06 Sep Does leg length discrepancy effect my running?
I thought this weekend I would do a dive into the research around leg length discrepancy and see if we can clear the air in relation to running. Personally, I haven’t focused on leg length discrepancy when working on my running clients but I have found some very interesting findings when it comes to the assessment, injury risk and prevalence of this population. I am curious to know your thought or experiences when it comes to this topic, the running community so far has been very engaged with the blog so keep it coming!
I came across a study titled ‘Methods for Assessing Leg Length Discrepancy. Sabharwal, S. et al, 2008’ and they conducted a level IV diagnostic study and concluded that without scans, taking the average of 2 measurements between your hip bone (ASIS) & ankle (medial malleolus) seems to be the most reliable. If you want to go down the path of scans a CT scanogram was the most recommended when considering accuracy, cost and radiation exposure.
But do you even need to assess leg length? Does it effect your running? A very nice review titled ‘Anatomic and functional leg-length inequality. Knutson, G. et al, 2005’ complied a heap of studies and suggested that a leg length discrepancy less than 20mm is not likely to cause symptoms that require treatment. Reflecting on this, 20mm is quite a large range and will be quite visible to the naked eye. This may be relieving for some runners because it can automatically disqualify a massive part of the population who suspect a leg length discrepancy as the root cause of their symptoms.
If your doctor or practitioner advises that you have a leg length discrepancy then congratulations, you share this ‘abnormality’ with 90% of the population. The same study above found the average discrepancy was 5.2mm. Since the study suggested that 20mm could mean the potential for intervention, I thought it would also be a good idea to see the likelihood of this level of severity. Compiling all the studies in the review (including one that had a population size of 2.68 million) they found that 1 in 1000 had a leg length discrepancy of 20mm or more.
This would make sense from what we know about the body adapting to it’s own circumstances. We know that small biomechanical differences from right side to left side doesn’t lead to injury. The body does an amazing job at adapting to a wide range of different running styles providing that the increase in load is gradual enough to allow adaptation. If small biomechanics were acutely changed because of pain, change in shoes, one-sided orthotics etc, then this would obviously increase the likelihood of injury. Knowing what I know now about leg length discrepancy, I think we can rest a little easier.