Is forefoot varus posting an anachronism?

Sam,

i can see how valgus posts or similar (rev Mortons, kin wedges 1st ray out etc) they all work around everting the forefoot which is going to facilitate windlass etc...

ff varus posting with 1st out seems like a totally different kettle of fish... you are trying to encourage 1st met function whilst supinating the rest of the forefoot...

i am guessing the goal is to reduce calc eversion, but if you think about it in terms of STJ axis postion there would be many better places to apply such a force depending of how far medially it is deviated.

 

I was aware of the slight conceptual difference between the two, but I wouldn't be surprised if they both behaved very similarly.. there would be only so high you could go with a ff varus posting + first ray cut out before it turned into something resembling a poorly placed met dome, and how high would you need that inclination to go to get the desired effect... what would the desired effect be...? It seems the important part of this modification is the 1st ray cut out.

It's my understanding that FF intrinsic varus posting is used to "balance the rearfoot" in an old fashioned type device. This works under the assumption that the foot should be operating around STN, so i guess you'd be right that the goal is reduced Calc eversion. But now we have been enlightened SALRE and tissue stress principles this appears to be incorrect. Which means your last point is also correct.. But, even with a laterally deviated STJ axis... how much of a significant supinatory moment could you get from a forefoot 2-5 varus wedge...??

Kind regards,

Sam

 

Makes sense to me Sam,

part of my role at the lab i work for is to interpret orthotics prescriptions, and this style of Rx would pop up quite frequently from more than one customer. It always makes me scratch my head and wonder!

 

Sorry, its only in abstract form from a confernece. Its on a long list of publications that I need to get to.

But try this: Do Jacks test. Put felt under first ray to simulate forefoot varus post. Do jacks test again.

 

Hi Craig,

i did have a go myself - not very efffective!! From how I understand biomech a ff varus post (including the 1st ray) should make make the jacks test more difficult. Although it may be argued that it may change COP more laterally! In any case 1st mtpj function is reduced.

However it is a ff valgus post with a cut out to the 1st mtpj that I am querying: HOW will that decrease the amount of force needed to initiate the windlass? Surely the force needed is the same with either orthoses, however the amount of motion that is needed to produce the same windlass effect may be different - such as in a forefoot varus. Surely - force is the result of time over resistance?

Peter

 

Craig -

it's just that you said that you treat plantar fasciitis with forefoot valgus posting (didn't you?)

thanks,

Peter:boxing:

 

Routinely. Its still in conference abstract form, but we showed that in those with plantar fasciitis, that the force to dorsiflex the hallux (ie jack test) is higher. If you elevate the lateral forefoot the force to dorsiflex the hallux goes down ... simple tissue stress stuff.

 

Hi Craig,

thanks very much. Looking forward to it!!!

Peter

 

Well, the left looks MASSish, more likely to immobilize the midtarsal joints than the right and looks like it has less fill. In comparison to the right, it's definitely more aggressive and intuition suggests you're asking us to compare mass posted devices with neutral.

 

The windlass mechanism helps stiffen the first ray in the direction of dorsiflexion of the ray. It does this by creating an internal plantar flexion moment of the first metatarsal. Tension in the windlass will also tend to increase supination moment at the STJ in most feet. (see my paper in JAPMA on the Windlass from 1999 or 2000 for pictures.) So, the windlass prevents both first ray dorsiflexion and STJ pronation.

What you are doing with a forefoot varus wedge is to attempt to supinate the STJ by increasing force on the medial column. (Increased force on medial forefoot and less force on the lateral forefoot will tend to move the center of pressure more medial.) This will simultaneously increase the external dorsiflexion moment on the first ray and decrease the pronation moment on the STJ. The problem is, most of the time, it will increase the dorsiflexion moment on the ray more than it will decrease the pronation moment on the STJ.

With first ray dorsiflexion, the distance between the hallux and the calcaneal attachement of the fascia will increase. This will tend to increase tension in the fascia and other structures attached to the base of the proximal phanlanx. These distal to proximal forces on the phalanx will create a plantar flexion moment on the hallux that will make it more difficult for you, the clinician, to grab that toe and dorsiflex it.


I hope this helps,

Eric

 

The medial anterior edge is much more proximal on the left. Some would call that a first ray cutout. Agree the arch height looks higher on the left. I would give it a more aggressive rather than a much more aggressive.

I have a problem with the term immobilize the MTJ. I don't think a piece of plastic under the foot can immobilize the MTJ. A better term might be resist plantar flexion of the rearfoot, if that is what you mean.

Cheers,

Eric

 

Great discussion, thanks to all, I'm learning a lot from this thread. Just a couple of questions. Firstly Craig, I think I am correct in saying that you stated that those patients with PF require higher forces to establish the windlass. Can you tell me whether you are saying that they have a foot type which is predisposed to PF due to the higher forces required or that while they are symptomatic their foot function changes, resulting in higher forces being required and that this returns to lesser forces when the condition is resolved? Phill, you said that if we can achieve 1st ray plantarflexion then we will resupinate the STJ. Is it conceivable that we only need to achieve 1st Ray plantarflexion with our devices then and forget the rearfoot post?

 

I do not have an opinion as to whether its posting is an anachronism, but I do question the very existence of FFV. We should remember two facts. 1) there is no evidence of any description anywhere that correlates talar head torsion to forefoot-hindfoot relationship, and 2) there is no evidence of any kind anywhere (though much to the contrary) that relates a perpendicular relationship between the plantar surface of the calcaneus to is posterior bisection line. Thus, the basis for aetiology and the basis for its diagnosis are both invalid. Food for thought?

 

The tissue stress approach would say that when structures are under higher stress they are more likely to hurt/ be injured. So, I would expect that the foot with plantar fasciitis to have a difficult to establish windlass both when they are and are not symptomatic.

The windlass mechanism is the interrelationship of several joints. STJ supination and first ray plantar flexion are both involved. It will be easier to plantar flex the first ray when you decrease STJ pronation moment. On the other hand you can have a high pronation moment from the ground with the first ray plantar flexed and the plantar flexion of the met will not cause supination of the STJ. Think of the Coleman Block test with full weight bearing. The lateral pressure will create a high pronation moment, there will be no force under the first met head and the met will plantar flex as the STJ stays pronated.

Eric

 

If temporary relieves the stress to relieve the pain this is good. It depends on the mechanism of injury. Take an inactive individual and make them walk 10 miles. If you cure them with a temporary device they might not take the 10 mile walk again.

I see a lot of patients with plantar fasciitis that comes and goes. I see a lot of them where it comes back less if they wear their orthotics. (My wife is one of those people. She just gets tired of wearing them... Honey, my feet hurt... Were you wearing.....


Eric