How does the leg length discrepancy affect the knee?


My name is Ikuko Murata, I'm a physical therapist and personal trainer (Tokyo).

From this article, I will explain about "leg length difference" in a series. (Series table of contents

The first is about "How does the leg length difference affect the knee".

【table of contents】

1、Dose the leg length cause a knee pain?

2、What kind of stress in the shorter leg?

3、What kind of stress in the longer one?

4、How much difference become a stress?


1. Dose the leg length cause a knee pain?


If your leg length have a difference in right and left, I think your knees tend to hurt.

Especially, it's seems that "knee" suffer a direct effect from it, isn't it?

It's easy to image that it is not good for the knees.

So, which knee will hurt?

Shorter side?

Longer side?

Which do you think?

The answer is "both", but in my clinical practice, I feel that the shorter knee often hurts.

So, first of all, I will explain from the topic "what kind of stress is applied to the knees for shorter leg" .

2. What kind of stress in the shorter leg?

In the shorter side knee, there is a "impact" stress.

If you walk with a leg length difference, the "impact" will be stronger on the shorter leg landing.

The reason is simple: the center of gravity drops at the moment of landing. Because ... it's short.

On the shorter landing, the center of gravity drops with the "impact", and on the longer landing the center of gravity rises.

It means that the walking rhythm becomes non-constant.

(Case study article on leg length difference: walking video available)

In a 2010 American paper, there was a study that reported that "a leg length difference of 0.5 cm or more increases the risk of knee osteoarthritis in the shorter leg."

* I'm sorry if the interpretation of the treatise is wrong. If you are interested, please go directly ↓


The amazing point of this paper is the huge amount of data of 2964 people.

In addition, the difference in leg length is measured by "X-ray of the entire leg!". Not only the pelvis part, but also the X-ray to the end of the tibia.

Furthermore, this study follows the course of two and a half years.

Now we have found this study is reliable, let me repeat the results.

"A leg length difference of 0.5 cm or more increases the risk of knee osteoarthritis in the shorter leg."

After all, the knees of the short legs hurt first. .. .. I read while looking back on my clinical practice.

3. What kind of stress in the longer leg?

So, dose it mean longer side knee OK?

No no no... it's not OK.

On the longer side knee, often there is a "distortion stress" .

"Distortion stress" does not directly lead to pain as quickly as "impact stress", but it gradually but steadily damages joints.

For example, the right leg is shorter than left.

You can't extend your shorter right leg, but how about your longer left leg?

Can you make it short?

Yes, you can.

If you bend the left knee or make the O-leg or X-leg,

Even if the actual bone length does not change, the functional length of the leg in actual use can be shortened.

In other words,

The longer leg can make short by distorting the knee.

(The adaptability of human beings is amazing!)

And this distortion of bending knee or O-leg or X-leg will steadily put a burden on the knee joint even little by little.

In clinical practice, I sometimes encounter clients who say that the shorter side knee always hurts, but the longer side knee sometimes hurts.

Such kind of client often have the knee joint broken in longer side, even if the pain is not so serious compared to shorter side.

In addition, the pain in the shorter knee can be relieved unexpectedly by the insole, but the pain in the longer knee is the result of distortion and does not improve so quickly.

(Additionally, if the destruction of this joint is excessive, surgery is suggested.)

4. How much difference become a stress?

In the above paper I introduced, there was one more point I would like you to pay attention to.

That is, the risk of knee deformation increases with a leg length difference of "0.5 cm or more".

The paper suggests that even a leg length difference of only 5 mm can affect the knee.

As I will write on other blog later, it is traditionally said that "a leg length difference of 3 cm or less is within the acceptable range" among Japanese physical therapists world.


It's not 3mm.

Insole approach to millimeter unit is actually not common in physiotherapy.

So honestly I'm little strange physical therapist in the hospital, but this research supports me!

To summarize this research with my personal opinion,

It is said that "a leg length difference of 3 cm or less is an acceptable range" in the world of physical therapists, but this study showed that there is a risk of knee osteoarthritis even if it is only 5 mm! There are many knee pains that can be prevented if we focus on this point! Especially the shorter one!

I think that if we do not overlook this simple problem of leg length difference and deal with it, we can prevent a considerable proportion of knee pain and deformity.

I really hope that the leg length difference check will be normal.

5. Summary

・ The knee of the shorter leg hurts due to "impact" stress.

・ The knee of the longer leg breaks due to "distortion" stress.

・ There is a study that even a difference of only 5 mm affects the knee.

・ We should be able to prevent a lot of knee pain by checking the leg length difference!

The same content is explained on YouTube → YouTube

Thank you for reading.

I hope this article will be a helpful information to improve your body!

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