Leg length discrepancy and injury

Does Having One Leg Longer Make You More Likely to Get Injured?

We often see patients who have been told they have “one leg longer than the other.”

Understandably, this can lead to a lot of questions:

• Is this why I’m injured?

• Do I need a heel lift?

• Is my running or walking mechanics affected?

• Should I be worried?

In this blog, we’ll look at how common leg length differences are, how they’re measured, and whether they actually increase your risk of injury.

How Common Is Leg Length Inequality?

Leg length differences are extremely common.

A 2005 review by Knutson found that around 90% of the population has some degree of leg length inequality, with the average difference being approximately 5.2 mm.

So if one leg is slightly shorter than the other, you are very much in the majority.

The key question is not whether a difference exists, but whether it is large enough to be clinically relevant.

How Is Leg Length Measured?

There are several ways clinicians may assess leg length, including tape measurements, visual assessments, pelvic landmarks, or clinical screening tests.

However, these methods can be prone to error.

The most accurate way to measure true leg length difference is with imaging, such as a standing radiograph of the full lower limb. This allows a more precise measurement of the bony length of each leg.

That said, imaging is not always required. In many cases, the more important question is whether the leg length difference appears to be contributing to the person’s symptoms, movement pattern, or load tolerance.

How Much Difference Is Considered Relevant?

Small differences are common and usually not a concern.

Knutson’s 2005 review concluded that leg length inequalities under approximately 15–20 mm are unlikely to be clinically significant for most people.

The same review found that only around 6.4% of the population has a difference greater than 14 mm, meaning larger discrepancies are relatively uncommon.

There are some childhood conditions that can lead to more significant leg length differences, but these are rare.

What About Leg Length and Injury?

This is where things get interesting.

Despite how often leg length inequality is blamed for pain or injury, the research does not strongly support it as a major injury risk factor in most people.

A 2018 study of high school cross-country runners found that leg length inequality was not associated with overall injury risk. The one exception was that males with a leg length difference greater than 1.5 cm had a higher likelihood of lower leg injuries, such as shin or calf injuries.

A 2006 study of military recruits also found no significant difference in injury rates between those with leg length inequality and those without.

When it comes to low back pain, leg length differences can influence pelvic position or spinal curvature, but it remains unclear whether this directly causes pain. The current evidence is limited and does not support blaming small leg length differences as a major driver of low back pain.

The Multifactorial Nature of Injury

Most injuries are not caused by one single factor.

Training load, strength, recovery, sleep, footwear, tissue capacity, previous injury history, biomechanics, and lifestyle stress can all play a role.

So while a larger leg length difference could contribute to symptoms in some cases, it is rarely the whole story.

This is why it’s important not to look at leg length in isolation. The more useful question is:

Does this difference appear to be relevant for this person, with this injury, at this point in time?

Should You Use a Heel Lift?

Not everyone with a leg length difference needs a heel lift.

For small differences, especially if there are no symptoms, a heel lift is often unnecessary.

A heel lift may be considered if:

• The difference is larger

• Symptoms consistently appear on one side

• There is a clear link between the discrepancy and the person’s pain or function

• Other contributing factors have also been addressed

Even then, changes should usually be introduced gradually and monitored carefully.

Key Takeaways

Most people have slightly different leg lengths.

Small differences are common and usually not clinically meaningful.

Significant leg length differences are relatively rare.

The current evidence does not support leg length inequality as a major injury risk factor for most people.

Larger discrepancies may matter in some cases, but they need to be considered alongside the full clinical picture.

So, does having one leg longer make you more likely to get injured?

For most people, probably not.

But in some cases, especially when the difference is larger, it may be one piece of the puzzle.

References

• Goss DL, Moore JH, Slivka EM, Hatler BS. Comparison of injury rates between cadets with limb length inequalities and matched control subjects over 1 year of military training and athletic participation. Mil Med. 2006;171(6):522-525.

• Knutson GA. Anatomic and functional leg-length inequality: a review and recommendation for clinical decision-making. Part I, anatomic leg-length inequality: prevalence, magnitude, effects and clinical significance. Chiropr Osteopat. 2005 Jul 20;13:11.

• Rauh, M. J. (2018). "LEG-LENGTH INEQUALITY AND RUNNING-RELATED INJURY AMONG HIGH SCHOOL RUNNERS." Int J Sports Phys Ther 13(4): 643-651.