Before reading this, realize it’s lengthy and somewhat detailed. Either get comfy, or come back and read it later. If you’ve ever been told you have “one leg shorter”, this article is for you. If you have a friend who’s been told they have one leg shorter, forward this on to them…
Both in private practice and in working with the Rev3 triathlon series across the country, I treat hundreds of pro and age group triathletes. In doing so, I hear so many stories of anguish and despair as the athletes recount their history of injuries and what they’ve done to try and remedy the problem. This is the part when I get frustrated, because many, if not most of their previous treatments are questionable at best, but downright irresponsible when they tell me what they were prescribed by their health care provider.
I could make this into a small book if I were to get into the cortisone injections, the colorful self adhesive stretchy taping and the over abundance of stretching an injured muscle, but this post will strictly be about a pet peeve of mine – the “one leg is shorter than the other” excuse. (from here on out, I will refer to a Leg Length Inequality as “LLI”)
The post will be in 4 sections:
- How was your LLI determined? (methods are important)
- Is the leg really shorter or, does it just appear that way? (functional vs. anatomic)
- Is your LLI even relevant? (size IS important…)
- What should you do about it? (Can the treatment cause more problems?)
1) Functional vs. Anatomical Differences
Anatomic LLI denotes an actual difference in the length of the femur, tibia, talus or calcaneus, which are the weight bearing bones of the leg. Functional LLI is referencing a difference in the apparent length but is caused by biomechanical issues in the kinetic chain such as pelvic rotation, excessive foot pronation, knee valgus (knee deviating inward), muscle contractures etc. In other words, in a functional LLI, the length of the bones isn’t different side to side, but one foot may be pronated, one knee may be collapsing inward a bit or some other factor that makes one leg “appear” shorter”.
Trying to correct a functional LLI with a shoe insert (heel lift) is silly, and not addressing the real problem. In his book, Michaud correctly states “a heel lift should never be used to treat a functional limb length discrepancy because the lift does not address the cause of the discrepancy and may even create a unilateral weakness of the involved lower extremity” 
2) How was your LLI determined?
If we want to have a discussion on LLI, we have to realize that the way the vast majority of people are diagnosed is by laying on a table and having a clinician look at their legs with a visual inspection. Unfortunately, this is a very unreliable way of looking at things as there are many factors that can cause one leg to “appear” shorter, including pelvic obliquity, suprapelvic hypertonicity (muscle tone in the low back pulling asymmetrically on the pelvis) etc. Many studies have shown that this method is unreliable. For example, Rhodes et al., demonstrated that the side and magnitude of “short legs” were not significantly correlated with radiographic anatomic LLI, indicating they are separate phenomena .
In another study, 45 patients were examined via this method by 2 clinicians. All (100%) of patients were determined to have a leg length discrepancy (Yes, you read that correctly – 100%). Also, there was “poor reliability when determining the precise amount of that leg length difference.” In addition, the study noted “There does not appear to be any correlation between the side of pain noted by the patient and the side of the short leg as observed by the clinicians” 
Many therapists will say that they are more accurate because they measure the leg length by using a tape measure to go from a point on the pelvis to a point on the ankle. Again, this doesn’t account for functional differences between sides. One study summarized this nicely by stating, “Tape measure methods for measuring LLI have been found to be of equivocal accuracy and may be less accurate than radiological criterion standard method for assessing anatomical LLI” 
OK, so doing a visual examination isn’t reliable, using a tape measure isn’t reliable, what’s left? One purportedly reliable method is done with a standing x-ray of the pelvis and measuring the levels of the femoral heads. This method was developed by Friberg and even he states that it is unreliable, “The method described here is not meant to substitute the methods for measuring accurately the length of the different parts of the lower extremity” 
Essentially, it is unreliable because it fails to account for other functional factors. (For example, I take an X-ray of your pelvis so I can see the height of each femoral head. Is there is a difference in the length of the bones, or is it because there is more pronation on one side which is causing that leg to “appear” shorter?)
Another article pointed out that, “methods that incorporate both anatomical and functional LLI without distinction (eg, Friberg method) necessarily overestimate the incidence of anatomical LLI compared with a stricter definition.” 
So what is the stricter definition? The only way to reliably determine an anatomic LLI is to take x-rays of the lower extremities and actually measure the length of the femur, tibia, talus and calcaneus, since these are the primary weight bearing bones. However…even when that is done (usually laying down), it doesn’t account for the other aspects of biomechanics which occur when standing, running or walking. For example, if I have 7mm LLI when x-rayed laying down, maybe I also run with more knee valgus on that side which would negate the anatomic difference. It is an inexact science at best!
3) Is your LLI even relevant?
Let’s pretend that you’re healthcare provider is “positive” there is a LLI. They want you to wear a heel lift to compensate for your 12 mm short leg… Is 12mm (1/2 inch) a lot? Is 6mm (1/4 inch) a lot? what about 19mm (3/4 inch)? Well, we have some clues…
Studies show that 90% of the population has LLI . We know that LLI of >20 mm (>3/4 inch) affects only approx. 1/1000 people. .
So, if LLI is so common, and 999/1000 people don’t have LLI greater than 20mm, how big does LLI have to be before it becomes “clinically relevant”. In other words, how big does LLI have to be before it causes either gait compensations or pain/injury? Again, we have some clues…
Another study, looking at 35 marathon runners, found “discrepancies of 5 to 25 mm are not necessarily a functional detriment to marathon runners, and no consistent benefits could be attributed to the use of a lift.”  Again, another study used data from force plates to look at how compensations for LLI happened. They found a threshold discrepancy of 3.7% of the limb length (approx 20mm on average) before an asymmetrical gait occurred . Yet another study examining gait on 35 children found “discrepancies of less than 3% of the length of the long extremity were not associated with compensatory strategies.” 
So, these studies show that gait compensations usually do not occur in subjects with LLI less than 20mm (3/4 inch), or less than 3% of the limb length. Since 999/1000 people don’t have LLI >20mm, and gait compensations and ground reaction forces aren’t different with anything less than 20 mm, why all the hype? In other words, in a typical triathlon of 3000 people, there are only 3 people with a LLI >20mm. My own anecdotal experience  in my clinic and working on hundreds and hundreds of athletes at triathlons across the country tells me there are a heck of a lot more people than that who have been “told” they have LLI.
4) What should you do about it?
So, we’ve examined the unreliability in determining LLI, we’ve looked at functional vs. anatomic LLI and realized that anything less than 20mm difference should probably be left alone (exceptions exist, such as acquired LLI. For example, people who have a shorter leg due to a femoral fracture).
So now, what do we do if there truly is LLI that needs to be compensated for?
As you may have already guessed, there is even disagreement as to how to deal with the LLI if one is found. In his textbook, Michaud states that placing a heel lift under the calcaneus will result in 33% less of a change in the total compensated height, since the talus is 1/3 of the way between the calcaneus and the metatarsal heads. For example, a 6mm lift under the calcaneus will result in raising the talus 4mm 
In addition, only using a heel lift ends up causing “altered motion and/or transfer weight to the medial forefoot.” Essentially, this then means that your are altering the biomechanical stresses applied to the foot, raising the potential for foot pain/injury by altering it’s normal function. To compensate for this, many clinicians recommend a full-length insole, rather than just a heel lift. I don’t think I need to say it, but I will: this will still result in altered biomechanics of the foot, and again, raise the potential for foot pain and injury.
However, this also brings up another point. If there is pain somewhere, and the LLI excuse is used without properly addressing the real problem, more problems can result. Rather than disclosing names, I can tell you of one pro triathlete this year who played around with inserts after she was told she had one leg longer. She missed most of the season because she was battling pain. At a Rev3 race, she came to see me. It really wasn’t a long diagnostic process to realize that she had an internal hip pathology and needed surgery. She went back home, consulted with a good surgeon who agreed that there was a significant internal hip pathology and she has since had the appropriate surgery. Could the whole thing have been avoided with proper earlier diagnosis? I guess we don’t know, and it’s pretty tough to speculate.
My point is, messing around with invalid and unreliable diagnoses delays proper treatment on the real problem.
Please keep in mind, this article is not intended to deny that LLI exists, doesn’t cause pain and suffering, or should never be treated. My problem is that it is over-diagnosed without proper thought or investigation, not diagnosed properly and usually managed poorly. Until healthcare providers actually take the time to THINK and critically analyze runners in a thorough and step by step process, quick and easy solutions will prevail…such as cortisone injections, stretchy colorful taping and heel lifts.
*** As of Aug, 2015, I will be unable to respond to any of the questions asked in the comments section of this post – I appreciate all the questions, but with the medicolegal system the way it is today, advising people over the internet is a dangerous business and one that I would like to steer clear of. Please consult with your own physician, chiropractor or physical therapist with whom you have an established doctor/patient relationship with.
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13) Ha! Just checking to see if anyone is looking at the references. Good for you!
14) Michaud, Thomas, DC. Human Locomotion: The Conservative Management of Gait-Related Disorders. Newton, Massachusetts: Newton Biomechanics. 2011. Pg. 188