The long and short of… Leg Length Differences

At least once a day I hear or see a therapist discussing leg length discrepancy (LLD) or to give it it’s technical term ‘Anisomelia’. I hear therapists often explaining how LLD is a cause of pain and blame it for a whole host of movement dysfunctions and muscle imbalances, and then go on to use various treatments to correct it.

I question LLD. I question why it gets blamed so often, I question how it’s assessed, but more importantly I question does it actually cause any significant adverse biomechancial dysfunctions so often in so many.

What is LLD?

There are two classifications of LLD, Functional, sometimes referred to as ‘apparent ‘ and Anatomical, sometimes referred to as a ‘true.

Anatomical or true leg-length discrepancies are when there are actual measurable skeletal differences in the shape and length of the leg bones, such as the femur, tibia and fibula. They can also include deformities of the foot and ankle bones, as well as the pelvis.

These bony differences are further subdivided into two categories; those that shorten a limb and those that lengthen it. 

Congenital growth deficiencies, bone or joint infections, growth plate fractures or dysfunctions, among other things can cause lower limb shortening. Causes of lower limb lengthening are rarer and are caused by conditions such as hemihypertrophy.

Functional or apparent leg length discrepancies are where there are no bony differences and the legs are technically the same length, instead its other conditions such as spinal scoliosis or pelvic asymmetries that create the appearance of one leg to be longer or shorter than the other.

Other causes for apparent leg length discrepancies are believed to be from so called ‘excessive’ ankle pronation, knee genu varum or valgum, or even possibly due to soft tissue contractures or imbalances.

How to identify and measure LLD?

There are many methods to measure LLD, some more reliable and validated than others. The gold standard is radiographically, with techniques called scanograms or orthoroentogenograms, these are a series of three X-rays taken in succession of the hip, knee and ankle joints, the bones can then be measured accurately. However, other imaging techniques such as CT scans and MRIs are also found to be useful in measuring LLD (source).

However, these tests aren’t infallabe and more importantly they at not available to therapists in clinics. They are expensive and of course have radiation issues to consider.

So other clinical tests have to be used by therapists. The most commonly used method is by measuring the distance between bony landmarks, normally between the ASIS and the medial malleolus. However using this method does have issues. First is accurate location of the bony landmarks can be difficult in some of our ‘adipose rich‘ patients, and muscle girth differences can skew measurements as the tape runs down the leg.

Alternative methods of measuring from the umbilicus or even the xiphisterum have been suggested and some suggest that there is also a need to measure to the bottom of the heel so that any discrepancy in the ankle joint is included.

So what’s the reliability and accuracy of these tape measure methods? Well Woodfield found moderate reliability (58%) between two examiners within 1/8th of an inch difference (that’s 3.2mm to us metric users) and excellent reliability (92%) within 3/8th of an inch (roughly 1cm). Jamaluddin also found that tape measurements between the ASIS and medial malleolus between two trained assessors is reliable to within 5mm when compared to the gold standard CT scanogram measurements, as does this recent study. So tape measurements can be considered as actually pretty good at detecting leg length differences bigger 1cm, but not so good under this.

Other clinical tests used to check for LLD are simple observational tests of the ASIS and PSIS bony landmarks to assess if there is any anterior or posterior rotation of the pelvis. 

Recently some instruments called digital inclinometers have been claimed to be more reliable and acurate to measure these angles, however there currently no evidence of this claim.

However, even if you are using simple observational measurements or fancy digital inclinometers, the reliability of all these pelvic position tests is highly questionable (source). 

As I’ve discussed before in my SIJ posts, the normal variation in pelvic skeletal morphology makes tests that use bony landmarks completely invalid and useless. 

The position and heights of the ASIS and PSIS vary normally up to 23° with no robust correlation ever been found between increased or decreased angles and injury or pain in any conditions.

So how anyone can determine if an ASIS is lower or higher than it should be due to a so called ‘misalignment’ or ‘torsion’ is beyond me and the evidence, it’s merely guess work.

Another observational clinical test commonly used for LLD is where the patient is asked to lie supine, and perform a couple of bridging movements with their legs together, and knees bent at 90 degrees. 

An ‘eye ball’ check of the height of the top of the knees is taken to see if there is any difference in femoral length, and then the legs are extended and again another ‘eye ball’ scan is used to check the alignment of the medial malleoli to ascertain if any there is any tibial length differences. However yet again as this is only an observational test it’s accuracy is limited to either a ‘yes or no’.

How common are LLD?

That’s simple, they are common, very common, very, very common.

In fact nealy all of us (up to 95%) have a LLD to some lesser or greater degree (source) with the average difference for most being approx 5mm, with the right leg being most commonly the shorter than the left (source)

The more important question to ask is when does a leg length discrepancy become a significant and potential factor to consider in someone’s pain and pathology?

This is a lot harder, if not impossible to answer at times.

When and why does LLD cause issues?

When does LLD become significant isn’t truly clear, but the general consensus in most literature and by most clinicians is that anything over 1cm is probably worth considering (source)

However, the key word here is ‘considering’ not automatically blamed. Other factors such as the ability of the body and kinetic chain to compensate for the inequality have to be considered. How this is done, is even more unclear, and from my experience and observations of other therapists who ‘do’ this it tends to go on nothing more than their ‘intuition’.

The mechanisms often explained as to why LLD causes pain and pathology is varied and sometimes complex.

To keep it simple most are thought to occur through excessive ground reaction forces, mainly in the shorter limb as it has further to travel to reach the ground (source). 

These ‘excessive’ forces have to be absorbed into the kinetic chain and it is thought that they can adversely stress and strain joints, muscles and ligaments of the lower limb, pelvis, and lumbar spine. In fact some blame LLD for pains felt as far as the jaw TMJ, which I think is pushing the boundaries of interregional dependance and plausibility a little too far!

Anyway, these excessive forces are thought to lead too and create pathology such as OA, tendinopathies, back pain etc. 

However just to confuse matters, other studies show a correlation with pathogies in the longer limb with LLD such as stress fractures and planta fasciitis.

Either way, there are many papers that may show a correlation between LLD and pains in certain populations in certain areas. For example this large prospective trail on over 3000 patients shows those with a LLD of more than 1cm may have a greater prevelance of knee joint osteoarthritis. 

But conversely, there are also many papers that show no correlation between LLD and common musculoskeletal conditions such as this paper on lateral hip pain and this paper on chronic low back pain.

As always in research is important to remember that a correlation does NOT automatically imply a causation.

As with most things in the evidence base, I am sure if we looked hard enough, digged deep enough, and ran enough data through some clever statistical skulduggery we could find that LLD is correlated with most things, or conversely that it isn’t!

Too quickly and too often blamed?

In my opinion LLD is a nice, easy, and convenient scapegoat for many therapists to blame as a cause or source of pain, often with most of those blaming LLD not really taking into account that humans are asymmetrical and the remarkable and amazing capacity for us to adapt to asymmetry.

This ability to adapt to asymmetry is neatly emphasised by this study which induced a LLD, up to 3cm, and measured joint kinematics and forces and found no significant differences between limbs.

In my opinion therapists who rush to blame a LLD as a problem usually have a vested interest in doing so, normally a sales opportunity for some fancy gadget or gizmo designed to identify or correct the ‘wonkyness’.

However, some therapists simply have misinterpreted or cherry picked the research to support the notion of leg length differences, and some just don’t have a good enough understanding of the other factors that influence biomechanics and of course can produce pain. 

Some therapists have also been lead astray having been taught the assessments and treatments of LLD by a charismatic or influential ‘guru’ again usually with a vested interest in finding LLD.

Simply put, blaming LLD for a lot of patients pain presentations and issues just doesn’t make any rationale sense to me, nor does it fit with any sound clinical reasoning. 

For example it’s not as if people wake up one morning, falling over as they get out of bed because one of their legs suddenly became shorter over night, LLD doesn’t happen quickly, most of the time, unless it’s been created traumatically or surgically as in after a hip replacements, most LLD are congenital.

The traumatic causes of LLD are a different ‘kettle of fish’ and yes they may indeed need correcting for some. But most LLD don’t happen suddenly, they happen gradually, over time, over a long time, and so the body slowly and quietly adjusts and adapts.

So a therapist who suddenly finds a LLD in a patient one Wednesday afternoon, that’s been with the patient all their life, and blames it as the cause of their back, knee, hip pain just doesn’t make any sense to me.

The simpler explanation?

The inconvenient truth for those that blame LLD is that are far more simple, rational and evidence based reasons for most common pains and problems that patients come to see us for, such as joint or tissue overload.

However it is these simple diagnosis that I find that many therapists do not want to give, or feel uncomfortable giving to patients. Many therapists feel that they have to justify and demonstrate their ‘skill’ and training by spotting and identifying subtle biomechanical abnormalities such as a LLD. 

This they think gives an appearance of skill to their patients, demonstrating that they have found a plausible scientifically sounding diagnosis, and so reassures the patient that they are dealing with a true professional.

Now, before I sound like I am trashing all therapists again and tarring them all with the same brush, and completely rubbishing and ignoring LLD, I’m not.

I do accept that a LLD may amplify and contribute to certain overload problems, in certain conditions for some people, and I do check for LLD in some instances, and if I do find one greater than 1cm I will see if correct it, with a simple off the shelf insole or heel lift, reduces the sensations of pain or discomfort, just like a symptoms modification test.

If it helps great they keep the insole or heel raise in but usually only temporarily to see if it reduces pain and keeps them moving. I then get most to wean off any device and begin the most important part of the rehab, a progressive strengthening and loading of the joint and tissues to restore is capacity to withstand the stresses and strains of the movement or task it couldn’t do before it started to breakdown and hurt.

So in summary leg length differences are common, and finding them is easy! Very easy! However, deciding if they are a factor that is contributing to pain and if they need correcting is not so easy.

In my opinion leg length differences are mostly NOT a primary issue and many don’t need correcting. Our bodies have an amazing ability to adapt, and in most cases have already adapted to any leg length differences we may find, and if they haven’t, they can, and will do, given the opportunity!

As always thanks for reading!

Happy ‘wonky’ exercising

Adam

 

 

20 thoughts on “The long and short of… Leg Length Differences

  1. I’m really glad I have found this information. Nowadays bloggers publish just about gossips and web and this is actually irritating. A good web site with exciting content about physio, that’s what I need. Thank you for keeping this web-site, I’ll be visiting it.

  2. I would agree that the accurate assessment of leg length is extremely difficult particularly in the clinical environment. Even the gold standard of a CT scanogram has a degree of subjectivity as to whom and where the measurement markers are placed. I have measured some of these myself and usually take a group of measures to try and get a consensus. The varying clinical assessments are all prone to error and each practitioner should develop a consistent assessment technique but not rely on one measure for diagnosis.

    The degree of discrepancy relevant to injury is often quoted fairly high in the literature for exactly this reason; it is difficult to be precise with the assessment but, if you measure 1cm for instance it is likely to be present.

    However, the actual relevance is much more dependent upon a range of factors, not least how well the individual has adapted to the imbalance and their activity levels etc. as you state. I would entirely agree that an alteration to training could spark the problem but, by the same token, there can be a threshold of activity (a set distance for instance) beyond which the degree of discrepancy causes enough dysfunction to lead to injury. I would also proffer that this threshold reduces with age (eventually) which is why a problem may only manifest in later years.

    I assess LLD in a high percentage of my patients (accepting that this is a clinical assessment and will have error) and would estimate that less than 50% of these have any discernible LLD. Not scientific I accept but certainly not as high as 95% and I treat a pathological sample group.

    I would agree that LLD can be a scapegoat but it has to be considered as part of the overall diagnosis and management plan either for the short or long term. The secret of any functional / biomechanical assessment is to determine how much of the pathology is due to alignment (foot / leg / pelvis etc.), muscle strength / flexibility, neuromotor control / training patterns etc. If someone has had a one off issue and it is linked to control and training, that is clearly the target. However, if someone is having repeated asymmetrical injury patterns, LLD may be more relevant. If it is felt that the foot function is contributing to injury, then LLD has to be considered as altering foot function will alter the way the body adapts for the LLD.

    Our approach to assessing all of our cases is to determine what we feel are the key factors inhibiting / altering function and then to target these / refer accordingly. As podiatrists that means do we feel it is structurally related and requires control, due to neuromuscular control or training patterns with appropriate referral or a combination. We can then determine if any control needs to be for the short term or long term.

    In order to assess the clinical effect of LLD, we perform inshoe pressure analysis to look at symmetry. Rather than looking at absolute pressures / integrals etc., we evaluate symmetry of heel loading / force time curves and centre of pressure lines and then revaluate with LLD control.
    I have posted some examples on my Facebook page (https://www.facebook.com/PremierPodiatryLimited)which show:

    • A professional athlete with LLD but sufficient strength and control to function without any detrimental effect.
    • Someone walking who has asymmetrical force / time curves without but symmetry with control
    • Someone running who has symmetrical Centre of pressure lines without and symmetry with LLD control.

    I fully accept that much more research is required in this field but at the moment, this at least allows us to have an idea of the effect of discrepancy and control.
    With the introduction of our 3d gait analysis system, we have just started looking at the effects on more general function but it is too soon to comment but exciting.

    I agree entirely that orthoses are not required to control for LLD alone. In the majority of instance I will either provide a heel raise, a whole shoe insole (both of these are peanuts and I include as part of the consultation fee) or advise a shoe modification. If we wish to control foot function, then we will provide orthoses but also the appropriate level of LLD control.

    So, in summary, I agree that the assessment is fraught with error (a point I advise my patients) but personally give it more relevance than yourself. I do not get hung up on the degree of discrepancy, more the effect on the individual within the framework of their presenting history and the likely benefit of control whether the control I is simply for the LLD or as part of controlling foot function in general. Here we are in agreement; spotting the discrepancy is one thing, determining the relevance is another.

    • Hi Trevor

      First and foremost can I say thank you for your time and very valuable and valid comments.

      I agree with nearly all that you say here and I know that it comes across as I’m bashing LLD and insoles etc,and I am a bit as I do get exasperated with many therapists focusing on this and not the bigger issues. As I say I do accept LLD has a role in pathology and pains, but I still argue that give time and correct loading the body can and does adapt without the need of corrective devises, the issue is many patients dont want to or cannot afford to give the body the time it needs or they simply cannot be bothered to do the hard work!

      Anyway once again thanks for your valued opinion

      Kind regards

      Adam

    • Hi but what if you broke your leg and now have a leg 6mm shorter and no constant back pain. Will it get worse as get older or will your body adapt

  3. Thanks Adam, that was a great review of LLD and measurement. Certainly nothing there that hasn’t been said before, but it certainly something that needs saying!

  4. I found that article a very interesting read. Thank you for taking the time to write it and I look forward to more posts in the future.

  5. Thanks for a great article. I like how you don’t oversell yourself. I find the most useless people are the ones who won’t listen, think too much of themselves, and think they know everything. Anyway. I’m pretty sure I have this LLD. I’ve had it probably most of my life, as far as I can remember. I’ve seen some of “the best doctors in the world”, none of which picked it up, but the more study I do, the more I realize its whats been bothering my hips, hams, groins, and sijoint. I still don’t have the scans to prove the problem. I was hoping you could shed some more light on the types of scans available, and if they can be found in Canada, because I’ve had over 50 appts and the best I can get is a standing xray of my pelvis.

  6. Hi Adam,
    I have to agree with your point that LLD is not always the main problem when a patient presents with pain, however I have to disagree with your being ok with the way the body adapts to these leg length differences. As a physiotherapist and someone who has a functional LLD >1cm I have enjoyed studying the correlation to my own PFJ,SIJ and neck pain related to the imbalances that result from my own LLD. My right sided foot overpronation and internal rotation of my tibia/femur and anterior tilt has lead to my reoccurring PFJ pain. I can manage it with ITB rolling but this isn’t addressing one of the main contributors I feel which is my leg length difference. Leg length differences I believe can be one of the main driving forces for chronic pain.

    Regarding your statement that ” blaming LLD for a lot of patients pain presentations and issues just doesn’t make any rationale sense to me” I believe being a responsible therapist particularly with patients with reoccurring injuries/ patterns of pain or chronic pain In relation to my patients I feel it’s in my patient’s interest to address not just the local issue but to bringing attention to the imbalances stemming from foot/ankle and hip. I believe in LLD and those that are active the imbalances and the ‘adaptions’ higher up that are evident with LLD contribute significantly to reoccurring pain. Rather than call it “intuition”, I call it logic. Force not distributed evenly has the ability to cause excessive wear and tear and therefore pain etc. In the case of PFJ pain The TFL is more overactive on my shorter side, where I pronate and have more anterior tilt. Therefore the more I run this LLD is going to be causing my ITB to be tighter on my right side and my patellar to maltrack. Yes I address the localised issue of ITB tension, encourage VMO activation and use Mcconnell taping to reduce symptoms… but this is a short term solution. The shorter leg I believe is important to address the pronating foot with potential orthotics and to address the inhibition of gluteal muscles that could additionally have induced the pronation. Without looking at these main drivers it’s just going to lead to frequent relapse of the condition. Addressing this is also having the goal of reducing the continual overload on joints that over time would more likely lead to patellarfemoral pain becoming chondromalacia, tendonitis becoming tendinosis, disc pain becoming a disc bulge.

    I feel that your opinion on therapists who educate and bring LLD to the patient’s attention and insist on improving this to improve the patients condition are using LLD as a ‘scapegoat’ actually couldn’t be further from the truth. Therapists who treat the smoke and not the fire are more likely to guarantee returning business with the same reoccurring problems. It’s important to address the localised problem but physiotherapists are encouraged also to look at contributing factors? I know as a therapist if someone comes to me with chronic lower back pain and they have a leg length difference that is functional and an adaptive scoliosis, by treating the joints effected and looking at improving activation of inhibited muscles and stretching of muscles that are overactive +/- orthotics/heel raise will be ensuring my patient has long term less chance of future exacerbations but additionally less excessive force on joints in their spine and therefore a reduced rate of wear and tear.

    Lastly physiotherapists are the gurus of the musculoskeletal system and I think there is no problem in owning that in biomechanical assessment and management. It saddens me when patients report to me previous physiotherapists they’ve seen who have just used passive treatment like ultrasound or TENS only and provided some basic stretches without utilizing the skillset to investigate and address the biomechanical contributors and educating and tailoring a program specific to their patients.

    A good physiotherapist will look at the patient as a whole and address leg length discrepancy as best possible. It is not oversell, it’s justified good patient care in my opinion.

    • Hi Danielle

      There are so many points I wish to debate with you in your comment I don’t know where to start, and I really haven’t got time.

      I will just say that yes biomechanics are important to consider of course, but we are all guilty of over assessing and making rash and misdirected assumptions based on some sketchy evidence and peer opinion and beliefs that get handed down and ingrained.

      We must consider the body as a diverse and adaptable ecosystem not like a car or a machine, we are biological with a wonderful advanced and crazily complex neural system, regulating it all, this is what we should focus on more, not the leg difference of pelvic asymmetry which is mostly not relevant

      Regards

      Adam

  7. HI Adam,
    I broke my leg when I was 10 months old and now 35, after two children I am experiencing a lot of pain on my longer side. Foot ankle, achilles, calf, knee, thigh, hip and lower back. I believe my discrepancy is approx 3 cm due to my femur being differing lengths. Any advice… i’m looking into seeing orthopaedic surgeon and podiatrist for advice. I also am starting clinical pilates one to one helping me to gain strength but I am not understand how anything can help me given the level of discomfort I am in daily as soon as I start moving. I am hoping you can direct me as it’s tricky running after two little boys, and I’m an athletic person otherwise!
    Thanks
    Amy (UK)

  8. I’m confused why would a tape measure be used to measure leg length and not a more appropriate instrument such as an anthropometer/long sliding calipet, or a segmometer?

  9. Sorry. As someone with a true lld I disagree. You think it’s better for the body to adjust to lld rather than a heel lift. In my case – and I assume many others – I developed scoliosis as a result. So addressing this early enough with a heel lift would have prevented this.

    • Im sorry to say there is NO evidence that leg length differences cause or contribute significantly scoliosis, or that a heel wedge would have prevented one from developing.

      Many people with scoliosis have NO leg length differences and also think about the amount of time you are not standing or walking throughout your life, this time will out weigh time on your feet.

  10. have to agree with amplewor. left leg longer, pushes left hip out, causes pain in left hip, and eventual shifting of spine to S shape. Right shoulder below left. It’s common sense really. And your logic Adam is weak. Just because some scoliosis patients have no leg length difference is completely irrelevant. Smoking causes cancer, but there are lung cancer patients that don’t smoke.

    In my case, 1.5cm difference, I didn’t notice until early 30s. Insoles have saved me.

    • Why would a longer leg that you have had all your life now start to push your hip out? And insoles havent saved you, they have given you a belief that they have helped which you have accepted.

      Cheers

      Adam

  11. I am a physiotherapist working in a private practice in Melbourne. I often have patients spontaneously tell me (as part of their medical history along with major surgeries/injuries) that they have one leg longer than the other and that they were informed of this during previous consultation with a chiropractor, osteopath or physiotherapist.

    I can see that this usually stays firm in the mind of a patient as it conjures up dramatic images of deformity and can provide them with a “aha!” moment and a convenient hook to hang all of their physical problems on. It also has the effect of making the therapist seem like a genius to a patient because they are taking a “holistic” approach by investigating something that can, at surface level, seem like a deep underlying cause which has never been investigated before! This makes the therapist and the patient feel quite good during that consultation (which is probably why patients and therapists develop strong emotional attachment to this idea). It also sets up quite a convincing premise for a powerful placebo effect- your leg is short and this insert will make it the correct length again! Problem solved! Now you can stop worrying! (see also- your back is out of place, let me crack that back in for you).

    I am not saying that people wont see some improvement from this approach (we all know how powerful the placebo effect is) but given the available evidence, I doubt this improvement is coming from biomechanical factors. It also has the dangerous effect of reinforcing a body image of deformity and pathology in the patient that they will likely carry with them the rest of their lives (“ah my backs sore, must be my bloody short leg that’s causing it again!”). I feel that in the long term it would be much more beneficial to a patient to reinforce the idea that the body does not need to be mm perfect and that it is a self-modifying machine built to adapt.

    You can then fix a problem by addressing strength and range of motion issues, load management, weight loss, etc. while all the while promoting positive body image and independence. That would be the true holistic approach.

    Disclaimer- Obviously huge leg length discrepancies (getting up to 5cm) caused by trauma or congenital defects need to be addressed. This post is about the small ones in general population that are pathologized unnecessarily.

  12. You sound like your mind is all made up! Obviously, you don’t suffer from true LLD and have decided to portay those of us who do as some kind of freaks. Sorry I wasted my time reading your entire blog… Obviously, you don’t know what you’re talking about.

    • Hi Sylvia, I am not sure what makes you think or say that I portray those with LLD as freaks… thats just nonsense. If you read the blog you will have seen that I say LLD occur in many many people but they dont cause pain or disability in many many people.

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