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Is a leg length difference in runners really a problem?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Nov 20, 2012.

  1. Craig Payne

    Craig Payne Moderator


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    We have had plenty of threads on leg length differences, but many things really bug me about the concepts. For eg, the concept of foot pronation as a compensation for a structural LLD has been debunked, but what about this:

    If someone has a structural LLD and they are standing with feet side by side, the body can probably detect the difference and compensate for it.

    BUT, when running there is only ever a single limb support phase and there is no phase in which both legs are in contact with the ground (let alone side-by-side). If there is only single limb support, how does the body know that one leg is shorter or longer than the other and it should compensate for it??? (let alone increase the risk for injury).

    This has been alluded to in a couple of other threads, but probably deserves airing on its own.

    Obviously I talking about the more subtle LLD's and not the really big ones. I also only talking about a structural LLD and not the functional ones due to, for eg, asymmetrical foot pronation or more proximal problems in the hip and SI joint.

    I do recall Howard D a few yrs back suggesting that the body detects this, by way of analogy, "having a bigger hump to drive over on the longer side".

    Is a subtle LLD in runners a problem or not? What say you?
  2. efuller

    efuller MVP

    So, if you have a 1/4" limb length discrepency and say your stride length is 33" then your fall or rise is less than a running on a 1% grade. Barely noticeable. 33" is a walking stride length. Running is what 1.5 times that? So, the leg length difference would be like running up, or down, a very minimal incline.

  3. Craig Payne

    Craig Payne Moderator

    Would that be sufficient to cause pathological compensations and increase the risk for injury? I not suggesting that its not, I just need to be convinced that it is.

    Some clinicians from a number of different professions have some extreme obsessions about small LLD's being extremely important, but is it?
  4. Paul Bowles

    Paul Bowles Well-Known Member

    If pathomechanical injury is all force related in it aetiology what eric says above makes complete sense.
  5. sesadler

    sesadler Member

    Yes. Yes, they do. (Have extreme obsessions.)

    My initial thoughts are that for the minor differences (up to ~9mm / ~3/8") that
    it's not 'extremely' important. However, I am continually amazed at the number of patients that express relief on in shoe wedges or full sole lifts of up to 3mm while running. They swear that without it they are unable to perform without discomfort.

    So perhaps a modification of the question might be: how important is it to try and hit an exact measurement for these runners?

    I have one doctor than sends me 3-5 patients / week for heel wedges ranging from 2mm to 21mm. Some have had success and others have said with time it made things worse.

    More exploration on this!

  6. if you think in leg stiffness sense

    As a compensation mechanism

    the longer leg may have lower stiffness as a compensation mechanism to control the progression of CoP.

    only if the body functions out of it physiological window - longer leg reduced leg stiffness increased chance of soft tissue injury.

    But as the person has functioned with this for a life time generally I doubt it wold be an issue due to adaption.
  7. docbourke

    docbourke Active Member

    It seems everyone is looking at the problem arse about. Instead of theorising whether a leg length discrepancy causes pathology why not take a group of runners at an event and accurately measure their leg lengths then do a quick training questionnaire to see if the athletes with a LLD have more injuries than those without.

    I might also look at the pedobarographs of athletes with known LLD whilst running and determine if there is more asymmetry than those without. Remember that most runners have a reasonable amount of asymmetry and stride variation anyway so I suspect the body can't pick a subtle change.

    Observation and study will always be the shortest route to the truth rather than unfounded hypothesis that will simply muddy the waters and create controversy.

  8. say take a portable xray machine with you ;)
  9. docbourke

    docbourke Active Member

    A portable CT would be better. Anyone got one I could borrow.;)
  10. Craig Payne

    Craig Payne Moderator

    There are these studies:
    No increase in injury in those with leg length difference in a military population and LLD did not increase the risk for overuse injury or low back pain.
    Leg length discrepancies in elite track and field athletes with stress fractures and LLD appears to increase risk for stress fractures in elite athletes
    Limb-Length Discrepancy as a Cause of Plantar Fasciitis

    The first one is prospective and the later two fall into the correlation v causation trap.
  11. I tend to concur with Mike. My hypothesis is that the body has a preferred movement pathway for the centre of mass (COM) during running at a given velocity; running with a limb length discrepancy should tend to cause an asymmetrical displacement pathway for the COM; to compensate for this, the body will modulate the leg stiffness by either decreasing the stiffness of the longer limb and/or increasing the stiffness of the shorter limb. As Mike intimated, if the tissues are able to do this while functioning within their zones of optimal stress (ZOOS), injury may not ensue. However, if in order to maintain the displacement pathway of the COM, the tissues are forced to function outside of their ZOOS, then tissue injury may occur. If the contentions of Butler et al. are correct ( http://www.udel.edu/PT/davis/stiffness_update.pdf ) then a leg which is functioning too stiff for the environmental and task demands may be at greater risk of bony injury, while a leg which is functioning too compliant for the environmental and task demands may be more prone to soft-tissue injuries.

    This is why I think asymmetrical density heel raises may be helpful in limb length discrepancy.
  12. Paul Bowles

    Paul Bowles Well-Known Member

    ...because what would that show? Correlation? May as well take the same group of runners and check what hair colour they have and then do a quick training questionnaire and see how hair colour relates to injury. I'm going to take a wild guess and say that hair colour would cause as much injuries as LLD in this cohort. The evil side of my brain is thinking that the "gingers" should have more injuries though....... ;)

    This raises an interesting point - we are not symmetrical beings. Does anyone have any research on asymmetry and pathomecahnical injury rates? I would argue asymmetry is completely normal but that's just my clinical opinion.

    Just because a clinician has seen thousands of cases and managed them over the years doesn't mean what they were doing was right or the truth. There are many examples of this in daily clinical practice where we do something because it is dogmatic and observational.
  13. I read somewhere once that elite athletes are more symmetrical than non-elites, don't ask me where. Also of note here is that symmetry changes with hormonal cycles, at least in terms of facial symmetry among adult females- they are most symmetrical when fertile- again, I read that somewhere once...

    In terms of pressure readings in limb length discrepancy- chatting to Bruce Williams at the ACFAOM meeting in Florida 2011, he suggested the association between higher loading response pressures on the shorter limb side- this would fit with the hypothesis of higher leg stiffness on the shorter limb side.
  14. To answer Craig's original question, yes, leg length discrepancy (LLD) can be a problem in runners and walkers alike.

    Certainly, there are many runners with a signficant LLD (over 3 mm) that do not get injured. In addition, I have treated literally hundreds of runners over the past 27+ years with heel lifts or full sole lifts on the short side that has reduced or alleviated their symptoms. In my mind, doing a leg length evaluation should be part of the initial clinical evaluation of all runners with injuries.

    My clinical experience is that LLD will cause asymmetrical symptoms in runners. For example, the runner may have plantar fasciitis on only one foot or iliotibial band syndrome in only one knee. Therefore, when I see asymmetrical symptoms, my clinical suspicion of LLD, or some other asymmetrical foot/lower structural deformity, is increased.

    What I have seen when teaching podiatry students, podiatry residents and podiatrists over the years is that many of them, mistakenly, seem to think that a LLD is one of the few causes of asymmetrical symptoms in runners. For example, they often don't consider asymmetry in STJ axis location, forefoot deformity, transverse plane alignment, tibial or rearfoot frontal plane position, ankle joint dorsiflexion or medial arch height as being a possible cause of asymmetrical symptoms in runners.

    One must also consider asymmetrical running surfaces as a possible cause of asymmetrical running injuries, such as running on a cambered road. In addition, running in shoes with asymmetrical structure, whether the shoe was originally made that way, or was worn into that structure by the runner may also cause asymmetical injury. The experienced sports clinician should consider all these possibilities when treating injured runners.

    Here is a paper I wrote three decades ago that outlines other factors to consider in the history of the runner-patient when trying to determine the cause of their injuries (Kirby KA, Valmassy RL: The runner-patient history: What to ask and why. JAPA, 73:39-43, 1983).
  15. Craig Payne

    Craig Payne Moderator

    I am not denying its a problem, I just struggle to understand how the body knows it got a short or long leg when running as only one foot is in contact with the ground. Surely if the body is to know that it has a LLD, both feet need to be in contact with the ground, and probably side by side.

    I accept the "hump" analogy I mentioned and the "slope" analogy that Eric used, but is that really a sufficient mechanism for the body to detect the difference?
  16. The longer leg and the shorter leg will tend to function asymmetrically since the central nervous system (CNS) is continually monitoring how to optimize metabolic efficiency during running and will, therefore, continually make adjustments in the kinetics and kinematics of gait, in each limb, in order to achieve optimum metabolic efficiency.

    In other words, the CNS doesn't need to "know" it has a LLD. What the CNS does do is attempt to adjust the magnitude, temporal pattern and pattern of efferent muscular activity to the lower extremity muscles (and the rest of the muscles in the body) in order to achieve optimum metabolic efficiency for the whole body during running. Much of the afferent input into the CNS is directly affected by the accelerations and decelerations of the center of mass (CoM) of the body during running for each running step. The CNS likely alters the contact positions of all the major lower extremity joints for each limb in order to minimize accelerations and decelerations of the CoM and, thus, conserve metabolic energy. These changes will directly affect the stiffness for each lower extremity.

    Therefore, I don't believe that the CNS has to consciously recognize that it has a LLD. Rather, when the CNS is changing the function of each lower extremity in an individual with a LLD, the CNS is simley doing its daily job of continually monitoring and changing the kinetics and kinematics of its lower extremities to make the physical task the most metabolically efficient and the most comfortable for the individual.

    Good discussion.:drinks
  17. mr2pod

    mr2pod Active Member

    What about other compensations that the body has already made for the LLD from double limb support activity like standing/walking - which most people do more of than running.
    Is it possible that this may then effect the "symmetry" of the running mechanics.
  18. Paul Bowles

    Paul Bowles Well-Known Member

    You are assuming the LLD is the issue and not the symptom or compensation itself! Opens a can of worms!
  19. Here's a few papers correlating LLD to gait function parameters in walking.

    Here's also an interesting paper on artificially induced LLD in older adults and its effects on muscle activity and metabolic economy of walking gait and a very good review paper on LLD from Gait and Posture.
  20. mr2pod

    mr2pod Active Member

    I was taking Craig's original post that said "structural LLD".
  21. Javier Pascual

    Javier Pascual Active Member

    Hello everybody,

    I would like to add my two cents on this topic. I´m currently running a study in my own office in patients with limb length discrepancy (diagnosed with full limb radiographs in standing). What we measure is foot position via FPI and plantar pressures in standing and walking.

    In my experience, limb length difference can cause asymetrical simptoms and can cause asymetrical foot position in standing wallking and running. In my humble opinion, the "key" of this is the asymetrical load that each feet support in limb length difference. Because spinal compensations, patients with limb length differences can have an increase of load in the shorter limb compared with the longer limb or, conversely, can have an increase of load in the longer limb compared with the shorter limb. I can´t explain why this happens... But is a fact in my patients. In my experience, limbs with higher loads (independently if they are shorter or longer) tend to pronate more and tend to have more symptoms in that limb (unilateral plantar fasciitis, Achilles tendinosis, ileatibial band syndrome, etc...) compared with limbs with less load (again, independently if they are shoter or longer).

    We have only 13 cases (after 1 year and a half and I do not know how long is this going to take) but results seem to confirm this hypotesis at this moment (I don´t know what will happen increasing the subjects).

    Hope this helps,
  22. Keep up the good work, my friend. I look forward to reading your results when the study is finished.
  23. Javi:

    Glad you brought up your study here which you told me about while we were visiting with you in Madrid last month. (Segovia and the Roman Aqueduct, however, was the best!) I think your study will help increase our knowledge and shed some needed light on this controversial and sometimes confusing subject.

    Keep up the good work!:drinks
  24. Perhaps, when you have a larger sample, you could look at the relationship between the size of the limb length discrepancy and the other variables, i.e. you could correlate the magnitude of limb length discrepancy with the other variables- either univariate or muti-variate analysis.
  25. Griff

    Griff Moderator

    Attached Files:

  26. Oh my! That is a photo of Frank Shorter running in "minimalist shoes" 35 years ago! And Chris McDougall and Blaise Dubois want us all to believe that "minimalist shoes" are the latest, greatest type of shoe style and that runners in the past only ran in thick-soled, too-cushioned shoes!

    Is it possible that "minimalist shoes" have been continually worn by runners for the past 35+ years and were previously known as "racing flats" but now, due to people like Chris McDougall and Blaise Dubois, people are wrongly being told that these shoes are the latest, greatest idea in running shoes?!


    If we could only be back in 1977 again when the nutty barefoot/minimalist shoe advocates weren't confusing ignorant runners with their half-baked ideas that some shoe designs are always better than other shoe designs for all runners, that orthotics are bad for runners and that heel-striking is bad for runners. Back then, we just ran in the shoes that worked best for us...then ran a whole lot of miles in them...and were absolutely delighted when shoe companies were starting to give us the option of running in a more cushioned running shoes for some of our training runs!
  27. HansMassage

    HansMassage Active Member

    Adding my small experience. Radiologist runner cam to us for assistance because we had full spine film which was not available where he worked. Put him on a stool so that we could get a view from the plantar surface to the top of the film. found a 6 mm difference in the tibia.
    The interesting finding for this discussion is that the stance was symmetrical from the pelvis down to the distal tibia where the difference was made up by the arch of the foot.
    Alluding to the preceding posts on the effect on the central nervous system, The full foot 6 mm lift from our local orthotist improved how long he was comfortable at work and running.
  28. drsha

    drsha Banned

    What if its not! How would that change the "complete sense of Eric's statement" and the logical progression of his thoughts?

    What if structure plays an important role?

    What if, on the short side, the runner has a foot structure that reduces the plantarflectory stiffness of the 1st ray which causes an increased dorsiflexion stiffness moment to the 2nd and or 2nd and 3rd metatarsal heads that magnifies the pathology of an increased supinatory moment in the rearfoot that applies additional dorsiflectory moments to the lesser mets in this foot?

    This could also be applied to the development of lesser interspace neuromas being more frequently found on the short side or plantar fascitis being found more often on the long side.

    Any sense or logical progression to my thoughts?

    Summarily, IMHO, (see the thread on The Inclined Posture, even small amounts of LLD, both structural and functional should be determined to exist so as to decide if treatment is valuable to inject on a case to case basis. http://www.podiatry-arena.com/podiatry-forum/showthread.php?p=99750#post99750


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