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Forefoot medial posted orthoses do not reduce hallux dorsiflexion

Discussion in 'Biomechanics, Sports and Foot orthoses' started by David Smith, Feb 13, 2016.

  1. David Smith

    David Smith Well-Known Member

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    Reading Michaud's Human Locomotion chpt 8 states that f/foot Medially posted orthoses do not reduce hallux dorsiflexion in propulsive phase of gait i.e. they do not inhibit windlass action and cause FncHL.

    "Although it was originally believed that elevating the 1st metatarsal head during propulsion would produce functional hallux limitus, a kinematic study by Nawoczenski D (2004 JOSPT)et al has shown this is not the case". (Michaud Human Locomotion Chpt 8 pge 349)

    However the conclusion of the paper states that:
    "Foot orthoses that incorporate a medial forefoot post do not have a consistent negative effect of reducing first MTP joint dorsiflexion during walking".

    Not consistent, sometimes it did and sometimes it didn't, doesn't mean not the case at all.

    Therefore it seems Michaud has abstracted more from the conclusion than the authors intended.

    But: Having read the Nawoczenski paper it appears there are there are some errors in the methodology that would make the conclusions from the results erroneous.

    First it is a mechanical fact that dorsiflexing the 1st ray, about the proximal joints, causes plantarflexion of the hallux due the windlass mechanism. Merely elevating the 1st metatarsal relative to the ground does not necessarily dorsiflex the 1st ray e.g. inverting the stj. Dorsiflexion of the 1st ray in itself will not necessarily cause FncHL unless there is sufficient force sub 1st MPJ i.e. there must be a consideration of the balance of moments about the 1st MPJ and the proximal 1st ray joints.

    The Nawoczenski paper's inclusion criteria include a f/foot varus of 10dgs+ (which seems exceptional in itself and probably (almost certainly) includes supinatus and they do not appear to distinguish between flexible or rigid deformations.

    "The supination of the forefoot that develops with adult acquired flatfoot is defined as forefoot supinatus. This deformity is an acquired soft tissue adaptation in which the forefoot is inverted on the rearfoot. Forefoot supinatus is a reducible deformity. Forefoot supinatus can mimic, and often be mistaken for, a forefoot varus. A forefoot varus differs from forefoot supinatus in that a forefoot varus is a congenital osseous deformity that induces subtalar joint pronation, whereas forefoot supinatus is acquired and develops because of subtalar joint pronation. " Evans EL et al 2014.

    This apparent oversight in itself would render the results meaningless because the mechanical variations between varus and supinatus, flexible and rigid would inevitably result in variable outcomes whereby the effect of forefoot medial posting would inevitably not be consistent.

    The second main error is that unless the forefoot posting significantly increased GRF sub 1st MPJ and concomitant increased hallux plantarflexion moments and 1st ray dorsiflexion moments then it is inevitable that there would be no significant change in hallux dorsiflexion or increase in FncHL.

    The third apparent error is that they may be measuring the relative change in range of motion between hallux and 1st ray but not the absolute dorsiflexion range relative to the 1st ray. This might be especially true in the non posted high arched orthotic condition where the change in the 1st ray declination angle is the greatest when compared to the no orthotic condition.

    So if the 1st ray is more plantarflexed at initial state then the initial state of the hallux is more relatively dorsiflexed but it may be that during propulsive phase the actual relative change or increase in hallux dorsiflexion is no more than the non orthotic condition. However the windlass action will more likely be inhibited in the non orthotic condition than the orthotic condition in either medially posted or high arched types. Therefore the relative change in hallux dorsiflexion is irrelevant to the prediction of the presence of FncHL.

    The fourth error IMO is the consideration of kinematic over Kinetics.

    I don't think Michaud should have put so much faith in this paper and one wonders why he did not consider the evidence of many other papers that would have the opposite conclusion that high forces sub 1st MPJ concomitant with 1st ray dorsiflexion results in increased potential to FncHL or the other perspective - reducing the GRF sub 1st MPJ will reduce the possibility of FncHL.

    It is possible I may have misinterpreted the Nawoczenski paper because its a difficult read, its very techno speak, not written in clear language.

    Just putting these thought down because this is an important principle when considering foot pathology and orthosis design and this book 'Human Locomotion' is used by many student podiatrists who may be misled by this (erroneous) statement.
  2. drhunt1

    drhunt1 Well-Known Member

    David-thanks for the links...I shall read them later. It happens to follow some of the conclusions I reached while attempting to successfully treat growing pains in children, and RLS in adults. I extended the forefoot varus correction, (medial correction), to the end of the toes, thus allowing for FHL tendon insertion purchase. It just makes sense to me. http://www.podiatrym.com/Biomechanics_Footwear_Sports_Podiatry2.cfm?id=1632
  3. David Smith

    David Smith Well-Known Member

    Is RLS restless leg syndrome? Do you think restless leg syndrome has a mechanical aetiology? What do you mean by growing pains? are you referring to Osgood schlatter syndrome?Or the non-inflammatory musculoskeletal pain syndrome of Juvenile recurrent nocturnal limb pain?

    I'm not sure that GPs or RLS can be addressed with a mechanical intervention, what's your theory here?

    As far as the f/foot medial posting is concerned, yes I often use posts extended to the MPJ's or toes depending on the tissue stress disorder I'm addressing and the inherent biomechanical status of the subject of interest.

    Cheers Dave Smith
  4. drhunt1

    drhunt1 Well-Known Member

    RLS=restless leg syndrome, or periodic nocturnal limb movement, or whatever the latest "flavor" may be. I believe that the majority of RLS and GP's are a continuum of the same problem...which is referred pain from the STJ. The cause is STJ subluxation with normal activities during the day creating a transient synovitis after retiring for the evening. As described in my pilot, case study, the clinical test is quite easy to perform in those patients that are symptomatic. And yes, the treatment for both maladies is a "mechanical" device...an orthotic that prevents the patient from maximum eversion at the STJ, thus preventing subluxation. In my article, I showed an example of the medial post extension I'm ordering...it extends out to the insertion of the FHL tendon. The hallux, in my opinion, is THE most important digit in the foot...responsible for the majority of propulsion and balance. It only makes sense to me to extend the medial varus correction to "bring the ground up to the hallux", in order to offer more normal foot/leg function. Your post/research only confirms what I have discovered on my own. Thanks.

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