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Many orthopedic specialists recommend using foot insoles, for addressing various issues - including small discrepancies between the lengths of one's legs.

Now, such a discrepancy is a tricky measure. Obviously, one can't measure it using the feet. If one stands or lies down - the softer tissue is compressed differently between asymmetric legs. Plus, the bones themselves might not (I would think) be positioned at the exact same angles.

My question is: How should (and how do) relevant specialists measure the length discrepancy, or perhaps I should say the discrepancy to be accounted for/corrected with an insole?

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    Have you seen this? medicalsciences.stackexchange.com/questions/13560/…
    – Carey Gregory
    Nov 6, 2023 at 14:58
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    "Obviously, one can't measure it using the feet. If one stands or lies down - the softer tissue is compressed differently between asymmetric legs. Plus, the bones themselves might not (I would think) be positioned at the exact same angles." I'm not sure any of that matters. Did you google "how to measure leg length discrepancy"? I was taught to do so in a very straightforwardly manner. Nov 6, 2023 at 17:32
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    1) The way to go with anatomical or functional length differences would be thickening of the outer sole, not inlays. 2) There are a lot of sources out there on how it is done. It involves palpable bone structures and you measure the upper and lower leg separately so that one does not have to deal with joint positions. Nov 6, 2023 at 18:53
  • @CareyGregory: That question is interesting! I've been wondering about that myself. But the answer is an infinite list of syndromes/conditions, so not very useful if you're a patient rather than a therapist :-(
    – einpoklum
    Nov 6, 2023 at 20:24
  • @PhilipKlöcking: 1. Perhaps I misspoke. I meant to say "some kind of object you insert into your shoe", nothing more specific than that. 2. Can you make this comment into an answer?
    – einpoklum
    Nov 6, 2023 at 20:31

1 Answer 1

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First off, there are two kinds of leg length difference (LLD): anatomical and functional. All citations following are from Physiopedia. If you are interested in the matter, I suggest you just read the whole article.

Anatomical LLD

Definition and measurement

Structural limb length inequality. It’s a physical (osseous) shortening of one lower limb between the trochanter femoral major and the ankle mortise.

Thus, it can simply be measured using very characteristic bone structures. Either by radiographics or by using a simple tape measure: you can palpate the trochanter major, the lateral joint space of the knee joints, and obviously the lateral ankle. Thus, one palpates them, takes the measures from trochanter major to knee joint space and from there to the lateral ankle, and adds them. Plus point here is that it makes no difference whether people are physically able to extend hip and knee joints to a neutral position.

Development

Congenital conditions include mild developmental abnormalities found at birth or childhood, whereas acquired conditions include trauma, fractures, orthopedic degenerative diseases, and surgical disorders such as joint replacement:

  • Idiopathic developmental abnormalities
  • Fracture
  • Trauma to the epiphyseal endplate prior to skeletal maturity
  • Degenerative disorders
  • Legg-Calvé-Perthes Disease
  • Cancer or neoplastic changes
  • Infections

From my experience, the most common reasons for pathological LLD are the trauma (esp. fracture into) to the epiphyseal endplate (which can stop or alter bone growth), and badly done joint replacements.

Prevalence

A systemic review evaluating the prevalence of LLD by radiographic measurements revealed that 90% of the normal population had some type of variance in bony leg length, with 20% exhibiting a difference of >9 mm.

This shows that obviously, it is not a bad thing as such. Problems occur mostly beyond 1.5 cm from what we learned in our physio education.

Functional LLD

Definition and measurement

Non-structural shortening. It is a unilateral asymmetry of the lower extremity without any shortening of the osseous components of the lower limb. FLLD may be caused by an alteration of lower limb mechanics, such as joint contracture, static or dynamic mechanical axis malalignment, muscle weakness, or shortening. It is impossible to detect these faulty mechanics using a non-functional evaluation, such as radiography.

Thus, you basically need to see these persons walk and be able to make out and interpret certain signs. There is no "measuring" those in the classic sense.

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  • So, a measurement of anatomical LLD which yields a value very close to 0 would suggest a functional LLD as an explanation of observed behavior?
    – einpoklum
    Nov 6, 2023 at 21:16
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    @einpoklum Most definitely. One would look at joint positions during standing and walking and see whether one side of the hip is lower due to one leg being more straight in function, basically. As the legs are anatomically not that different, a non-functional pelvis position and movement has to show in joint positions. Nov 6, 2023 at 21:21
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    +1, Nice answer. "All things being equal..." is a rare thing, even between two sides of the same body. :) Nov 10, 2023 at 13:22

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