Maybe it's time to discuss this again. There seems to be this notion within the profession of late that forefoot varus wedging reduces hallux dorsiflexion and "causes" hallux limitus. I'm not sure where this idea comes from?
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You see we have Kilmartin's bone pin study which showed a 2 degree difference in hallux dorsiflexion with Root orthotics. Like wow, 2 degrees, and the error in your measurement? ...About 2 degrees? But we don't know whether the forefoot was posted varus or valgus. And then studies like:
http://mortonsfoot.com/articles/halluxlimitus.pdf which show that forefoot varus wedging doesn't necessarily reduce peak dorsiflexion at the hallux... in fact, in the majority of subjects, it increased it. Indeed, a higher medial longitudinal arch in the devices reduced hallux dorsiflexion in more subjects than the forefoot varus wedging did. See figure 5, both kinds of devices increased the mean peak hallux dorsiflexion.
Is this some kind of urban myth that is being developed? Am I missing something?
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Varus forefoot extensions, if done in isolation without a foot orthosis, will tend to reduce hallux dorsiflexion, in my clinical experience. Varus forefoot extenions will cause ncreased 1st metatarsal head dorsiflexion moment during late midstance, will cause increased plantar fascial tensile force, increased internal hallux plantarflexion moment and increased tendency for reduced hallux dorsiflexion during propulsion in walking.
I think the variability in response with varus forefoot extensions comes when an orthosis is used along the varus forefoot extension since the orthosis may or may not modify the response seen of the varus forefoot extension, due to the large design variablity seen with foot orthoses. Howevr, I can't think, off the top of my head, of any research to back this up but have seen clinical evidence of this observation many times over the past quarter century. -
Now, we did do a study in which we used forefoot valgus and varus extensions in isolation (at the same time that we did the study on rearfoot posts in isolation that was published in JAPMA) I just can't remember what we found though.:bash:
The bottom line is that I want to know: do foot orthoses with a forefoot varus wedge cause hallux limitus? Do foot orthoses with a forefoot varus wedge reduce peak first MTPJ dorsiflexion? Do foot orthoses with a forefoot varus wedge increase hallux dorsiflexion stiffness? What does the literature tell us?
Is increased hallux dorsiflexion stiffness a negative thing? Is reduced hallux dorsiflexion stiffness a negative thing? Does the hallux have a zone of optimal dorsiflexion stiffness? We have theoretical discussions of how too much stiffness might be detrimental, do we have any that describe how too much compliance might be detrimental? Or do we presume that the more compliance, the better? Flail hallux?
So, if I wanted to study this, I might start with a forefoot varus extension of varying degrees placed under the 1st MTPJ and extended distally and measure hallux dorsiflexion stiffness (as oppose to peak dorsiflexion) in static stance... right MW -
So, in a foot with a more laterally positioned STJ axis, I would expect less stiffening than in a foot with a more medially positioned STJ axis. So, if you do the study assess STJ axis position.
Eric -
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It seems like a large portion of the population develops hallux limitus. It would be interesting to look at what foot characteristics are present in feet that don't develop hallux limitus.
In testing my own medially deviated STJ axis foot, yes a forefoot varus wedge does increase stiffness. And an orthotic with a reverse Morton's extension decreases stiffness.
Too much compliance: I feel that the purpose of toes is to increase area of contact to reduce pressure. The energy studies show that there is energy absorption, rather than production from the MPJ's at toe off. So, they don't add energy to gait. So, a floppy toe will have little force applied by the ground and body weight will have to be supported by the met heads after heel lift. So, it is certainly possible for pathology to develop in the presence of an overly compliant toe.
Eric -
Instinctively, I read this study and found it contrary to what I see clinically. That is to say that, in cases where I think that increased dorsiflexion stiffness of the first metatarso-phalangeal is the cause of the pathology, "improving" or reducing the dorsiflexion stiffness via a reverse mortons extension or similar seems to have a beneficial effect on the pathology.
So, it was with a degree of skepticism that I read the results acheived in this study. Difficult to pick many gaping holes in the study, I thought.
There were a couple of things I thought were worth pointing out
1. The FF POST devices had a forefoot posts that terminated proximal to the 1st met head, not FF varus extensions
2. All subjects had 10 degrees of FF varus. That's FF varus, not supinatus. In such participants, will the lack of 1st ray plantarflexion not significantly affect the results, or are they talking about FF supinatus? -
Like Simon, I also think we must be careful assuming that varus forefoot extensions or varus extrinsic or intrinsic posts on orthoses will always limit hallux dorsiflexion of all feet. We simply don't have the research to back up this idea. However, from what I have seen clinically, a varus forefoot extension has much more "power" in producing reduction in hallux dorsiflexion than does a varus forefoot post, ending at the metatarsal neck. -
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I think there are a few things to consider here. Firstly, I agree with simon that we must get away from sweeping kinematic statements like "reduce hallux dorsiflexion" when what we mean is "increase hallux stiffness". Sometimes I want to increase hallux stiffness and in those cases a FF varus extension is a good thing.
However I also agree with Kevin and Eric that, in general, forefoot varus wedging increases hallux stiffness. Something I've not seen anyone yet state (sorry if I've missed it) is that increasing the dorsiflexion moments and the plantarflexion moments by the same amount won't affect the movement of the hallux but it WILL increase the interarticular compression within the 1st MPJ. And that, in my experience, is rarely a good thing.
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Even early on in the history of Root et al biomechanics, forefoot varus was much more common than forefoot valgus at the California College of Podiatric Medicine. Jack Morris, DPM, when he came back to CCPM to teach biomechanics after having been in private practice for about 15 years, said that when he left CCPM as a student all the feet had forefoot varus and when he got back to CCPM in 1984 to teach all the feet now had forefoot valgus. We both laughed about that one.
In addition, if you ever get a chance to inspect one of the original measuring devices advocated by Root and Weed to measure the forefoot to rearfoot relationship, what do you think you see printed on the device? Not "forefoot to rearfoot measuring device", not "forefoot varus/valgus measuring device" but this.....FOREFOOT VARUS MEASURING DEVICE.
Makes you wonder, doesn't it?! -
True thing.
The more we learn the less we know.
Seriously though, short of X rays, how easy is it to tell if an inverted forefoot relative to rearfoot is caused by a talar head which is rotated or if it is caused by a forefoot inverted at the talus / nav joint, the nav / cuniform joint or the cuniform / met joint? -
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Phil Wells would be better explaining it than me. he calls it the "new first ray cut out" that Salts can do. Not sure if it is new, but I have utilised it quite a bit with some success. It's not impossible in the traditional fabrication method but requires a lot of plaster modification. -
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OK, back to the plot... are there any published studies which demonstrate a reduction in first metatarsophalangeal joint dorsiflexion in association with foot orthotics, other than the Kilmartin study I mentioned above, which showed a 2 degree reduction (and I can't remember if they took into account the heel lift effects of the devices in this study, which was a key weakness in ours :eek:)?
For example, do we have any studies looking at the kinematics of the 1st MTPJ in association with Morton's extensions? -
Not that I know of.
But my new toy arrived yesterday so if you want to do a kinetic (kinematics, pfft) study in static WB along the lines we discussed, using a mortons extension and testing 1st met stiffness with and without, it could be done without too much difficulty. I have some calibration to do but that should not be too hard... -
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It does make you wonder.
Eric -
BTW I have an antique measuring device that my old boss gave to me, I'll take a photo and post it up.
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