I must see a social media post or some other discussion about leg length differences at least once a day. And I hear healthcare professionals saying how it’s a common cause of both pain and pathology, blamming it for a host of movement dysfunctions and muscle imbalances.
Well, I question this and the relevance of leg length differences as a common cause of pain or disability a lot. I also question how leg length differences are assessed and treated and if they need to be at all.
What Is A Leg Length Difference?
There are two main classifications of leg length difference, or as its technically called ‘Anisomelia’. One is called functional or ‘apparent‘ leg length difference, the other is called anatomical or ‘true‘ leg length difference.
Anatomical leg-length discrepancies are where there are differences in the shape of the pelvic, leg, ankle, or foot bones due to congenital deformities, disease, trauma, or surgery. These bony differences are further divided into two categories; those that shorten a limb, and those that lengthen it.
Congenital growth deficiencies, bone or joint infections, growth plate fractures, and other traumas can cause lower limb shortening. Causes of lower limb lengthening are much much rarer and often caused by genetic conditions such as hemihypertrophy.
Apparent leg length discrepancies are when there are no significant structural differences of the bones but other conditions such as spinal scoliosis or other asymmetries create one leg to be longer or shorter than the other. Apparent leg length discrepancies are believed to be caused by things such as muscle weaknesses or imbalances causing things like pelvic torsion, foot pronation, knee varus or valgus.
How Do You Identify Leg Length Differences?
There are many methods to assess leg length differences, some more reliable than others. The gold standard is using radiographic imaging, with techniques called orthoroentogenograms, which is not easy to say but a guaranteed scrabble winner! These are a series of X-rays taken in succession of the hip, knee and ankle. Other imaging techniques such as CTs and MRIs are also found to be useful (source).
However, these methods are not infallible but more importantly they at not available to most therapists in day to day clinics. They can also be expensive and of course, have radiation doses to consider. So most leg length differences are assessed by therapists in other ways.
A common clinical test used is the supine bridge test or the Weber-Barstow Manoeuvre. This where the patient is asked to lie supine and perform a bridging movement with their legs together and knees bent at 90 degrees. An ‘eyeball’ check of the height of the top of the knees is then taken to see if there is any difference in pelvis (A) and the femurs (B) length by looking down from above, and then the tibias (C) by looking from the front.
However, this test doesn’t do well in its clinical reliability with a recent study finding the levels of inter-rater agreement reaching only moderate levels. A more reliable method is by measuring the distance between the bony landmarks of the pelvis and ankle with a tape measure. However, this still has issues with the location of these landmarks being challenging to find in some subjects, and leg muscle girth differences sometimes affecting the measurements.
An alternative method of measuring from the umbilicus or even the xiphisternum have been suggested and some suggest that the measurement is taken to the bottom of the heel so that any discrepancy in the ankle joint is also included.
Woodfield et al (2011) found assessors had moderate reliability with this method within 1/8th of an inch (that’s 3.2mm to us metric users) but excellent reliability within 3/8ths of an inch (or roughly 1cm). Jamaluddin et al (2011) also found tape measurements were accurate to within around 5mm when compared against radiographic images as does a more recent by Neelly et al (2013).
Other clinical tests used to check for leg length differences are checking the heights and angles between the pelvic bony landmarks of the ASIS and PSIS. Recently Digital Pelvic Inclinometers have been claimed to increase the accuracy and reliability of these tests (ref). However, on closer inspection we can see that this isn’t the case, with assessors often finding large differences of up to 10° even when measuring the same subjects on different days. And that’s before we mention the extremely high risk of bias and huge conflicts of interest this study has.
The relevant and useful information you get from all these tests are highly questionable, and as I’ve discussed before in my other posts about the SIJ the natural variation in skeletal morphology makes any test that uses bony landmarks pretty much invalid and useless.
Are Leg Length Differences an Issue?
Leg length differences are common, very common, very, very common. In fact, up to 95% of us are thought to have it (source) with the average being around 5mm with the right leg being most commonly shorter than the left (source). However, the more important question is do these leg length differences cause pain or pathology and if they do how can we tell?
When a leg length difference becomes an issue just isn’t clear at all, but it seems a general consensus in most literature and most clinicians is that anything over 1cm difference is probably worth considering (source). However, the keyword here is ‘consider’ and not panic or jump to hasty conclusions.
When ever someone has any pain or any pathology we have to take into account the many other factors that can contribute to them and not start blaming single sole factors such as leg length differences! We also need to recognise the remarkable ability of the human body to adapt and compensate for all kinds of asymmetries such as a leg length difference.
Many clinicians will blame a leg length difference for creating pain and pathology due to it increasing ground reaction forces in the shorter limb (source) which is thought to adversely over load, stress and strain joints, muscles and ligaments of the leg, pelvis, and lumbar spine. In fact, some even blame leg length differences for dental issues and TMJ issues, which I think is pushing the boundaries of plausibility too far.
Other studies have shown correlations with leg length differences and pathologies in the longer limb such as stress fractures and plantar fasciitis. Either way, there are many papers that blame leg length differences for many pathologies
For example, this large prospective trial on 3000 patients showed those with a leg length difference of more than 1cm have a greater prevalence of knee joint osteoarthritis more often in their longer limb. But, there are also papers that show no correlation between leg length differences and pathologies such as this on lateral hip pain and this on spinal scoliosis.
As always its important to remember that a correlation does NOT imply causation, and as with most things, I’m sure if we look hard enough and tortured the data long enough we could find that leg length difference is correlated with male pattern balding, bad driving, and a dislike of the colour purple .
Too Quickly And Easily Blamed?
In my opinion, leg length differences are a nice, easy, and convenient scapegoat for many clinicians to blame as a cause or source of their patient’s pain. This is because it’s often far easier to focus on these simple biomechanical suspects than look for the far more messy, complex, and difficult factors that can be contributing to their pain and pathology.
Also, it’s far easier to think that humans need to be symmetrical and perfectly aligned like some robot than recognise that humans are complex, messy, wonky, wobbly asymmetrical bags of bones, viscera, and soft tissues that have a remarkable and amazing capacity to adapt and tolerate things.
This ability for us humans to adapt to asymmetries is beautifully demonstrated in this neat little study in which they created leg length differences of up to 3cm in subjects with the use of built up shoes and measured their joint kinematics and forces when walking and found no significant differences as the subjects self-organised around their new biomechanical alteration.
However, large and sudden changes in leg length difference may be an issue for some and may need some management. For example, I see some patients after hip replacements with a sudden significant leg length difference after the operation that has caused some patients to experience new episodes of back and other pains. However, this could also be due to the fact that they are also now more mobile and active after the operation and have increased their activity levels significantly.
Treating Leg Length Differences
Many clinicians also treat leg length differences with many dubious things. Things such as ridiculous manual therapy techniques believed to reset pelvic misalignments, reduce overactive muscles, or release tight fascia causing fictitious postural imbalances and other pseudo-scientific claptrap.
Many do this I think because they feel that they have to justify their existence and fees and in an effort to demonstrate how skilled and knowledgeable they are. This gives them an appearance of expertise and competence to their patients which perversely helps them feel better with the silly treatments they get.
My advice is if you do suspect a leg length difference is a factor in your pain or issues then just try a simple inexpensive heel raise or insole in your shoes for a short while to see if it helps. If it does great use it to help calm down and reduce your issues. But once settled slowly see if you can wean yourself off it and see if your body can adapt slowly around your leg length difference, because you dont want to or may not be able to always wear a heel lift or insole!
Summary
- Leg length differences are common, very common
- Assessing leg length differences clinically is tricky and unreliable
- Determining if a leg length difference is a factor or not in pain or pathology is even trickier and more unreliable!
- Many leg length differences are NOT a significant factor and even less need correcting.
- We all have an amazing ability to adapt and tolerate asymmetry, and in most cases already have.
As always thanks for reading
Adam