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There is obviously good theory and supportive evidence that plantar-flexing the 1st ray is the pathway to biomechanical utopia. The 1st MPJ suddenly 'functions'...windlass mechanism kicks in...high-gear axis push off is more likely etc...


Then you look at the typical patient standing on the typical orthotic device. What you invariably see is no contact at all (orthotic/plantar surface interface) distal to the navicular on the medial side.

Despite the solid theory, something is wrong here IMO. Why bother extending the device beyond the navicular on the medial side anyway? Might as well be thin air, if there is no contact between the device and the plantar surface. Devices don't contour like they used to.

Do GRFs act entirely on the plantar met head, as weight distribution moves past the distal navicular and final medial contact point? If that is the case, then aren't these fashionable devices having the opposite effect?


Time for someone with real (bio)physics knowledge to step in.

I'm not sure what you really want in a reply to this post? I wont' disagree with you that if you have patients stand on their orthotics with both feet they often will supinate away from the medial column.

Depending on the construction of the orthosis, when you test them with an in-shoe system, you will see a similar pattern. Even if you add a 1st ray cutout, sometimes you will still see little increase of the pressure sub 1st ray.
But, if you fill in that cutout with ppt or poron you will tend to see an increase in teh pressure sub 1st ray, especially during mid midstance to early active propulsion.

Evaluating a patient in static stance standing on one or both orthotic devices will never tell you enough about their function. Have them attempt to roll over teh device and at least then you may see that they are still pronating thru the device at the medial column. You may see that you need to add varus posting to your device at the heel to help eliminate this stoppage of motion, you might even need medial expansion or a phlange addition.

There is much to be learned from evaluating our devices wth some active motion on the orthotic devices. Even more so from use of an in-shoe system.
not sure if this answered any of your questions though.
Sincerelhy;
Bruce Williams, DPM

Related threads:
Where Should the First Ray be When Casting for Orthoses?
Foot pronation and 1st MPJ motion
Bojsen-Mollor high gear/low gear
Is forefoot varus posting an anachronism?

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Ron, I have been having similar thoughts to you and have been testing a new device which only extends to the medial cuneiform on medial side. I have called this the "J type" for obvious reasons. Hope to be able to spill more beans soon.

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Simon;
have you tested this device with any backfill of ppt or poron or the like? I think you will see a difference when utilizing a large cutout like your J-type. It does make a difference with and without, but in general I like the effect w/ the backfill.
Good luck to you.
Sincerely
Bruce Williams

Some of my first ray cuts out extend back as far at the cuneiform. ...and don't forget how narrow Mert Root originally made his orthotics.

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Department of Podiatry
La Trobe University
Melbourne, Australia
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Great minds.........................?

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There may be supportive evidence that plantarflexing the first metatarsal when casting has better clinical outcomes than not plantar flexing, but this does not necessarily make the theory good. There may be many explanations as to why a certain technique works. I would look beyond the shape of the foot when casted to explain why the theory works. What exactly is the theory? Is the theory that plantar flexing the met when casting causes the met to plantar flex when the foot is standing on the orthosis? How does that work? Is the theory that plantar flexing the first ray reduces the amount of forefoot varus/ increases the amount of forefoot valgus? Is the theory Plantarflexing the first ray increases the height of the medial arch?

How does the piece of plastic under the foot change the forces and moments acting on the foot to improve clinical outcomes?

Regards,

Eric

I should also add that I do not like using first ray cut outs. I try to avoid them by using different strategies in the casting etc, but following some tips by Bruce and doing some testing at orthoses issue I am finding that I end up using them in 10-20% of orthotics.

I never used to like using them as they never seem to work. But again following Bruces lead, I finally worked out why and now progressivly grind them back further and further until the desired function is achieved .... and sometimes that means going all the way back to the cuneiform.

__________________
Craig Payne
Department of Podiatry
La Trobe University
Melbourne, Australia
http://www.latrobe.edu.au/podiatry
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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
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Ron, Bruce, Craig, Simon, Eric and Colleagues:

I don't agree that plantarflexing the first ray is always beneficial or desirable during negative casting for custom foot orthoses. In fact, in some patients, I dorsiflex the first ray. Dorsiflexion of the first ray produces much better results than plantarflexing the first ray in selected patients. Therefore, the statement:"There is obviously good theory and supportive evidence that plantar-flexing the 1st ray is the pathway to biomechanical utopia", is definitely not something that I would agree with.

I first started plantarflexing the first ray for negative casting back during my CCPM Biomechanics Fellowship in 1984-85 and is the same technique I previously used for "reducing forefoot supinatus" before negative casting . The technique I developed is illustrated in a photo that was created for the chapter I did along with Don Green 15+ years ago (Kirby KA, Green DR: Evaluation and Nonoperative Management of Pes Valgus, pp. 295-327, in DeValentine, S.(ed), Foot and Ankle Disorders in Children. Churchill-Livingstone, New York, 1992). Paul Scherer, DPM, and Jack Morris, DPM, who both came back to the CCPM Biomechanics Department during that time (84-85) would perform a similar technique by dorsiflexing the hallux. I preferred pushing dorsally down on the base of the first ray to accomplish basically the same negative casting variation. I believe that Larry Huppin, DPM, who was one of my students and did the Fellowship about four years after me, widely promotes first ray plantarflexion for negative casting by dorsiflexing the hallux.

I would agree, that if the first ray is plantarflexed during casting and the patient stands on the resultant orthosis,the tendency will be for the foot to not be contacting the orthosis plate firmly, if at all, along the distal first metatarsal shaft. However, this same observation may also commonly be made in those patients who have been casted without the first ray being plantarflexed if the patient's foot has decreased medial column dorsiflexion stiffness (commonly seen in posterior tibial dysfunction). In this scenario, the medial column excessively dorsiflexes while weightbearing so that the more proximal arch structures bear more of the orthosis reaction force (ORF) than the distal arch structures.

The question of whether this type of orthosis casting modification (i.e. plantarflexing the first ray) is desirable or not comes down to one simple point: what is the goal of the foot orthosis?? Is the goal of the foot orthosis to increase proximal medial arch ORF and decrease distal medial arch ORF? If it is, then it can be a useful negative casting modification. In fact, it is the same modification that I have used for the past 22 years in treating many children with flexible pes valgus deformity and is the same modification that I described in the above chapter on treating children's flatfoot deformity with foot orthoses.

However, if the goal of the foot orthosis to reduce proximal medial arch ORF, so that STJ supination moments from the orthosis are reduced, then this modification would be contraindicated. For example, plantarflexing the first ray during negative casting would be contraindicated in patients that have laterally deviated STJ axes that have STJ supination moment-related symptoms such as chronic peroneal tendinitis/tendinopathy, chronic lateral ankle instability, sub 5th metatarsal head/Tailor's bunion symptoms, or lateral dorsal midfoot interosseous compression syndrome. Certainly, patients with these painful pathologies of the foot/ankle would not think that an orthosis made with the first ray plantarflexed was a "pathway to biomechanical utopia".

One must remember that negative casting is only one link in the chain of events that is necessary to producing an optimally-functioning custom foot orthosis. How that orthosis is prescribed, what materials were used in orthosis construction and what shoes the orthosis are worn in all greatly affect orthosis function. A good negative casting modification, no matter how brilliant it is in theory, if used with the wrong orthosis prescription variables, used with wrong orthosis materials or used within poor shoes, will result in a poorly-functioning set of foot orthoses.

First ray cutouts are not something I have used or have felt the need to use in my patient's orthoses. Mert Root's orthoses were made to the first metatarsal bisection which is more wide than a true first ray cutout. Rich Blake's orthoses were always made as wide as the shoe allowed. I agree more with Rich Blake's ideas in this regard (i.e. fill the shoe with as wide an orthosis as possible). First ray cutouts will reduce the ability of the orthosis to resist eversion moments due to the decreased medial width of the anterior edge of the orthosis. However, certainly other very accomplished podiatrists have used these modifications with seemingly good results. Therefore, it is obvious that much further research will be required to know whether these modifications are the best modifications for the patient, or whether the same orthosis effect can be accomplished with a simpler or different orthosis method.

And as far as "high-gear propulsion" is concerned, I'll be so happy when it is widely understood and accepted by the podiatric profession that this concept of "high gear-low gear propulsion" is a gross over-simplification of a very complex process by which the individual chooses which part of their plantar metatarsal heads and plantar digits should be receiving the maximum amount of GRF during propulsion. As far as I'm concerned, this "high gear-low gear" concept should only be taught as a novel historical idea that has little to do with the biomechanical function of the human foot and has little supporting evidence of its biomechanical importance. A high-gear propulsion foot is likely an abnormal foot that has undergone excessive late midstance pronation or that has an excessively abducted gait pattern.

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Sincerely,

Kevin

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Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

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Great thread.

Just a thought. Atlas wrote

and Kevin said:-

Both of these observations are made in static WB (presumably). I Would think that in cases along the lines of functional HL etc the problems would become most relevant after mid stance when the movement of the body COM forces the hallux into dorsiflexion (or not). Do we know if the met shaft is contacting the Orthotic at this point? I tend (with no evidence whatsoever) to think that static WB is not representative of how the foot behaves on the orthotic during gait and would even question whether static WB and dynamic mid stance are comparable. Anyone got evidence either way?

Having said that i would agree with Kevin that Planterflexing the 1st ray is not always the path to joy and have had good results with 1st met shaft pads with some patients. Ist ray cutouts are a somewhat overused modification IMHO.

I've not tried using backfill before. Thanks Bruce, might try that.

Respectfull

Robert

Can you extrapolate on this please Kevin? I think this is what I might be on about...

Robert & Kevin.

The biomechanical utopia statement referred to the profession's current attitude generally; not my personal view in every clinical situation.

Just one hour ago, I advised a patient to temporarily abandon their devices in favour of a forefoot varus wedge.

Anyone who thinks that a forefoot varus wedge is not an anachronism, does not think that plantar-flexing the 1st ray is 'biomechanical utopia'.

Easy chief, i was'nt getting at you. I think we understand where you are coming from. Sometimes you have to state a view before challenging it. :)

I should have said "i agree with Kevin and Atlas"

Nothing wrong with FFvarus wedges either IMO

Robert

One way of performing a more realistic test of how the foot and orthosis function together in dynamic circumstances is to perform a test I wrote about nearly 10 years ago, the orthosis deformation test (Kirby KA: "Orthosis Deformation Test. December 1997 Precision Intricast Newsletter. In Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002, pp. 157-158). The orthosis deformation test is performed by placing the orthosis on the ground, having the patient place their foot on top of the orthosis and then having the patient simulate a step over it while the examiner views the mechanical interactions between the foot and orthosis from either medial or lateral to the foot. The patient must be shown how to do this typically but it is a very interesting test that helps one much better appreciate the changes in orthosis shape that occur as the loading forces shift more to the forefoot.

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Sincerely,

Kevin

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Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

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Ron:

As the metatarsal heads and digits are progressively loaded more by GRF in the latter stages of midstance phase, the resultant increase in medial forefoot dorsiflexion moment will tend to cause the medial forefoot to dorsiflex which will, in turn, tend to flatten the shape of the medial longitudinal arch (MLA). As the MLA flattens, there will be an increase in orthosis reaction force (ORF) in the more proximal medial arch and a decrease in the ORF in the distal medial arch. These dynamic shifts in MLA ORF that occur will be dependent on numerous factors such as the medial forefoot dorsiflexion stiffness, muscle function and orthosis design parameters. In shoe pressure measurement systems, such as the F-scan, are ideal for measuring these dynamic changes in ORF.

I would tend to agree that first ray cutouts are probably overutilized by some podiatrists. I have never used one in the 10,000+ pairs of orthoses I have made for my patients and haven't seen the need for it. In other words, if the patient has irritation in the medial distal arch, then simply modify the orthosis in this area [this irritation most commonly occurs at the distal medial slip of the central component of the plantar aponeurosis]. Removing the medial aspect of the anterior edge of the orthosis will significantly prevent the orthosis from being able to resist late midstance pronation during gait. I would need to see evidence that shows that first ray cutouts are biomechanically desirable in order for me to alter my otherwise very successful foot orthosis protocols.

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Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

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I have a pair of orthoses that don't touch my arch when standing on them. When I ran on them I would get a bright red impression from the edge of the orthosis on the bottom of the foot. N = 1 proof that orthoses that don't touch the arch in stance can have a significant effect on the foot in gait or running.

Along those lines this makes me think about the narrowing of orthoses to "allow" the first ray to plantar flex. Narrow orthoses, especially those with a high arch run a much greater risk of irritation from the medial edge of the orthoses when the foot "hangs over" the edge of the orthosis. You may see increased supination with first ray cut out from pain avoidance. If you see increased supination with a first ray cut out and you don't see an impression in the foot from the edge of the orthosis then I would bet the cause of the supination is the posterior tibial muscle and not increased medial forefoot weight bearing (from plantar flexion of the first ray?).

In addition to Kevin's points I like to dispense ortoses as wide as the shoe because there is less chance of slippage of the orthosis. A narrow device will often migrate to the medial side of the shoe. A narrow device will also tend to dig a deeper hole in the sock liner of the shoe as well.

It reminds me of two things that were taught by Root and Weed. You need a medial expansion on the orthosis to prevent edge irritation and you should always check the impression of the anterior edge of the orthosis in the shoe. By examining the impression in the shoe you can get an idea if the device has shifted medially. Anyone out there doing first ray cut outs have any numbers on how often there is medial shift of the orthosis in the shoe.

Cheers,

Eric Fuller

Eric:

One thing I clearly remember about my rotation at Kaiser Vallejo during my Biomechanics Fellowship and acting as "head biomechanics clinician" once a week is the number of children and adults that had narrow orthoses that were made by previous fellows. These orthoses were often pushed all the way medially on the shoe insole so that there was sometimes a 1 cm gap between the lateral edge of the orthosis and the lateral edge of the shoe insole. This effectively made a lower arched orthosis for the patient since it had migrated so far medially inside their shoe. I think this experience significantly influenced my decision to make wider orthoses and avoid "first ray cutouts" since I started private practice over two decades ago.

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

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**************************************************

You can avoid orthosis migration just adding a pair of pieces of velcro self adhesives.

Regards,

Atlas

I was going to ask a very similar question ie "why is it that 1st ray c/o work so well almost every time"?

I use a CAD-CAM system and lower the 1st ray almost every time.
The Amfit system takes a w/b scan so if the medial column is off the ground in stance or semi w/b stance then there is an automatic infill of the gap. I often/always reduce this by 3-5mm by lowering the first ray from the level of the 1st cuneiform. This in effect is a 2-5 varus post with 1st ray c/o.
If I have a valgus foot I usually lower the 1st ray more and often add to the valgus post or add a reverse mortons ext.


This is my opinion on the kinematics/kinetics of this design. (Dananberg saggital plane theory withstanding of course)

With the valgus f/foot and a stiff (to GRF) 1st ray the foot tends to experience a supination moment and will often have supination related pathology. Allowing the 1st ray to be lower than 2-5 reduces early midstance supination moments. With this foot it is likely that the STJ axis will remain lateral to the medial column.

With valgus f/foot and compliant 1st ray the medial plantar fascia (PF) experiences greater lengthening/strain. As the 1st ray becomes less compliant to GRF due to the increased stiffening of the PF supination moments increase but the PF and Peroneous longus have little mechanical advantge and cannot plantarflex the 1st ray relative to 2-5. With the 1st ray lowered the PF is not strained early in stance and at the right time can apply a plantarflexing moment with a good mechanical advantage. Even tho in the latter case the plantarflexing muscle force may need to be much less.

With this foot it is likely that in the former case that as the gait progresses to late stance the STJ axis may be medial to the medial column. However with the supinating effect of the latter the STJ axis may be more lateral.

With the supinatus f/foot where the medial column is off the ground or not having much GRF applied to it relative to the lateral f/foot the 1st ray c/o would intuitively be redundant. However this has not been my experience (providing the 1st ray is mobile).

If one looks at a skyline view of the met heads then during dorsiflexion of the hallux the 1st mpj will be much lower than 2-5. Even if the neutral position of the 1st ray is not plantarflexed or even if it is dorsiflexed this is usually true.

Therefore I think that as the foot progresses to the propulsive stage it requires, or is more helpful if, the 1st mpj is allowed to be lower than 2-5. Therefore allowing windlass and supination effect and reducing FuncHL.

Where the foot has a supinatus or a normal f/foot - rearfoot alignment but a compliant 1st ray then this may lead to late pronation and FuncHL. Again allowing the 1st ray to plantarflex and 1st MPJ to be lower than 2-5 reults in the PF and muscles having more mechanical advantage at the correct time (earlier) and so the STJ does not experience such large pronating forces in late stance and Func HL is avoided. This will be true regardless of STJ axis position.

I also tend to evaluate the relative passive flexibility / compliance of the lateral column to the medial column and allow more c/o or lateral posting as needed. Although this is usually automaticallyaccomodated in the w/b Amfit scan but not always when a PoP cast is called for. I usually dorsiflex the hallux and plantarflex the 1st ray when PoP casting but then don't ask for a 1st ray c/o. Often I use a reverse Mortons Ext in this case.

Generally the only time I have found that 1st ray lowering may not be useful is when it is elevated and fixed or the MLA is plantargrade and fixed during all of stance phase.

Just my thought and experience, Does it make sense?

All the best dave smith

Javier,

Do you keep a roll of velcro in your reception area? What do patients do when they buy new shoes? You can also glue a piece of cork to the underside of the device. The cork extends to the medial inside of the shoe and the shoe prevents the orthosis from sliding medially. The "buttress" was taught at CCPM in the mid 1980's. You don't need it if you make your orthoses wider.

Cheers,

Eric

I too make an orthosis pretty much as wide as I can get in the shoe. I can't see the point of working out all the prescription variables to then leave it to chance as to where it sits in the shoe.

When Root determined it best to make a narrow orthosis, was his thinking literally to allow the 1st ray to hang off the medial side of the orthosis to promote the windlass mechanism?

Thanks to Kevin, Dave etc for the very helpful tips and discussion in general.

If I recall correctly with what I heard was that he noted in his clinical practice that a number of patients developed back pain with a wide orthoses due to it inducing a functional hallux limitus, so he made them narrower to facilitate that first ray function .... so indirectly it was aimed at the windlass, but that was its effect.

__________________
Craig Payne
Department of Podiatry
La Trobe University
Melbourne, Australia
http://www.latrobe.edu.au/podiatry
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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
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Yes, we keep it. It is a cheap and quick system for solving many problems related to foot orthotics fitting.

Velcro self adhesives are easily found in many places, or they ask us for free.

It is better the velcro solution. Sometimes, patients (mainly females) do not accept a wider device or modifications such as first ray cut outs are needed; thus we have to give them a solution for wearing their orthoses. In my opinion, a foot orthotic at the bottom of a drawer will not help them. There are many materials and designs, we can offer a widely range of options for solving a problem or problems.

Regards,

The vast majority of podiatrists that make orthoses more narrow than the shoe do not understand that by making their orthoses more narrow or with "first ray cutouts" that they will be causing their patients orthoses to shift medially in the shoe during extended weightbearing activities which will, in turn, cause a decrease in effective medial arch height of the orthosis for the patient. As far as I can tell in this regard, podiatric ignorance is podiatric bliss.

After the clinician has gone to all the trouble to properly evaluate a patient, properly cast them for orthoses, and spend their valuable time deciding on the proper orthosis prescription variables for a patient, to have them then, for some unknown reason, assume that a narrow orthosis will somehow stay pushed up along the lateral border of the patient's shoe during weightbearing activities makes no sense at all to me.

The prevalence of this medial shifting of narrow orthoses inside shoes and its biomechanical effects is not only poorly understood but is also an extremely important variable that has received minimal attention in podiatry and has attracted absolutely no research effort at all. The only place that this effect has ever been mentioned within the medical literature, to my knowledge, was in the chapter I did in Ron Valmassy's book 11 years ago (Kirby KA: "Troubleshooting Functional Foot Orthoses", pp. 327-348, in Valmassy, R.L.(editor), Clinical Biomechanics of the Lower Extremities, Mosby-Year Book, St. Louis, 1996.) In this section I talked about the medial buttress pad that was mentioned by Eric earlier that was used at CCPM extensively in the 1970's and 1980's by Dr. Chris Smith for keeping patients' orthoses properly aligned inside their shoes. Here is an excerpt from the chapter that describes this modification: In all the lectures I heard Mert Root give, he never mentioned that by making orthoses more narrow, medial orthosis migration may be an issue. (Possibly if Jeff Root is following along, he can correct me on this.) Actually, the first time anyone ever pointed out the importance of shoe width and orthosis width was my Biomechanics Fellow, Dr. Richard Blake.

All of you students out there looking for a great research project...here is your chance to publish a meaningful research paper for the podiatric literature [which I have already conveniently titled for you ]: The Prevalance and Biomechanical Effects of Abnormal Medial Orthosis Displacement Inside Shoes.

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

Dave, Kevin, Craig and all;

I must say that you did a nice job in explanation David. Lost me a couple of times, but I agree with most of what you said. I will suggest that in use of teh AMFIT system, you can build in a trough under the medial column that works well for a 1st ray cutout. In my practice we backfill this trough so that it functions as a very nice kinetic wedge. Also, we never have medial migration problems because the device is as wide as teh shoe all the time.

I must admit that I had very few if any problems w/ medial migration of my orthotic devices with 1st ray cutouts. Not sure what the fuss is about, maybe if you don't use a topcover to the sulcus or full length its a problem?

Also, you may want to take into effect that you don't really have to dorsiflex teh 1st ray to get a maximally dorsiflexed 1st ray position in your casting technique. If you instead maximally plantarflex the lateral column, the medial column in >90% of instances will automatically become maximally plantarflexed during teh casting technique.

Finally, Kevin, while I very much appreciate your suggestions on not plantarflexing the 1st ray in patients witha laterall deviated STJ axis, I think that really is not entirely true. I think it is much more important to pronate the STJ during casting for these patient than to whether the 1st ray is plantarflexed or not. Plantarflexing the 1st ray during casting will not force the FF to supinate or remain supinated in any case that I have ever seen. You know all to well that if the medial column is too compliant this will not be a problem, and that if it has minimal compliance, that you have to pronate teh foot adn or laterall post the device potentially at the RF and FF to decrease teh supinatory moment. I see very little need to attempt to alter the FF position in this way by attempting to interfere with 1st mpj function.
As David said in a slightly round about way, if you get the metaheads in the same plane inmost instances, you'll have ok function.

Bruce

Bruce:

I was referring to orthoses without forefoot extensions in my description of narrow orthoses that migrate medially inside shoes. Of course, sulcus length topcovers or full length topcovers on orthoses will help prevent medial migration of the orthosis when the orthosis plate is made more narrow.

Increased medial arch height in the orthosis (e.g. caused by plantarflexing the first ray) is not necessary and can even cause problems in patients with symptoms due to increased magnitudes of STJ supination moments. Pronating the STJ during non-weightbearing negative casting will increase the everted forefoot to rearfoot relationship of the foot and does not always result in decreased medial arch height, in my experience. In patients with supination related symptoms, I use lateral heel skives, dorsiflex the first ray in casting, use extra medial expansion plaster thickness, add lateral arch fillers to the plantar orthosis, balance the cast everted and use forefoot valgus forefoot extensions.

__________________
Sincerely,

Kevin

**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
**************************************************

Now to go off on another tangent with this... A rigid functional orthotic has a very usefull charcteristic in that it is RIGID- and therefore the load is distributed around the shell.
Perhaps best to use an example to illustrate -
An individual is markedly pronated has medially devited STJ axis etc. You use an orthosis to apply a force medially to the STJ axis via a medial heel skive or by an inverted posting. The orthosis applies a force on the foot, but also applies a force to the shoe underneath... With a flexible device, this initial force will be underneath the heel- but with a rigid device a sigificant amount will also be applied to the plantar anterior edge where it is also contacting the shoe (assuming the device is balanced). This effectively increases the force that can be applied, and complements the effect of an extrinsic heel post. A flexible material does not allow this.
The connection to this discussion is that by creating a narrower device, you are decreasing the amount of force you can apply with the orthosis. The wider the anterior edge of a rigid device, the greater the force that can be applied. It is for this reason that if I want to make a first ray cut out, I will always try and do it with plaster expansion so that when the device is pressed it can be still made to full width. This helps prevent the medial migration of the orthosis also. I always make my device wide, and then narrow it to the ideal width while issuing it.
Have I made any sense??

__________________
Craig Tanner
Podiatrist
ASPETAR-
Qatar Orthopaedic and Sports Medicine Hospital
Doha
QATAR
http://www.aspetar.com/

Craig:

I basically understand your ideas, but a few points are in order.

First of all, both a more rigid and a more flexible orthosis will apply the same amount of force on the plantar foot. The big difference is that the more flexible device will deform more under a given loading force so that the total force is still the same between the two types of orthoses but the distribution of the orthosis reaction force (ORF) between the two types of orthoses will be different. For example, the more flexible orthosis may have more ORF in the plantar heel and less ORF in the medial longitidunal arch (LMA) while a more rigid orthosis may have less ORF in the plantar heel and more ORF in the MLA due to their differences in deformation under load. They both exert the same loading force on the plantar foot, it is just distributed differently.

Secondly, while I agree that a wider anterior orthosis edge will increase the mechanical stability of the orthosis within the frontal plane, a more narrow orthosis will still exert the same amount of force between its anterior edge and the shoe as a wider orthosis. The difference is that the wider orthosis will have a greater medial moment arm so that ground reaction force will be able to exert a larger inversion moment on the orthosis when eversion moments are placed on the orthosis by the patient's foot. This results in the wider orthosis having a greater potential to resist orthosis eversion moments than the more narrow orthosis will have, but with both of them still being able to exert the same force along the whole anterior edge.

In the end, we are saying basically the same thing, Craig, but I wanted to clarify the mechanics for this very important topic.

__________________
Sincerely,

Kevin

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Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
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Voice: (916) 925-8111 Fax: (916) 925-8136
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Hi Guys,
Another variable I see as important here, and not discussed much in the literature is length distribution of met shafts and relative tension/rigidity of DTML between met heads, these factors have a large influence on how effectively any given forefoot can get it's met heads to function as a team, with each player fulfilling it's role....these factors will influence whether the forefoot of a device ought to be flat or contoured anterior to the edge of a rigid device. I think in general our Aus profession does not do this very well...too much actual hands on skill and time required.....labs don't do that stuff all that well here either. I also think recent thinking has stopped many people using medial wedging of full length of foot or just forefoot medial wedging in cases where it is probably a good idea......there are some very influential and vocal people around in this profession.....
Ron as far as the non-contact with device in static position......I don't think it matters all that much.....it's what happens dynamically and symptomatically that counts....but you already know that too....good conversation starter though.
regards Phill