Leg length discrepancy (LLD) is a measurement that is taken by many rehabilitation professionals when patients present with various conditions. Its something that a lot of people locally to myself present with as a previous diagnosis, their symptoms ranging from plantar fasciitis to headaches. However, I think its fair to critically appraise the research, and ask ourselves if these inequalities are truly associated with all these symptoms and, if so, how much of a discrepancy must exist before we see problems?
Firstly, here are a couple of classifications of LLDs
Anatomical or true leg-length discrepancies (which I think of as “mechanical” difference) are when there are actual measurable skeletal differences in the shape and length of the leg bones, such as the femur, tibia and fibula. These can only truly be confirmed by scanning.
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, pelvic asymmetries or muscular imbalances that create the appearance of one leg to act longer or shorter than the other.
There are numerous ways to measure leg length; and unfortunately, they are all pretty unreliable if the LLD is less than 1cm. (Ref 1). And according to the review study below (Ref 2), which examined studies on LLD over a 25 year period, LLD was found to exist in 90% of the population. In fact, on average most of us have a LLD of 5.2 mm (0.5cm) and suffer no negative consequences.
Reading on, seven studies in the review compared asymptomatic (no pain) individuals with people who had symptoms somewhere in the kinetic chain (knee, hip, and low back) and found that there was no statistically significant difference in leg length (5.1 mm versus 5.2 mm). These results suggest that average LLD is not correlated with painful lower limb issues, the most proximal position to the any fitted orthotic, for example….
Which leads us onto orthoses; again, I come across a huge number of people who have been fitted orthotics, for a wide range of symptoms, and have had them in their shoes for a number of years. Orthotics, also called orthoses, are devices that are worn to “correct” foot and ankle problems without surgery. Most people think of shoe inserts or “arch supports” when they hear the word orthotics, but they can include devices such as foot pads, shoe inserts, ankle braces and similar items. They should – in my humble opinion – only ever be fitted by a trained podiatrist. I am a huge fan of the work of Ian Griffiths, Sports Podiatrist who says “Orthoses are rarely, or seldom, going to be a life sentence….Orthoses change the load in our tissues; rather than thinking of Orthoses as an external crutch, or brace, which they are not; as something which realigns the skeleton, which they don’t…they are another way of managing load…When that tissue is built up to have the appropriate and the requisite strength, conditioning, endurance capacity; that Orthoses is now redundant and should be removed ” (Ref 3)
So, when might a LLD matter? Well, it appears that a LLD of >20 mm (2cm) may be associated with the development of knee osteoarthritis and/or low back pain. A LLD <20 mm can usually be compensated for by passive structural changes.
So, are your legs the same length? Probably not.
Is that the cause of your pains? Probably not
As always, when in doubt, seek out a trained therapist.
- Interexaminer reliability of supine leg checks for discriminating leg-length inequality. https://www.ncbi.nlm.nih.gov/pubmed/21621725
- Knutson GA. Anatomic and functional leg-length inequality: A review and recommendation for clinical decision-making. Chiropr Osteopat. 2005.”