Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

Abducted hallux

Discussion in 'Biomechanics, Sports and Foot orthoses' started by David Smith, Oct 21, 2009.

  1. David Smith

    David Smith Well-Known Member


    Members do not see these Ads. Sign Up.
    Hi All

    Got a customer with a type of foot that has me wondering how to prescribe her orthoses and so I thought I would ask for some advice here.

    Lady 66yrs old, painful ankles lateral but mainly concerned about waddling gait.

    2 x hip replacement.

    Both feet - STJ 30dgs inversion and 3-5 dgs eversion,

    max STJ pronation in gait and stance,

    navicular drop 10mm drift 15mm i.e. forefoot abducted on rearfoot.

    Left STJ axis extremely medial and medially rotated, right STJ axis medial,

    left leg external femoral torsion = hip neutral is ext rotated ie knee mid range RoM = 35dgs ext rotated and there is no internal rotation available past knee straight ahead.

    right leg 15-20mm longer than left by measuring GT to malleolous.

    High right hip and illac crest, level ASIS.

    In gait foot placement is toe out 30dgs left and straight ahead right.

    Rocks onto left side during right swing thru,

    very weak left hip abductors by manual testing.

    In stance and especially in gait left foot hallux abducts (away from the foot midline) by 12-15dgs

    The ankles are painful due to the internal stress resisting pronation and tibial torsion. The waddling gait is mainly due to weak left hip abductors - NB when she uses her stick in the right hand she stabilises frontal plane moments about the left hip and by applying balancing GRF thru the stick and so does not waddle.

    The hallux abducts to add stj supination moments in a foot that is toe out externally rotated and abducted with a medial STJ axis, i.e. everything is trying to pronate the foot past max RoM.

    It is also interesting to note that and shoe insole template overlaid over her foot print on a podotrack shows that when barefoot her hallux abducts way outside the shoe confines. One might imagine therefore that STJ pronation moments are not as well resisted by hallux GRF andthere would be greater stress in the internal tissues at max pronation. A shoe with a really wide forefoot might be advantageous here except that this will encourage the hallux abductus deformation??

    My query here is how to design an orthosis that will encourage the hallux not to abduct but not significantly internally rotate the left foot placement angle since this would lead to torsional stress in the knee at right swing thru if there was insufficient relative hip internal rotation available at this time.

    For the left foot I was thinking of a deep medial skive with a high medial arch flange and an excessively wide forefoot on a shank independent shell orthosis with balance heel lift . Fitted in a shoe with a wide forefoot.

    Any thoughts?

    Regards Dave
     
  2. Surely the shoe will prevent the hallux "abduction" from the midline of the foot.
     
  3. David Smith

    David Smith Well-Known Member

    Well yes but the muscular action that will tend to abduct the hallux will still operate but there will be no increase in supination moment arm. I need the orthosis to take over this action and obviate the need to do this with the hallux. I'm wondering if this is something anyone has tried before ie making the forefoot of the orthosis extra wide to increase the supination moment arm and via the torsional stress in the orthosis increase orthotic reaction force (ORF) at the medial skive aspect of the heel and arch?

    Kind of answering my own questions as I go alone but appreciate your input.

    Dave
     
  4. Maybe, but why do we see a reduction in internal supination moment in association with foot orthoses if not through an alteration in muscular activity? You could argue thast opposing external moment against the hallux from the shoe or a foot orthosis might increase the muscular action you note above, but it might also reduce it, who knows? taking you argument above re: supination moment arm, you can alter supination moment about the STJ axis (I assume this is what you are talking about) with standard shell modifications eg. medial heel skive, internal oblique rearfoot post etc
     
  5. Boots n all

    Boots n all Well-Known Member

    l would be at least (if you dont go with custom shoes) a custom soling.

    Left foot "sounds like" it needs a lateral flare and a rocker sole with the fulcrum set at the 30dg abduction you describe, this will cause less pressure/force required to move through the stand and propulsive phase and may well result in less abduction moment of the Hallux.
    Example; The fulcrum line of the rocker might run from the distal 5th to the MPJ of the 1st ?

    Still do the orthosis but how much correction can you give a 66 year old that has had two hip replacements etc, etc?
     
  6. efuller

    efuller MVP

    Is the pain in the sinus tarsi? From everything else it seems like it should be.

    Post hip replacement with some odd hip ROM numbers. I would be thinking that the hip numbers are related to the hip surgery.
    It sounds like the gait is related to weak hip abductors which may not have fully recovered post hip surgery. You mentioned that they were weak, perhaps some muscle strengthening. Especially since the waddling is her main concern.

    The reverse windlass can cause the hallux to go toward the midline of the foot or away from the midline. Most go toward the midline, but away can also happen. The tension in the fascia and plantar intrinsics (the stuff attached to the sesamoids will cause a rearward force on the proximal phalanx. If this force is not directly in line with the force from the metatarsal acting on the phalanx, you will get a force couple that will tend to cause rotation of the hallux in the transverse plane. So, I wouldn't say that the toe abducts to add supination moments. I would say that internal pronation moments would casue the fascia to be tight and this causes the toe abduction.

    When the shoe holds the toe in, there will be less motion of the arch of the windlass, and this may alow the windlass to add more supination moment when compared to barefoot. If it's not uncomfortable I would keep the forefoot of the shoe narrow.

    It sounds like you are thinking the pain in the ankles is because of pronation to end of range of motion.

    Decreasing tension in the fascia will help reduce hallux abduction.

    I feel that the angle of gait is "chosen" by the patient. That is the patient will put their foot on the floor in the angle where they find the most comfort within their range of motion. So, if your foot device altered their choice of foot placement, I think they would still choose an angle that would not place stress on the hip. Things will change if they are so far internal that during swing, their swing foot hits their stance leg and they trip. (Not a problem in this case.) An orthosis cannot enforce angle of foot placement as it does not contact the ground during swing, nor does it grab on to the leg.

    I like the heel lift as the limb length descrepency could be the result of the hip surgeries. You could try the old phone book test where you stand the patient with the short leg on the phone book and flip through the pages until they "feel" level and measure that height for your lift. I also like the medial heel skive to decrease tension in the fascia and decrease internal forces in the sinus tarsi. As long as the shoe is not uncomfortable, I would not get her an extra wide shoe to allow the toe to abdcut. There are pros and cons of shank dependent devices. The physical exam you gave did not tilt the scales one way or the other on using a shank dependent device.

    Hope this helps,
    Eric
     
  7. David Smith

    David Smith Well-Known Member

    Boots and Eric

    Like the angled rocker idea but compliance might be an issue

    Good Stuff thanks very much

    Dave
     
  8. Dave:

    Sorry....coming on a little late on this thread. I pretty much agree with everything that Simon and Eric have said.

    The plantar fascia is probably the main source of the internal hallux abduction moment, which is, of course, a passive force, not an active one. The abductor hallucis obviously has more mechanical advantage to cause hallux abduction than the medial slip of the central component of the plantar aponeurosis (i.e. plantar fascia), but the plantar fascia probably develops at least 10 times more tensile loading force within it than does the abductor hallucis during the stance phase of gait.

    I would try to use the shoe to resist further hallux abduction since these deformities (i.e. hallux varus) will tend to get worse over time. However, too much external hallux adduction force from the shoe can cause medial hallux irritation, so the patient may try getting a leather upper shoe with a normally shaped toe box initially that can then be stretched a little bit if hallux irritation develops. Otherwise, your initial orthosis design recommendations seem reasonable to me. As far as angle of gait, this is most likely related to her transverse plane hip position.

    One of the tests I have used for many years, and I demonstrate regularly to the podiatric surgical residents that rotate through my office, is to have the patient lie flat on the table (i.e. plinth), and then internally and externally rotate both limbs (by grasping the ankles) and find the position where the hips "want" to lie in (trying to eliminate the rotational effects of gravitational acceleration on the mass of the feet). The knee and foot angles are noted here and correlated to their position during stance and gait. I find this test gives me a better idea of the internal transverse plane rotational moments from the soft tissue acting across the hip joints of the patient that are important factors in determining their self-selected angle of gait.

    Good luck with this interesting case.
     
  9. Boots n all

    Boots n all Well-Known Member

    "Like the angled rocker idea but compliance might be an issue"

    Its not that noticeable and the pressure relief for the client will amaze you both.

    We use this method where needed, one client we were able to allow a 3 year old pressure wound over the navicular to heal, just by reducing the pressure/force used to move the foot through the propulsive phase of gait, which for her is just proximal of her 1st MPJ.
    The client is so effected by arthritis no change of the joints position was possible.

    l would post a pic of the feet up, but both my tech adviser are studying for exams at the moment......i hope :hammer:hope
     
  10. efuller

    efuller MVP


    Are you saying that the abducted hallux will put more foot in a more medial position relative to the STJ axis. The assumption is that there is significant amount of force on the hallux for a significant amount of time. I'm not sure that you are getting that much movement of the center of pressure with abduction of the hallux.


    It will increase tension in the plantar fascia sooner. That is the fascia will become tight in both situations but the arch will flatten more and the STJ will pronate more before the fascia becomes tight. Probably not that big of a difference. The issue that Kevin mentioned, increasing of the abduction deformity, is a better reason to keep the shoe from being too wide.



    I do see a lot of "pronated" feet that walk abducted. However, I don't think there is a cause and effect there. What torsional stresses are going to increase pronation moment that will increase pain in the sinus tarsi.


    I agree not because the varus wedge effect is better, but because the heel tends to slide down the varus wedge and needs the lateral heel cup to prevent sliding. A soft device has difficulty doing that and needs a solid heel counter of the shoe to do it.

    Regards,

    Eric
     
  11. David Smith

    David Smith Well-Known Member

    All very interesting

    Cheers Dave
     
  12. efuller

    efuller MVP

    There are many possible explanations for the difference between right and left in the pressure scans. I would question that they even have the same amount of total force on each foot. I would question whether the center of pressure is drastically different. Even if the left foot is more supinated you would not know if that supination moment came from the windlass or muscles.






    At what point in gait are you describing above. When I think of breaking forces I usually think of heel contact phase, however I could see how you could be describing the entire first half of the stance phase when there is an anterior to posterior shear on the stance foot.

    At heel contact, with the foot abdcuted from the midline the anterior to posterior shear will be on the posterior heel which would tend to be closer to the mdiline of the body than the leg so there would be an eccentric force tending to internally rotate leg at this point in time. However, this would change after forefoot loading. At that point in time there will be anterior to posterior shear on the forefoot and the heel. It would be hard to say what the next internal or external moment on limb would be.

    Interesting to think about, but so many variables.


    Regards,
    Eric
     
  13. David Smith

    David Smith Well-Known Member

    Yes I agree but if we make certain assumptions then;

    This vertical force graph shows total force (Red), heel force (thin red), forefoot force (blue), 1st MPJ force (green), hallux force (purple). I would say that braking ends at about 425ms of the 800ms stance phase. The fore foot loading is quite significant if you consider the forefoot has a longer moment arm than the heel. In fact at this time CoP is just behind the 3rd MPJ and max pressure is over the 2nd MPJ.

    [​IMG]

    If we consider this diagram then it can be imagined how the moments about the STJ and ankle joint might be. (assuming experienced based proportional relationship of horizontal to vertical forces) Like you say its all interesting speculation. (oh! and the point of application of the forces in the diagrams is the same as the vertical CoP position for that time and the dashed arrow in the 3D diagram is the GRF vector pointing 12dgs lateral and 35dgs posterior.)

    [​IMG] [​IMG]

    Cheers Dave
     
  14. efuller

    efuller MVP

    Let's double check our definitions. I've heard breaking force defined as force, in the transverse plane, from anterior to posteior appliled by the ground to the foot. The reason that there is a breaking force is that the center of mass is posterior to the center of pressure under the foot. If this force were not present the foot would slide and you couldn't get the body to rotate forward over the stance foot. Looking at classic anterior posterior force outputs for a step, the magnitude of the ant post forces at maximum are about 10% of vertical forces. Also they reduce to zero as the body is directly above the center of pressure and switch direction so that after the center of mass passes the center of pressure the a-p forces are from anterior to posterior for the force from the ground applied to the foot.

    It would be an unusual gait that would still have force from the ground being from anterior to posterior after heel lift. The time you describe is right about heel lift as the heel forces are close to zero. So, the a-p forces should be close to zero at this point in time (425ms).



    I can't remember the articles where I read it, but the medial to lateral forces on the foot in gait were about 1% of vertical forces. They have the same cause as the a-p horizontal forces. In midstance the center of pressure is lateral to the center of mass. (This force couple causes the body to fall back toward the contralateral foot.) So, the direction of force is from lateral to medial acting on the foot at this point in time for a force from the ground acting on the foot. (For novices following along this illustrates how important it is to properly label the forces because there is an equal and opposite reaction occuring at the foot floor interface. There is a lateral to medial force from ground acting on the foot and there is a medial to lateral force from the foot acting on the ground.) So ground reaction force at midstance, if applied at the center of pressure just proximal to the third met head would tend to cause internal rotation of the leg using the logic of the diagram. (The vertical force in the diagram is upward and that would imply that it is the force from the ground acting on the foot. Therefore the medial to lateral force in the diagram should be in the oppositte direction than it is drawn.) The logic assumes the inertial forces are at the talar dome, and I'm not sure that you can do that.

    Cheers,

    Eric
     
  15. David Smith

    David Smith Well-Known Member

    Eric

    Oh yes made a bit of a faux par there, you are quite right about the horizontal forces at 425ms, in my casual haste I confused the issue. The End of braking is at around 425ms but the CoP position I should have showed was at 325ms which is about 20mm posterior to the 425 position. At this position the GRF forces I assume would be about right. The principle remains the same tho in my opinion.

    In a standard type gait cycle max vertical forces are 120% body weight A-P forces 20 - 30% body weight and M-L forces 5-10% body weight. But these are only standard guides and these force values change dramatically relative to the style of gait.

    Certainly in a standard gait that is true but in this type of gait the lateral forces tend to last longer into the cycle, but this is the problem with making assumptions about GRF forces without real data and you may be right that the M-L force is medial in direction at this time. In the reference frame of the foot the forces would more tend to be lateral in direction but in the global reference frame the forces may be medial. I think my mistake is that I'm thinking local frame and drawing global frame.

    My main point was that the foot that is toe out in placement will tend to have GRF that tend to externally rotate the foot and so cause a relative internal rotation of the tibia, this coupled with the braking forces will tend to pronate the foot more than a foot placement that is straight ahead. Also that abducting the hallux (away from the foot midline) will add significant supination moments about the STJ.

    From what you have said it seems that you disagree with this synopsis and considering your reasons for these proposals is useful in consideration of orthotic design for my patient, which was the purpose of this thread. Thanks Eric and all.

    All the best Dave
     
Loading...

Share This Page