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Given the advances in biomechanics knowledge since the phrase "first ray hypermobility" was first used, we suggest that it is time to reevaluate this commonly used term in regards to its mechanical accuracy. We suggest that "first ray hypermobility" is no longer an acceptable term when used to describe the mechanical characteristics of the first ray. Not only does it lack the precision to describe the complex interactions of dorsiflexion loading forces acting on the first ray compared to the dorsiflexion displacements of the first ray, hypermobility implies that the main problem with the first ray is that it moves too much, which is a misleading and inaccurate way to describe and understand mechanical function of the first ray in the sagittal plane relative to the other metatarsal rays.
To better understand the mechanics of any object, the forces applied to it and the resulting movement or deformation must be quantified. The scientific disciplines of biomechanics and engineering use the term stiffness to describe the ability of a structure to resist changes in shape. Stiffness is defined as the amount of force required to produce a given amount of deformation or the amount of stress within a material required to produce a given amount of strain in that material. In mechanical studies of biological structures (i.e., muscle, tendons, ligaments, cartilage, and bone) stiffness is often described in units of force required to produce a given amount of deformation, generally in Newtons per meter (N/m). Compliance, which is the inverse of stiffness, is defined as the amount of deformation produced by a given amount of force and is generally described in units of meters per Newton (m/N). Therefore, a structure that has high stiffness will have low compliance and vice versa....
Quote:
We believe that by replacing the imprecise clinical term first ray hypermobility with a more precise, scientifically definable term such as decreased first ray dorsiflexion stiffness, clinicians and surgeons will be better able to accurately describe and understand the mechanical characteristics of the foot and better able to understand the experimental findings of biomechanics researchers. And by sharing common and precisely defined scientific terminology to describe foot function, potential for more effective communication between the practitioner and the biomechanics researcher will be established, which will encourage more rapid growth in knowledge regarding the complexities of the mechanical function of the foot and treatments that may be employed to remedy associated pathology.
Here is the text of Kevin's message posted in the thread linked above:
Quote:
It is my firm belief that the term that we propose in the article, decreased first ray dorsiflexion stiffness, will ultimately replace "first ray hypermobility" in the podiatric and foot biomechanics literature. I will be lecturing on this subject at the PFOLA meeting in November in Vancouver that Paul is organizing (by the way, for all of those interested, I'm not again lecturing on "abductory twist" this year).
In order to understand first ray biomechanics, the term describing it must include not only motion (i.e. mobility) but also force. "Hypermobility" only describes motion (i.e. kinematics) not force (i.e. kinetics). "Stiffness" is the standardly used term within the international biomechanics literature for describing the load vs. deformation characteristics of joints. Therefore, the term decreased first ray dorsiflexion stiffness is the most scientifically accurate and unambiguous term that can currently replace the imprecise, ambiguous and innaccurate term "first ray hypermobility".
Actually, the paper just published in Biomechanics Magazine is a condensed version of a series of six Precision Intricast Newsletters that I did on the concept of stiffness and compliance, dorsiflexion stiffness in metatarsals and dorsiflexion stiffness of the first ray. I think that once the significance of the material in my newsletters and our article is digested further by the profession, then it will become clear that the term decreased first ray dorsiflexion stiffness is the only logical choice for a term to describe the load vs deformation characteristics of the first ray. By understanding my reasoning for my suggested change in terminology, it is my hope that this will elevate our level of understanding of first ray biomechanics and allow podiatrists, orthopedists, physical therapists and pedorthists to discuss foot biomechanics with the same scientific accuracy that the biomechanists and engineers do.
In other words, this is one of my goals ....to help build a bridge of accepted and unambigous terminology between clinicians and researchers involved in foot and lower extremity biomechanics.
Thanks for reposting our article. The change from "first ray hypermobility" to "decreased first ray dorsiflexion stiffness" for terminology to describe the mechanical characteristics of the first ray is really a "no-brainer". I haven't heard one good reason why we should keep "hypermobility" as a term, especially given our current level of knowledge of biomechanics for other joints of the body. It is about time that we started "talking the talk" of the biomechanists and engineers, and losing the imprecise clinical terminology from over 70 years ago.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
I could not agree more ... we have been doing some preliminary work on ankle joint stiffness as opposed to ankle joint range of motion .... what seems to be important (and I am sure the same applies to the first ray) is, its the range of motion at different degrees of dorsiflexion force rather than the total range of motion.
The 10 degrees of dorsiflexon considered normal at the ankle joint is a very bogus number...
__________________
Craig Payne
Department of Podiatry
La Trobe University
Melbourne, Australia http://www.latrobe.edu.au/podiatry
__________________________________________________ ___________________________________ God put me on this earth to accomplish a certain number of things - right now I am so far behind, I will never die.
The views expressed above are those of the author and not that of La Trobe University This is where I am, where are you?
I could not agree more ... we have been doing some preliminary work on ankle joint stiffness as opposed to ankle joint range of motion .... what seems to be important (and I am sure the same applies to the first ray) is, its the range of motion at different degrees of dorsiflexion force rather than the total range of motion.
The 10 degrees of dorsiflexon considered normal at the ankle joint is a very bogus number...
I believe that once a logical, mechanically coherent explanation is provided regarding the problems with only measuring "range of motion", it will become very clear to those that have the best understanding of biomechanics of the necessity to start considering first ray and ankle joint stiffness vs. first ray and ankle joint range of motion.
The ankle is certainly a very important joint to start investigating the mechanical effects of dorsiflexion stiffness (instead of "dorsiflexion motion"). Measuring ankle joint dorsiflexion has always seemed problematic to me due to the large differences in motion which result depending on how much ankle joint dorsiflexion moment is applied (either by the dorsiflexors or the examiner's hand). Considering ankle joint dorsiflexion stiffness tells us much more about the mechanics of the ankle joint than simply measuring only ankle joint dorsiflexion.
In the future, plotting a force vs deformation curve for ankle joint dorsiflexion instead of just measuring "ankle joint dorsiflexion" will yield so much more useful scientific information for the study of human gait biomechanics that we will all be able to look back in a few years and wonder why we didn't consider and demand for a change in terminology sooner.
Good job, Craig, on your work in this regard. We are moving forward in our knowledge!
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Effectively what the student (Lisa Edwards) found was that there was no relationship between range of ankle joint motion and what people did or did not use dynamically at a range of different speeds. Some people do not go past 0 degrees when walking, even if they have the range available, others needed 15 degrees.
We also assumed that as people walked faster, that they would need a greater range - some did, some didn't, some just lifted the heel of the ground sooner (even if they had the range available) --- it was all very subject specific.
Thats why we moved on to "stiffness" rather than "range of motion"....
__________________
Craig Payne
Department of Podiatry
La Trobe University
Melbourne, Australia http://www.latrobe.edu.au/podiatry
__________________________________________________ ___________________________________ God put me on this earth to accomplish a certain number of things - right now I am so far behind, I will never die.
The views expressed above are those of the author and not that of La Trobe University This is where I am, where are you?
Last edited by Craig Payne : 23rd July 2005 at 12:51 PM.
I have great respect for the biomechanics experts in our field. But I fail to see how changing the understandable terminology of "hypermobility of the first ray" to "decreased in first ray dorsiflexion stiffness" is at all helpful. Exactly how is this proposed change in terminology going to result in more meaningful research and understanding of biomechanics? The verbiage, "decreased first ray dorsi-flexion stiffness," is awkward at best. It is stated in the negative. It is like saying, "not a left turn," instead of saying "right turn." Part of the knock on podiatric biomechanics is that it is difficult to understand. I think that changing the simple terminology that has been present for years and is accurate enough, to something more arcane, would be a disservice to the profession. Call me old- fashioned, but I know what "hypermobility of the first ray" means. "Decreased first ray dorsi- flexion stiffness" hurts my head just thinking about
It is interesting to note here that Doug Milch, DPM, who is the author of the above posting did the CCPM Biomechanics Fellowship a year before I did the Fellowship.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
I agree that stiffness is a better term than hypermobility. We still have to remember that relative muscle activation will alter the stiffness. There is more than one thing that can contribute a resistance to motion. The ligaments and the muscles will alter the measurement of stiffness.
I agree that stiffness is a better term than hypermobility. We still have to remember that relative muscle activation will alter the stiffness. There is more than one thing that can contribute a resistance to motion. The ligaments and the muscles will alter the measurement of stiffness.
A decrease in first ray dorsiflexion stiffness may be caused by either anatomical or functional factors (Figure 3). Anatomical factors may include increased laxity of the plantar ligaments (i.e., decreased ligamentous tensile stiffness) of the navicular-first cuneiform and/or first metatarsal-cuneiform joints. Surgical transection of the medial fibers of the central component of the plantar aponeurosis will also reduce first ray dorsiflexion stiffness since the plantar aponeurosis (plantar fascia) functions to help prevent dorsiflexion of the first ray.16
Functional factors include a decrease in contractile activity of muscles (e.g., peroneus longus, flexor hallucis longus, abductor hallucis, and flexor hallucis brevis) that may cause a first ray plantarflexion moment. Decreased contractile activity of any of these muscles during the late midstance phase of walking gait, when the dorsiflexion loading forces on the first ray are at their greatest, will tend to decrease the magnitude of the first ray plantar-flexion moment, which will in turn mechanically decrease the dorsiflexion stiffness of the first ray.17 Stokes et al18 developed a model of the first ray-first metatarsophalangeal joint complex that provides considerable insight into the functional factors that likely affect the mechanical resistance and response of the first ray to dorsiflexion loading forces during weight-bearing activities.
One of the first problems we will encounter as we start to understand the mechanics of the first ray more completely, is that we don't necessarily know whether there is increased first ray dorsiflexion stiffness coming from passive factors, such as ligamentous tensile force and joint compression forces, or from active factors, such as muscle contractile force. However, the bottom line is still that if we see that the first ray dorsiflexes less with either the same or increased dorsiflexion loading force, then we know for certain that the first ray dorsiflexion stiffness has increased. In addition, if we see that the first ray dorsiflexes more with either the same or decreased dorsiflexion loading force, then we know that the first ray dorsiflexion stiffness had decreased.
At least getting podiatrists to acknowledge that both dorsiflexion motion and dorsiflexion loading force (and not just dorsiflexion motion or mobility aone) are critical to understanding the mechanics of the first ray relative to the lesser metatarsal rays will be a huge step ahead for the podiatry profession. Overcoming this intellectual hurdle will allow podiatrists to achieve a more complete grasp of the mechanical function of the metatarsal rays as it relates to the function of the foot and lower extremity as a whole.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
These new descriptions are valid from a research based point of view and hopefully herald further treatment modalities, however at this particular moment in time they are only descriptions. In busy practises with limited time/resources and patients demanding 'comfort' first and 'correction' last it is difficult to measure forces and degrees. It is easy to judge at the extremes whether someone demonstrates joint hypermobility ( which is usually throughout the body ) or has a 'limited range of motion' which tends to direct us to functional devices or not. At these extremes I am not sure that a great deal can be achieve in altering the gait in any particular meaningful way. Hyper has always been associated with 'excessive' or as described above 'moves too much'. 'Limited' tends to mean 'restricted' or 'moderate' movement. Where I think this new terminology may be more appropriate is in the middle area where we probably need something to describe the dreaded 'normal' amount of stiffness to work out if it is decreased or increased.
As can also be seen from Lisa Edwards research all the patients varied their ankle joint motion at different stages of gait cycle and at different speeds and there seem to be too many variables terrain/cadence/footwear etc to dtermine accurately not only what the patient is doing with each step but also much more importantly from a practitioners point of view how to prescribe a suitable device. That is for the present but I hope the reseach expands the development of new orthoses and easier ways of measuring.
These new descriptions are valid from a research based point of view and hopefully herald further treatment modalities, however at this particular moment in time they are only descriptions. In busy practises with limited time/resources and patients demanding 'comfort' first and 'correction' last it is difficult to measure forces and degrees. It is easy to judge at the extremes whether someone demonstrates joint hypermobility ( which is usually throughout the body ) or has a 'limited range of motion' which tends to direct us to functional devices or not. At these extremes I am not sure that a great deal can be achieve in altering the gait in any particular meaningful way. Hyper has always been associated with 'excessive' or as described above 'moves too much'. 'Limited' tends to mean 'restricted' or 'moderate' movement. Where I think this new terminology may be more appropriate is in the middle area where we probably need something to describe the dreaded 'normal' amount of stiffness to work out if it is decreased or increased.
As can also be seen from Lisa Edwards research all the patients varied their ankle joint motion at different stages of gait cycle and at different speeds and there seem to be too many variables terrain/cadence/footwear etc to dtermine accurately not only what the patient is doing with each step but also much more importantly from a practitioners point of view how to prescribe a suitable device. That is for the present but I hope the reseach expands the development of new orthoses and easier ways of measuring.
Philip:
True, it is difficult in a busy clinical setting to measure the load vs deformation ("force vs degrees") characteristics of any joint of the foot, including the first ray. That is not the point. The point is that the currently used terminology "hypermobility" does not allow accurate description of the mechanics of the first ray (or any joint for that matter) since it leaves out that very important quantity: force.
"Hypermobility" can not be adequately researched since it is not a quantifiable term. In other words, do we say that the normal first ray has normal mobility and the first ray that requires more force to move it is a "hypomobile first ray"? Why not use a term, such as stiffness, which is already in common use in the international biomechanics literature and that describes the mechanics of the first ray much more precisely and unambiguously.
The importance for the clinician in using the term stiffness of the first ray is that it is intended to make them start thinking in terms of force instead of just position, structure and motion. This is no different than my trying to get podiatry, over the past 20 years, to start talking about moments across the subtalar joint, midtarsal joint or ankle joint, instead of just the position, structure and motion of these joints. If the clinician understands the mechanics of the foot, which always will include consideration of the external and internal forces and moments involved, they will not only better understand the etiology of injury but will also understand how best to make their patient asymptomatic with mechanical therapies.
If, Philip, you can comfortably use the term "moment" in describing the mechanics of the foot, then you should have no problem using the term "stiffness" to describe the load vs deformation characteristics of any joint of the foot and/or lower extremity. If you want to understand more about how the foot and lower extremity work, then I suggest you learn these terms and what they mean. If you want to, however, let your knowledge of the biomechanics of the foot and lower extremity stagnate at its current level for the remainder of your practice career, then, there certainly is no need to learn what either "moment" or "stiffness" means in the many foot biomechanics research articles that currently use these terms.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Sorry for that last comment. In rereading both of our posts again, I can see that you seem to understand the concept of stiffness. My mistake.
However, to reemphasize my point about stiffness, it is a very commonly used term in foot biomechanics research currently. Here is an abstract from the September 2005 issue of the Journal of Biomechanics that uses the term "stiffness" to describe the load vs deformation characteristics of the forefoot at the MPJs during running barefoot versus the stiffness of running shoes. I believe it will be very positive for the podiatric profession, especially in the eyes of other scientifically minded medical professionals and biomechanics researchers, to be the first clinical specialty to discard the term "first ray hypermoblity" and replace it with "decreased first ray dorsiflexion stiffness".
Quote:
A comparison of forefoot stiffness in running and running shoe bending stiffness
J Biomech 2005 Sep;38(9):1886-94 (ISSN: 0021-9290)
Oleson M; Adler D; Goldsmith P
Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive, N.W. Calgary, Alberta, Canada T2N 1N4.
This study characterizes the stiffness of the human forefoot during running. The forefoot stiffness, defined as the ratio of ground reaction moment to angular deflection of the metatarsophalangeal joint, is measured for subjects running barefoot. The joint deflection is obtained from video data, while the ground reaction moment is obtained from force plate and video data. The experiments show that during push-off, the forefoot stiffness rises sharply and then decreases steadily, showing that the forefoot behaves not as a simple spring, but rather as an active mechanism that exhibits a highly time-dependent stiffness. The forefoot stiffness is compared with the bending stiffness of running shoes. For each of four shoes tested, the shoe stiffness is relatively constant and generally much lower than the mean human forefoot stiffness. Since forefoot stiffness and shoe bending stiffness act in parallel (i.e., are additive), the total forefoot stiffness of the shod foot is dominated by that of the human foot.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Yes I have studied many of your papers and enthusiatically taught such other great terminology that you have described..the Kirby skive, finding the STJ axis and many more. I have also digested other difficult papers by many other respected authors for the last 20 years and have 'treated' many hundreds of patients with mostly good results and an appreciation that I have tried to keep up to date in knowledge as well as good practise.
I have also tapped into some recent and past discussions on this arena and held back replying precisely because of this type of professional put down by the very people whose work has inspired me.
I have worked in researching new products (wet lay carbon fibre orthoses 1990) and have one or two inventions currently being used by a number of podiatrists (Easyform system and Contra-orthoses). It is quite difficult practising entirely on you own and earning an honest living and most times one has to be a 'Jack of all trades' and maybe a 'Master of none'.
I have Roots original Biomechanical Examination of the Foot Vol 1 and still feel it draws most of its old ideas together nicely and concisely, even though I agree not relavent to day in all aspects. But is there currently available a book/manual/method that brings all the new ideas together that allows someone to follow a guide based on any of the current new set of principles?
No, so we rely on forums like this to HELP each other and yes to criticize and correct misconceptions.
Sorry for the rant, I think I also had a nerve exposed!
Incidently Ian and I have in the past had many a heated nights debate over a few glasses and will continue to seek the truth and make sure that the 'Kings' are not wearing just their birthday suits.
Incidently Ian and I have in the past had many a heated nights debate over a few glasses and will continue to seek the truth and make sure that the 'Kings' are not wearing just their birthday suits.
Sorry again for my comments, Philip. It has been a tough weekend for me and I regret ever making those comments.
Please accept my apologies.
I'll imagine that you and Ian do have some good discussions. I hope that both of you keep up the good comments on this forum and don't let my "raw nerves" discourage you from further contributions.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Kevin
Nice to speak with you. I too have had a tough weekend and realise you didn't mean anything. Keep up your good research and I look forward to learning from you again from afar. I have always been a bit touchy and my natural instinct has always been to question.
On another note more relevant to podiatry, I am researching ( in my own style) a different approach to casting feet in a semi weight bearing position with some very encouraging results. Hope to post some information soon.
Sincerely
Philip
At sea level, at a temperature of 0 degrees Celcius, one cubic centimetre of air (that is, a space about the size of a sugar cube) will contain 45 billion billion molecules. And they are in every single cubic centimetre you see around you. Think how many centimetres there are in the world outside your window - how many sugar cubes ir would take to fill that view. Then think how many it would take to build a universe.Bill Bryson - A Short History of Nearly Everything
Is it to late to come back from the general developed language of Biomechanics and consider the human joint again using the terms of Applied Mechanical Engineering?
For example turning moments, applied forces and the stiffness of joints considering the friction and viscosity of a joint!
Is the use of traditional understanding of load bearing joint testing not applicable to the measurements of joint movement perhaps without the foot falling off today of course? (Testing to destruction perhaps not a good idea?).
Regards,
Colin.
PS. Excuse my ignorance here but is Biomechanics used in place of Applied Mechanic Engineering? Or is it the bases of Biomechanics, anyway?
My knowledge extends to the text book:- Basic Biomechanics of the Musculoskeletal System by Nordin M. & Frankel V.H. who appear to be applying Mechanic Engineering at that time (1980's.?).
Is there any contact or cooperation with pure engineering university faculties at present or have the two disciplines gone their own way completely?
Bearing in mind Mechanical Engineering was always couched in experimentation, accurate measurement with observation. There was no room for surmise or theorization unless it was firmly centred on these three previously mentioned!
PPS. Am I trying to return to first principles whilst Biomechanics has moved onto another plain completely now with no return or reason for return?
PS. Excuse my ignorance here but is Biomechanics used in place of Applied Mechanic Engineering? Or is it the bases of Biomechanics, anyway?
My knowledge extends to the text book:- Basic Biomechanics of the Musculoskeletal System by Nordin M. & Frankel V.H. who appear to be applying Mechanic Engineering at that time (1980's.?).
Is there any contact or cooperation with pure engineering university faculties at present or have the two disciplines gone their own way completely?
Bearing in mind Mechanical Engineering was always couched in experimentation, accurate measurement with observation. There was no room for surmise or theorization unless it was firmly centred on these three previously mentioned!
PPS. Am I trying to return to first principles whilst Biomechanics has moved onto another plain completely now with no return or reason for return?
These are very good questions. Within the international biomechanics community, some of the best biomechanics minds were originally trained as mechanical engineers. I believe biomechanics is very broad now, encompassing engineering concepts, physics and biological processes. You may want to scan through some of the articles in the Journal of Biomechanics to see what I mean (abstracts are available online for free).
There are many good reference books on biomechanics and I buy all of the ones that look good for my library. If a podiatrist had to buy just one book to get "up to speed" on biomechanics terminology and fundamentals, then I would get the textbook by Ozkaya and Nordin (Ozkaya, Nihat and Margareta Nordin: Fundamentals of Biomechanics: Equilibrium, Motion and Deformation. 2nd Edition. Springer Science & Business Media, Inc, New York, 1999). It gives both basic and advanced information and this book, and its earlier editions, have been very helpful to me over the last decade of learning.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Thank you for your most enlightening reply! I will be following up your suggestions. I hope my questions have not disrupted the flow of a most interesting Thread here?
This is all very interesting!I can see why we would want to update our terminology,however,I myself will need some time to adapt to it.Also,with the case of a hypermobile 1st ray,patients may know that terminology as well.Another thing lost in this debate: A plantarflexed 1st MT head and a hallux elevatus/rigidus/limitus is also extremely relevant here.I think that most of the pathology comed from the plantarflexed 1st MT head as well as the hypermobile 1st ray.I guess my main point is:let us fix the pathology first,then as Dr.kirby so eloquently put it,we can change the nomenclature to reflect modern knowledge.Just my opinion.
This is all very interesting!I can see why we would want to update our terminology,however,I myself will need some time to adapt to it.Also,with the case of a hypermobile 1st ray,patients may know that terminology as well.Another thing lost in this debate: A plantarflexed 1st MT head and a hallux elevatus/rigidus/limitus is also extremely relevant here.I think that most of the pathology comed from the plantarflexed 1st MT head as well as the hypermobile 1st ray.I guess my main point is:let us fix the pathology first,then as Dr.kirby so eloquently put it,we can change the nomenclature to reflect modern knowledge.Just my opinion.
John,
I don't think patients will have a problem with this concept at all, as long as you explain it in easy-to-understand terms. In fact, I think that by explaining that their first ray is too flexible, or is not able to support as much load as their adjacent 2nd ray, then they should easily be able to understand the concept of decreased first ray dorsiflexion stiffness. One may say to the patient that their second ray is stiffer than their first ray and so that it can support more load than the first ray can and that is why their second metatarsal has a painful callous or a plantar plate injury. Do you think that above concepts would be difficult for a patient to understand? I don't.
I do agree with you in regards to first metatarsal head vs lesser metatarsal head position in the nonweightbearing (NWB) position of the forefoot. This is another parameter, in addition to metatarsal ray stiffness that could cause pathology.
For example, if the first ray and second ray have identical load vs. deformation curves, but in the NWB position the first metatarsal head is 5 mm dorsiflexed relative to the second metatarsal head (possibly from a bunion surgery), then this dorsiflexed position of the first ray relative to the second ray may also be a cause plantar 2nd metatarsal head symptoms. This is because the second ray will need to be dorsiflexed 5 mm relative to the 1st ray before these metatarsal rays are on a common plane and this will put the 2nd ray at a steeper portion of the load vs deformation curve (more dorsiflexion stiffness) where more loading force on the 2nd metatarsal head is exerted.
On the other hand, if the first ray and second ray have identical load vs deformation curves, but in the NWB position the 1st metatarsal head is 5 mm plantarflexed relative to the second metatarsal head (possibly from a "plantarflexed first ray deformity"), then this plantarflexed position of the first ray relative to the second ray may a cause of plantar 1st metatarsal head symptoms (e.g. sesamoiditis). This is because the 1st ray will need to be dorsiflexed 5 mm relative to the 2nd ray before these metatarsal rays are on a common plane and this will put the 1st ray at a steeper portion of the load vs deformation curve (more dorsiflexion stiffness) where more loading force on the 1st metatarsal head is exerted.
Understanding metatarsal ray function in this fashion, with each metatarsal ray having a spring like function where the load exponentially increases with each mm of dorsiflexion motion of the metatarsal ray, is certainly made very clear once you have read the research and Master's thesis by Fauth (Fauth AR, Hamel AJ, Sharkey NA: In vitro measurements of first and second tarsometatarsal joint stiffness. J. Applied Biomechanics, 20 (1): 14-24, 2004) and the research on forefoot stiffness from Ker at al (Ker RF, Bennett MB, Bibby SR, Kester RC, Alexander RMcN: The spring in the arch of the human foot. Nature, 325: 147-149, 1987). Each metatarsal ray acts independently and dependently of each other metatarsal ray in regards to their load vs deformation characteristics and in regards to dorsiflexion stiffness of the forefoot as a whole. I believe that understanding the metatarsal rays using these parameters, rather than just looking at NWB position and structure, will help explain many clinical phenomena that are otherwise confusing and unclear.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
For example, if the first ray and second ray have identical load vs. deformation curves, but in the NWB position the first metatarsal head is 5 mm dorsiflexed relative to the second metatarsal head (possibly from a bunion surgery), then this dorsiflexed position of the first ray relative to the second ray may also be a cause plantar 2nd metatarsal head symptoms. This is because the second ray will need to be dorsiflexed 5 mm relative to the 1st ray before these metatarsal rays are on a common plane and this will put the 2nd ray at a steeper portion of the load vs deformation curve (more dorsiflexion stiffness) where more loading force on the 2nd metatarsal head is exerted.
When trying to treat these misalignments of metatarsal heads (in NWB STJ neutral) should the treatment involve
1. Plantarflexing the 1st met to bring it into allignment.
2. Dorsiflexing the lesser metatarsals.
3. Filling in the area under the 1st to 'bear' some weight.
4. Varus posting the forefoot.
5. WB or semi WB casting to 're-allign' the mets.
As mentioned in previous threads I have found some very good results casting semi WB in NCSP (or generally slightly pronated) and then extrinsically posting the rearfoot to this position. The plane of the lesser metatarsals is hoizontal and held by the 'in built' forefoot posting and seems to go someway to comfortably address the problem of the level of force being placed on each of the met heads. It certainly effects the build up of callus. It may seem simplistic and I know that it goes against the concept of capturing the rearfoot to forefoot relationship and preventing the compensation but it does appear to work well with many patients.
Precise naming aids dorsiflexion stiffness diagnosis
Seeker of the truths
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