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What causes HAV?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Robertisaacs, Dec 1, 2007.


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    A simple and possibly question. I suspect the answer to be less so.
     
  2. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    WARNING: TURNING ON RANT MODE...

    We have to stop talking about causes. For most things we see do not have CAUSES. They have things that increase the risk of happening. A pronated foot causes nothing, all it does is potentially increase the risk for many things (but even thats debatable!). I can never work out why we still do it (I published something on this 10 yrs ago). Smoking does not cause lung cancer, it increases the risk of lung cancer (not all smoker get lung cancer). Dyslipidaemia does not cause ischaemic heart disease, it increases the risk for it (not all with dyslipidaemia get heart disease). Peripheral neuropathy does not cause foot ulcersm it increases teh risk for it (not all with neuropathy get foot ulcers).

    You should have asked, what are the risk factors for HAV?

    RANT MODE OFF
     
  3. Admin2

    Admin2 Administrator Staff Member

  4. Bad day craig?:rolleyes:

    Ok. What are the risk factors for HAV?

    I suppose i should be more specific still.

    There seems to be an inherited element to HAV. That is mainly agreed.
    Simon said on one of the other threads that the formation of HAV was thought to be multifactorial and that
    Thats fine.

    What are the factors?

    When somebody has had 1st ray surgery what are the forces / factors we should be seeking to control to reduce the risk of the deformity recurring? Why? Is there any evidence / models / beleif that by controlling any environmental factors / forces we can reduce the risk / speed of a deformity developing? If so what and why?

    Sorry if i am asking stupid questions here but i am presently going through a process of questioning things i had taken for granted and this is one of them.

    Regards
    Robert
     
  5. Craig and Robert:

    I agree with Craig that the term "risk factor" is a much better term to describe the possible causative factors that may lead to a pathology, such as hallux abducto valgus deformity. However, when one analyzes the dictionary definitions of "cause" or "causation"
    then using Robert's use of the term "cause" is understandable since we know that a risk factor is simply a factor that may possibly cause an effect.

    Over the past 22 years, about 30% of my practice has been work-related injuries. In the world of industrial injuries and its associated medical-legal jargon, the term "causation" is a commonly used term that is defined as whether the injury could have been caused by the patient's alleged work or work-related accident. The term "risk factor" is not used in the worker's compensation courts but the term "causation" is accepted and encouraged.

    Therefore, it certainly seems that some latitude should be given for the use of the terms "possible cause" or "causation" especially when we are discussing the nature of various musculoskeletal injuries and pathologies in a medical-legal setting, such as in a patient's chart or during a deposition on a work-related injury. However, in a scientific setting, such as we have here on Podiatry Arena, Craig is right that the term "risk factor" is a much more appropriate term to describe the possible causes of a given pathology.
     
  6. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    The only true way to determine the extent of a risk factor is a prospective study...a group of people who do not have a particular condition have data collected on a whole lot of variables and then followed through time. Over time, some will develop the condition and some will not. The varibles measured at baseline are then compared in the groups that did and did not develop the condition to see which variables are more common in which group (ie which are risk factors and which are protective factors).

    As for HAV, we do not have that data, but we do know enough to know which variable should be studies as part of a prospective study.

    Footwear is an obvious one. Inappropriate footwear does not cause HAV, otherwise why do all those who wear inappropriate footwear not get it. HAV also occurs in non-shod populations, but HAV is more common in shod population s.... because of this we can NOT claim footwear cause HAV, but inappropriate footwear obviously increases the risk.

    HAV is more common in females --- but we have no idea if being female is the risk factor or is it that females are more likely to wear inappropriate footwear. It always amazes me the sweeping "factual" statements made on this, when we really just do not know. We do not know in females if its footwear, if its hormonal, if it a pelvic width thing, or etc

    Mert Root, in Vol 2 gave us a very plausible and coherent pathological mechanism by which HAV could be caused by exscessive rearfoot pronation ... but thats all it was, just plausible and coherent pathological mechanism. It is interesting that the profession ran with this as "the cause" (I was one of them!).

    The alleged evidence as to a pronated foot --> first ray hypermobility --> subluxation at first MPJ --> causes HAV , is that several studies have shown that HAV is more common in flat/pronated feet .... BUT they were cross-sectional and only simply showed that HAV is more common in flat/pronated feet .... they DID NOT show that the flat/pronated feet caused that HAV .... it would be equally plausible to conclude that people develop HAV; that then causes a medial column weakness; that then causes the foot to pronate. Given that non-shoe wearing populations develop HAV (in small numbers), mechanical factors would be logically included in a prospective study.

    Other mechanical factors that have the potential be to included would be things like met head shape; lack of the reverse windlass (and hallux purchase moments); activity of the abductor hallucis muscle; etc

    Obviously genetic factors play a role, but are they just things like the shape of the first met head etc .....
     
    Last edited: Dec 2, 2007
  7. W J Liggins

    W J Liggins Well-Known Member

    I was speaking to an orthopod who presented a lecture on the subject two weeks ago. He re-iterated the shod/non shod factor and the 'females shoes are worse than males shoes because they press the hallux medially' scenario. It was clear that he had not considered that shod cultures tend to ambulate on hard, flat surfaces, whilst unshod tend to walk on undulating surfaces on which the foot (arguably) functions better. He fully accepted this argument together with another factor which is that current female footwear styles tend towards the pointed toe, which creates an unstable medial border, hence increasing the likelyhood of medial toe off.

    The problem is clearly multi-factoral, and I quite agree that prospective long term investigations will be the only method of eliminating the variables. Any takers? (I'm too old).

    Bill Liggins
     
  8. Thankyou, Craig, for a very complete answer. I was hoping that you or one of the other of the "inner circle" might have a crack at that one.

    Along with most of the rest of the profession i had always run with the "we-don't-really-know-but-we-think-its-something-to-do-with-pronation model, however it occurred to me that i did not really fully understand the mechanism. (do any of us?)

    Its often hard to untangle causes and effects in biomechanics. Obviously this is one of those times where we have a model and a correlation and the space in between filled with reasonable assumptions.

    This one is for anyone.

    Do you ever issue insoles with the intention / claim to reduce the chance of an HAV developing?

    Thanks again
    Robert
     
  9. W J Liggins

    W J Liggins Well-Known Member

    Worth having a look at Tim Kilmartin's PhD paper which showed that following the protocols he used and the use of the relevant devices, that the null hypothesis was proven. ie. that in the children studied, orthoses increased the likelyhood of H/A/V.

    The problem is, as Craig outlined, since we do not know what causes the problem, neither do we know how to prevent it.

    Bill Liggins
     
  10. Thanks Bill. I don't suppose you have any idea how i might get eyes on that paper (or even the edited highlights). Was there anything published?

    Cheers
    Robert
     
  11. Robert,

    Why not pop along to the British Library and read my book on this subject:

    Spooner S.K. 1997: Predictors of Hallux Valgus: A study of heritability. PhD Thesis, University of Leicester.

    Also, I seem to remember the biomechanical models by Sanders and Snijders as being interesting.
     
  12. W J Liggins

    W J Liggins Well-Known Member

    Hello Robert

    I don't have the references to the several papers by Kilmartin but he can be contacted at Ilkeston Hospital, Heanor Road, Ilkeston, Derbys. DE7 8LN. Tel. 0115 932 5834.

    All the best

    Bill
     
  13. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    While we do not necessarily know what causes HAV and if the 'pronated foot' model causes HAV (or if HAV causes the pronated foot) and while we do not necessarily have the data from prospective risk factor studies or prospective intervention or prevention studies, we still have to make clinical decisions and give clinical advice.

    I think we can safely deduce that HAV is associated with inherited factors (that cause structural and functional changes) and environmental factors (footwear; perhaps hard surfaces). I think we can safely say that footwear is not a cause (otherwise why do non-shoe wearing population get it?), but the way I explain it to patients (in the absense of data) is that inappropriate footwear may play a role in bringing it on earlier, may cause a faster rate of development, may result in a worse eventual outcome and is certainly responsible for the resistance that causes the symptoms.

    Not me, but have heard many strong assertive arguments from some who claim to have seen the equivalent of a radiographic regression of HAV with foot orthotics (especially if you use "their" type of orthotic). I do not deny that it can happen, it just that strong nature of the claim in the absense of data. I would only want to use them for HAV/bunions if there was more going on than just the HAV/bunions - that does not mean that they will not provide symptomatic relief if functional problems were causing the symptoms
     
  14. Robert,
    See here:http://www.footsurgeryservices.com/a-publicaton.htm

    Timmy K he a busy boy! "Glad to see my face among them" Bunnymen
     
    Last edited: Dec 3, 2007
  15. efuller

    efuller MVP

    Hi Craig,

    This is a very interesting are for me to think about. I'm having a fight between the mechanical engineer in me and the clinician in me. I certainly see the point about risk factors when there are many unknowns. However, it may be possible to know what the cause is. If you look at sickle cell anemia, you can say that there is a gentic risk factor. However, the gene has been isolated and the speicific amino acid change has been identified. The mechanism by which the Hemoglobin molecules become sticky and cause the red blood cells to sickle is known. I think that is a case where the cause of clinical condition is known.

    In terms of HAV we can look at the history of the foot and see that at one point the toe was straight and the toe that we are looking at now is not. Something caused it to change its position. F = ma. Moment = moment of inertia x angular acceleration. So, if we are going to look for a cause then we are going to have to look at forces and moments.

    Actually, I don't feel that the propsed mechanism in Noramal and Abnormal function of the foot is coherent. I've read through it mutiple times and it still does not make sense to me.

    For what I think "causes" HAV see

    Fuller, E.A. The Windlass Mechanism Of The Foot: A Mechanical Model To Explain Pathology J Am Podiatr Med Assoc 2000 Jan; 90(1) p 35-46
    It is an expansion of the snijders and sanders papers that Siomn referred to. It also refers to the "reverse buckling" phenomenon described by McGlamry.

    Sanders AP, Snijders CJ, van Linge B. Medial deviation of the first metatarsal head as a result of flexion forces in hallux valgus. Foot Ankle 1992 Nov;13(9):515-522

    Snijders CJ, Snijder JG, Philippens MM Foot Ankle 1986 Aug;7(1):26-39 Biomechanics of hallux valgus and spread foot.

    Sanders AP, Snijders CJ, Linge BV Potential for recurrence of hallux valgus after a modified Hohmann osteotomy: a biomechanical analysis. Foot Ankle Int 1995 Jun;16(6):351-356

    There are two kinds of research to do. Correlational research and basic science research. They are both needed. The correletional research will identify the risk factors. The basic science research can figure how the correlational things interact to be causative.

    Regards,

    Eric
     
    Last edited: Dec 3, 2007
  16. Interestingly, the study of Johnston that I mentioned here:
    http://www.podiatry-arena.com/podiatry-forum/showthread.php?goto=newpost&t=3900

    Showed lots of individuals with hallux valgus without concomittant "pes planus".

    Kalen and Brecher (1988) reported no correlation between hallux valgus and calcaneal inclination angles and dorsoplantar talo-navicular angles.

    Kilmartin and Wallace (1992) compared arch index measures between normal and juvenile HV feet and found no sig diff.

    As for Root's theory: Inman (1974), D'Amico and Schuster (1979) and Oldenbrook and Smith (1979) disputed the theory of first ray motion proposed by Root et al. (1977). They suggested that the "hypermobile" first ray everted when dorsiflexed, and assumed the hallux underwent the same motion! :morning:
     
  17. Thanks to all, especially simon for your help and some valuable references for me to chase.

    The next time i'm in the british library i shall be sure to have a butchers. ;) Its a sod of a way to got to read a book though (as worth it as i'm certain it its!)

    Thanks again

    Robert
     
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