In summary leg length differences are:
- very common, 90% of the population have them.
- hard to accurately assess in a clinic if less than 1cm.
- May be more relevant in growing children than adults.
- Are unlikely to be an issue if less than 1cm.
- However they are also worth acknowledging just in case they play a role.
Its not uncommon to hear people come to the clinic and tell us that they have 1 leg longer than the other and that’s the reason why they have back pain , knee pain , headaches , etc . Is this really the case and does it matter ?
“Only 10% of the population have equal lower limb lengths”
Whats does the science tell us about leg length differences ?
In this paper (Gordon and Davis 2019) which they showed that only 10% of the population had equal leg lengths meaning that the other 90% of people have a leg length discrepancy of up to 1cm.
Looking into this further Knutson (2005) reported that the average leg length difference was 5.2 mm They went on to say that for most people leg difference doesn’t become clinically significant until it reaches approximately 2cm.
A more recent paper (Vogt et al. 2020) gives a nice overview of the topic including these 5 top takeaways on leg length differences. As you can see there are alot of maybes and mights asopposed to definates.
- It’s hard to accurately measure leg length in a clinical setting and detect differences of less than 1cm.
- There may be a link between a leg leg difference of more than 1cm and knee osteoarthritis but was not found to be a factor that may lead to the development of back pain in a number of studies.
- Leg length difference has a greater effect on double-leg stance activities (e.g. prolonged standing). The effect of LLD in single-leg stance activities is lessened as the gluteal muscles are able to stabilise the pelvis. So it may not have an impact on running.
- There is a lack of evidence to support the decision of when to initiate treatment and it shouldn’t be based solely on the size of the discrepency.
- Leg length differences may be significant in growing children compared to adults who have reached skeletal maturity.
Leg length difference and running
Running is less likely to be influenced by leg length differences due to the fact that its a single leg stance activity that rapidly changes from one leg to another. Research has shown that leg-length inequality is not associated with running injuries, the exception to this is that differences of greater than 1.5 cm have an increased likelihood of developing a lower leg injury (shin/calf).
So when should we consider leg length differences ?
I think this table is an excellent synopsis on how we should look at leg length differences
My thoughts on leg length differences
Like many things in patient care, this topic is very nuanced and really comes down to ” it depends” . We can’t dismiss it altogether as irrelevant for all as it may make a positive change in someones symptoms. That’s why we look at it when we are assessing lower limb injuries and even back related problems. It may not be top of this list in why you have your symptoms and may be more of a 1% issue.
Another issue to consider is the body is incredibly capable at adapting to change and leg length is probably one of these skeletal asymmetries that we adapt and integrate quite comfortably into how we move. Think about the amazing amputee paralympians, those athletes show how well we can adapt and overcome the biggest of leg length discrepancies.
I often find that leg length is too quickly blamed for someones issue and if 90% of us have leg length differences wouldn’t we all have issues ?
As always if you are in doubt get it checked out.