more BIOM101 clarifications

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Why isn't the 'vertical mid-tarsal joint reference axis' termed 'superior-inferior mid-tarsal joint reference axis' in the same fashion as the other two MTJ reference axes are? Pedantic, yes, but better.
Since the forefoot is, "relatively plantarflexed at rest (non-weightbearing)" (Kirby K, not sure when) does that mean the passive plantar components of the forefoot have greater passive tension than the passive dorsal components of the forefoot?

 

To be pedantic, reference axis could refer to a line that represents the position of the bones on one side of a joint to another. For example, to determine if there is a metatarsus adductus you compare the axis of the rearfoot to the reference axis of the metatarsals.
An axis of motion is a line that describes motion that has occurred between two bodies.
If you chose to move the forefoot in abdcution and adduction relative to the talus and calcaneus you would have a vertical axis of motion. If you chose to simultaneously dorsiflex and abduct the forefoot relative to the rearfoot you would create an oblique axis of motion. The motion determines the axis and not vice versa.

Eric

 

Thanks Dr Fuller, I need to think about the first paragraph to comprehend it. so for relative positions one should use the reference axes of the MTJ (Nester and ?, apologies) whereas relative motion use the 'active' axis?
Still not sure why the 'vertical reference axis of the MTJ' shouldn't be termed the superior-inferior reference MTJ axis?, mark

 

Let me take another stab at it. I've heard of people describe a long axis of the tibia. This is a line that can be used to represent the location of the tibia in space. This version of an axis has nothing to motion. This is in distinction from an axis of motion that describes the rotation of two bodies relative to each other.
Nester's vertical axis of motion is one that he happened to measure. Nester's axis of motion was one that was calculated from actual motion of bones relative to one another. The input forces of walking produced that motion at the midtarsal joint. If you used different input forces you would get a different axis of motion. Don't get to attached to any particular axis of motion. They are just temporary figments of our imagination. They just describe motion that happened at one particular instant in time. That motion may or may not be repeated. Especially for the mid tarsal joint.

Eric

 

Thanks again Dr Fuller. No worries now, your latest post clarifies your first post for me. top post, hopefully its included in students (which I still am) education. I'm fine with axes of motion but love your, 'The motion determines the axis and not vice versa'. I was, in the OP, just being pedantic in wishing Nester and ?(apologies to the other author) had termed that axis the 'superior-inferior' so it had similar form? to the other two MTJ reference axes named. Will save most of your 2 posts to my word.doc file "great posts" which is full of yours, Prof Kirby's, Dr Spooner's, Ian Griffin's etc, mark

 

Mark:

The "reference axes of the midtarsal joint" proposed by Nester and Findlow ten years ago (Nester CJ, Findlow AH: Clinical and experimental models of the midtarsal joint. Proposed terms of reference and associated terminology. JAPMA, 96:24-31, 2006) actually is something that Chris Nester and I had discussed for some time before their paper was written. Chris was lecturing in Sacramento in April 2001 and I had him over my house in Sacramento for a few nights so we could chat and show him around my home town some.

Chris and I had quite a few discussions on midtarsal joint (MTJ) axes during his stay with me, now exactly 15 years ago. We had both come to the conclusion that due to the variability of the MTJ axes, widely moving in space during gait due to the relatively non-constrained nature of the MTJ, that it would be impossible to assign the MTJ axis as being in only one spatial location or to one "average" spatial location.

Rather, Chris and I both felt that it would be best to describe the motions of the forefoot relative to the rearfoot using a set of "reference axes" including a medial-lateral, vertical and anterior-posterior axis which allowed a description of the motions and moments of the MTJ across all three cardinal body planes, regardless of the spatial orientation of the MTJ axis at any instant in gait. Chris and Andrew Findlow had their paper published on this subject about five years later. I have written about the subject of MTJ axes quite a bit in my second book in a series of five newsletters from August to December 2001(Kirby KA: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002, pp. 67-78).

The term "vertical MTJ reference axis" was chosen rather than "superior-inferior MTJ reference axis" since it was a shorter, more concise name that was not ambiguous for the reference axis that described motions and moments within the transverse plane. The term "horizontal MTJ reference axis" could not be used since both the anterior-posterior MTJ reference axis and medial-lateral MTJ reference axis lie within the transverse plane. In other words, there are two "horizontal MTJ reference axes", one axis that describes motions and moments within the sagittal plane (i.e. the medial-lateral MTJ reference axis) and one axis that describes motions and moments within the frontal plane (i.e. the anterior-posterior MTJ reference axis). Hope that makes sense.

Finally, as far as the foot at rest, in a non-weightbearing situation, where the forefoot is being plantarflexed by gravity against the rearfoot, the dorsal ligaments of the MTJ and midfoot will be under greater tension force than the plantar ligaments. During weightbearing, however, the plantar ligaments of the MTJ and midfoot, including the plantar fascia, will be under very large tension forces to resist excessive dorsiflexion of the forefoot on the rearfoot.

There is a Longitudinal Arch Load-Sharing System (LALSS) within the human foot which I have previously described in my fourth book (Kirby KA: Foot and Lower Extremity Biomechanics IV: Precision Intricast Newsletters, 2009-2013. Precision Intricast, Inc., Payson, AZ, 2014, pp. 31-34.). This LALSS model details how the plantar ligaments, plantar intrinsic muscles and plantar fascia work together to share the plantar tension force loads of the longitudinal arch which are required to maintain longitudinal arch integrity (i.e. prevent excessive longitudinal arch flattening and elongation) during weightbearing activities. This is very important to understand how plantar fasciotomy surgeries and plantar fascial ruptures affect the plantar ligaments and plantar intrinsic muscles during weightbearing activities. I have just sent in an article to be published in the July 2016 issue of Podiatry Today magazine on the Ten Biomechanical Functions of the Plantar Fascia which describes the LALSS (see illustration below).

Hope this helps.:drinks

 

Thanks Prof Kirby, I am currently working my way through, "Kirby KA: Foot and Lower Extremity Biomechanics IV: Precision Intricast Newsletters, 2009-2013. Precision Intricast, Inc...... ", top read, thought I should summarise it in a word.doc file but my word.doc file is as 'big' as the book, haven't been able to delete anything, and thanks for the reason behind, 'vertical MTJ reference axis', all the best, mark