mechanism I described works. I have seen it in the laband will show up on one of the mythical papers I promise. However, when the ligaments are stretched, there is ALWAYS some slack. So, is the movement measured in your studies "real" in the sense that it is supposed to be there, or is is plastic deformation of supporting soft tissue structures? I haven't answered the question to my own satisfaction yet...I doubt many have thought of it this way. Ask Paul though, with his fancy equipment, he is seeing more than I am...I use cadavers, he has living subjects.

Kevin

 

Hi Kevin,
Can you anatomically describe the exact location of these intercuneiform ligaments? The Color Atlas of Foot and Ankle Anatomy (McMinn, Hutchings, and Logan) indicates branches of the tibialis posterior that insert onto the plantar surface of all three cuneiforms, in addition to the bases of the 2nd, 3rd, and 4th metatarsals. In referring to ligaments that run across the plantar surface of the cuneiforms, is it possible that you are actually dissecting these branches of the posterior tibial tendon? If not, then I would assume that the ligaments must be superior to these tendon branches. What is the diameter of the ligaments and where do they attach?

Thanks,
Jeff Root
jroot@root-lab.com

 

If it is possible, a picture would be welcome also.

Thanks,

 

If you guys can tell me how to get a picture on, I will. What I did was take a dremel tool and remove the dorsal and plantar superficial ligaments of the tarsal bones....they wouldn't fall appart!! O got my maginfying glasses and tried to pull them apart until I got a look at what was inside. not only are there ligamenting BETWEEN the cuneiforms, but the bands of the ligaments go n different dierection. If any of you try this, do your best to tear them apart and letme know how you doi...I can't do it. The multiple angles of fiber are only needed if the joint is expected to recieve tension at different angles, which bring me back to what I have been saying for the last two years about Uga the cave man and how his foot would have had to have worked on uneven surfaces. Further, in geologoc time, we might as well be Uga.....everything that makes us "modern" was created by the top 5% of the people since the ind ustrial revolution. Farming and hunter gathering was with us unto the late 1800s.

By the way, Jeff, good to hear from you, and Javier, if you know how to get a pictur up, I wil do it.

CHeers,
Kevin M

 

Jeff, I don't think I answered one of you questions well...I removed EVERYTHING from a set (several sets, actually) of tarsal, leaving only the dorsal and plantar ligaments...they were completelyremoved from the rest f the foot. Then I took the dremal tool and removed the dorsal and plantar ligaments to reveal the interior. That should be better.

Kev

 

oh...one last thing..the ligments between lat cun and middle are strong, the entire 1st ray side is strong, the weakeds on is between the medial and midde cun. It is wide but narrow.

Kev

 

Hello Kevin,

Just playing devil's advocate role. How could you know that these ligaments have some significant function during human locomotion or foot performance?

Regards,

 

Hey Javier!!

Long time, no talk.......

This question is simple enough. If you load the lat column first, the ligaments act like a linkage that locks the entire midfoot. If you load it from the first ray, the 1st ray stays locked, but gives way in the mid tarsal area....usually at the midal cuneiform, which is why diabetics like to get 3rd ray ulcers andinspite of the fact tha there is a nerve between every met, morton's neuroma usually occurs between 3 and 4. I could go on....but I have been admonished about giving away too much before it is all published, but there are so many bright people here, every response makes me think more. Good to hear from you...don't make it so long next time.

Kevin M

 

Kevin,

I came across a very interesting foot skeleton to add to my collection. The individual obviously functioned in a grossly pronated manner. The talus is adducted on the calcaneus and there is a complete atrophy of the anterior facet of the calcaneus since the head of the talus no longer articulated with the anterior facet of the calcaneus. Although the navicular is adducted as well, it is relatively abducted when compared to the longitudinal axis of the talus. This general adduction and inversion of the navicular results in splaying of the cuneiforms and a loss of medial arch height. In order to resist these types of splaying forces at the cuneiforms, I would think it would take a fairly substantial ligament connecting the cuneiforms. That’s why I was wondering about the anatomical description and location of the ligaments you previously described. While any tissue the crosses the intercuneiform joints in a transverse direction might be capable of generating some tensile forces, what type of structure is needed to resist STJ pronation forces that act to splay the cuneiforms?

One other very interesting feature of this foot skeleton is a huge anterior projection of bone (shelf) from the calcaneus that extends over the proximal, dorsal aspect of the cuboid at the calcaneocuboid joint. This foot did actually have an osseous locking mechanism at the midtarsal joint (calcaneocuboid portion) to stop pronation at the midtarsal joint. The fact that form follows function is very evident in this specimen.

Cheers,
Jeff Root
www.root-lab.com

 

Hello Jeff,

Good to hear from you. Can you get access to a cadaver? If so, take a dremel too with an oval grinder and take of the top ligaments of the tarsal joints. If you can separate them a bit, you can see the intercuneiform ligaments inside. Now the interesting part....if the initial force comes from the lateral column as it is supposed to, the ligament s act like a linkage and lock up the midfoot and the medial to the lateral column. On the other hand....like your specimen, the plantar ligaments have failed enoungh that the calcaneus can plantarflex to much, the linkage fails anfd the 1st ray - like Dananberg said - controls the rearfoot. It does EXACTLY what you described on your foot. I did the very same experiment on a cadaver this week and got the same result you described. It seems that the overlapping joint lines of the 1st ray offer it support in doriflexion to drive the talus medial.....producing the illusion of an everted calcaneus and a pronated foot.

The more of you guys who see this stuff the more exited I get...we are on the verge of knocking out foot mechanics, but I fear there is still a ways to go, though not as far as it has been.

By the way, in my collection of dried feet, I have two that are similar to yours. If you have a "good" specimen, set them side by side and look at the entire midfoot. If you look at one bone, it seems fine, but if you look at the entire foot, you can see that the bones themselves have plastically deformed over time....very col.

Cheers,
Kevin M

 

Hi Kevin,

Nice to talk with you again! Your excitement is contagious!

I will wait for your paper for having a complete response.

Keep working,

 

If you want to e-mail me privately....jkmiller37067@yahoo.com