Hello！
My name is Ikuko Murata, I'm a physical therapist and a personal trainer (Tokyo).
From this article, I will explain about "leg length discrepancy" in a series. (Series table of contents）
The first is about "How does the leg length discrepancy affect the knee".
【table of contents】
５. Summary
１. Dose the leg length discrepancy cause knee pain?
Yes.
If your leg length has a difference in right and left, I think your knees tend to hurt.
Especially, it's seems that the knees suffer a direct effect from the leg length discrepancy, doesn't it?
It's easy to imagine that it is not good for the knees.
So, which knee will hurt?
The shorter side?
The 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 in the shorter leg" .
2. What kind of stress in the shorter leg?
In the shorter side knee, there is an "impact" stress.
If you walk with a leg length discrepancy, 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 discrepancy: walking video available)
In a 2010 American study, it was reported that "a leg length discrepancy of 0.5cm or more increases the risk of knee osteoarthritis in the shorter leg."
References : Harvey WF, Yang M, Cooke TD, et al.（2010）ASSOCIATIONS OF LEG LENGTH INEQUALITY WITH PREVALENT, INCIDENT, AND PROGRESSIVE KNEE OSTEOARTHRITIS: A COHORT STUDY. Ann Intern Med. 2010 Mar 2.
The amazing point of this paper is the huge amount of data of 2964 people.
In addition, the leg length discrepancy is measured by an "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 discrepancy 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, does it mean that longer side knee is okay?
No no no... it's not okay.
On the longer side knee, there is often a "distortion stress" .
"Distortion stress" does not directly lead to pain as quickly as "impact stress", but it gradually and steadily damages joints.
For example, the right leg is shorter than the 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 or put in or put out the longer side of the knee, the functional length of the leg can be shortened even if the actual bone length does not change.
In other words, the longer leg can be shortened by distorting the knee.
(The adaptability of human beings is amazing!)
And this distortion of the bending or putting in or putting out the knee 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 hurt and the longer side knee sometimes hurt too.
Such clients often have the knee joint broken in the longer side, even if the pain is not so serious compared to the 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.)
In the paper I've introduced above, there was one more point I would like for you to pay attention to.
That is, the risk of knee deformation increases with a leg length discrepancy of "0.5 cm or more".
The paper suggests that even a leg length discrepancy of only 5 mm can affect the knee.
As I will write on my other blog later, it is traditionally said that "a leg length discrepancy of 3 cm or less is within the acceptable range" among the Japanese physical therapists' world.
3 cm.
It's not 3 mm.
Insole approach to millimeter unit is actually not common in physical therapy in Japan.
So honestly I'm different from other physical therapists in the hospital, but this research supports me!
To summarize this research with my personal opinion,
It is said that "a leg length discrepancy 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 the leg length discrepancy! Especially the shorter side!
I think that if we do not overlook this simple problem of a leg length discrepancy and deal with it, we can prevent a considerable proportion of knee pain and deformity.
I really hope that the leg length discrepancy check up 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 discrepancy of only 5 mm affects the knee.
・ We should be able to prevent a lot of knee pain by checking the leg length discrepancy!
The same content is explained on YouTube → YouTube
Thank you for reading.
I hope this article will be a helpful to improve your body!
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